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Abstract
Self-powered ultraviolet photodetectors generally operate by utilizing the built-in electric field within heterojunctions or Schottky junctions. However, the effectiveness of self-powered detection is severely limited by the weak built-in electric field. Hence, advances in modulating the built-in electric field within heterojunctions are crucial for performance breakthroughs. Here, we suggest a method to enhance the built-in electric field by taking advantage of the dual-coupling effect between heterojunction and the self-polarization field of ferroelectrics. Under zero bias, the fabricated AgNWs/TiO2/PZT/GaN device achieves a responsivity of 184.31 mA/W and a specific detectivity of 1.7 × 1013 Jones, with an on/off ratio of 8.2 × 106 and rise/decay times reaching 0.16 ms/0.98 ms, respectively. The outstanding properties are primarily attributed to the substantial self-polarization of PZT induced by the p-GaN and the subsequent enhancement of the built-in electric field of the TiO2/PZT heterojunction. Under UV illumination, the dual coupling of the enhanced heterojunction and the self-polarizing field synergistically boost the photo-generated carrier separation and transport, leading to breakthroughs in ferroelectric-based self-powered photodetectors.
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1. Introduction
Self-powered ultraviolet (UV) photodetectors (PDs) allow for efficient UV light detection without the requiring external power sources. This feature presents extensive application potential across domains including medical analysis [1], wireless environmental monitoring, and defense technology [2]. The conventional self-powered UV photodetectors primarily depend on the built-in electric field within heterojunctions or Schottky junctions for the segregation and transport of photogenerated carriers, leading to the generation of detection current [3]. However, the limited built-in electric field of heterojunctions or Schottky junctions curtails the effectiveness of self-powered UV PDs in the absence of bias voltage, thus hindering their practical application and advancement [4]. To enhance the built-in electric field and ameliorate the performance of self-powered UV PDs, researchers have have suggested a variety of tactics. These encompass enhancing the crystal quality of heterojunctions or Schottky junctions, along with integrating the photovoltaic effect with the piezoelectric, pyroelectric, and ferroelectric polarization effects, and other approaches, to amplify the impetus for the segregation of photogenerated carriers [3]. However, the improvement of crystal quality in heterojunctions frequently demands intricate fabrication processes and incurs elevated production expenses. The piezoelectric effect hinges on external pressure for activation, while the pyroelectric effect commonly presents the drawback of a large dark current. Consequently, there remains a necessity for more efficacious approaches and strategies to enhance the built-in electric field and boost the efficiency of self-powered UV PDs. In recent years, the self-polarization field (Esp) and depolarization field (Edp) of ferroelectric materials have demonstrated significant potential in augmenting the built-in electric field and propelling the development of self-powered UV PDs [5,6]. Nevertheless, the Edp of ferroelectric material still requires electric power to apply the electric field, which undermines the goal of energy conservation and power reduction. To construct a self-enhanced self-powered UV PD, the ferroelectric material with strong Esp emerges as a propitious contender, obviating the need for external power support.
The Esp signifies the macroscopic polarized electric field that ferroelectric materials exhibit naturally. This phenomenon occurs as these materials spontaneously generate internal electric domains with specific orientations, even in the absence of an external electric field [7]. Previous reports have indicated that the self-polarization effect can effectively modulate the built-in electric field of heterojunction to enhance the optoelectronic detection performance. For example, Fang et al. fabricated a self-polarization-enhanced BaTiO3 (BTO)-ZnO UV PD, which achieved a rise/decay time of 0.11 ms/5.80 ms and an on/off ratio of 1.43 × 104 under a bias voltage of 3 V [8]. Wei et al. fabricated heterojunctions composed of BiEuFeO (BEFO) and Nb-doped SrTiO3, and these PDs exhibited a responsivity of 0.64 mA/W under zero bias voltage [9]. Li et al. synthesized self-polarized BixFeO3 films (x = 1, 1.3, 1.5, 1.7) using the sol-gel method, and the resulting Au/BixFeO3/LNO devices demonstrated a detectivity of 1.35 × 1011 Jones with a rise/decay time of 5 ms/6 ms [10]. Su et al. demonstrated that the mesoporous TiO2 PD prepared on self-polarized BTO increased the on/off ratio by 17-fold in comparison to pure mesoporous TiO2 [11]. Despite certain improvements achieved by utilizing the self-polarization effect or the coupling of this effect with heterojunctions, the performance of these devices has not yielded extraordinary outcomes due to the constraint of low Esp strength. Therefore, the development of ferroelectric materials with strong Esp, as well as efficient coupling effects in heterojunctions, is crucial for enhancing the self-powered optoelectronic detectors.
Lead zirconium titanate (Pb(ZrnTi1-n)O3, PZT) represents high-performance ferroelectric semiconductor material [12,13], and its self-polarization effect and photovoltaic effect have been extensively studied [14–18]. Nevertheless, PZT thin films produced through conventional methodologies still manifest relatively modest Esp. Sun et al. revealed that the polarity of PZT can be manipulated via a GaN substrate, leading to enhanced crystallinity [19], diminished lattice mismatch [20], and a more pronounced negative electrocaloric effect [21]. Additionally, PZT deposited on a GaN substrate showcased a markedly favored (111)-orientation in the study conducted by Dey et al [22]. Moreover, Peng et al. observed that the GaN substrate induced a phase transition within PZT, from a tetragonal phase to a rhombohedral phase, thereby intensifying the self-polarization effect [21]. In this study, we fabricated (111)-oriented PZT (PbZr0.3Ti0.7O3) thin films on a p-GaN substrate, producing a substantial Esp. Subsequently, high-quality TiO2 was deposited onto PZT to construct a self-powered UV PD, where the dual-coupling effect enables distinguished optical detection properties. The robust Esp of PZT enhances the built-in electric field at the heterojunction between TiO2 and PZT, thereby notably amplifying the impetus for segregating photo-generated electron-hole pairs, leading to a substantial advancement in the photodetection capabilities of the device. Under zero bias voltage, the self-powered UV PD that we fabricated, utilizing the AgNWs/TiO2/PZT/GaN structure, showcases a notable responsivity (R) of 184.31 mA/W at a low optical power density of 0.013 mW/cm2 and its rise and decay times reach to 0.16 ms and 0.98 ms, correspondingly. The external quantum efficiency (EQE) reaches an astonishing 62%, and the specific detectivity (D*) attains a magnitude of 1.7 × 1013 Jones. The on/off ratio reaches 8.2 × 106, and the device upholds outstanding stability over extended periods of operation. Through capitalizing on the dual coupling between the self-polarization field of PZT and the built-in electric field of TiO2/PZT heterojunction, we significantly enhance the optical detecting performance of the device, offering a low-cost and practical approach for developing high-performance and self-enhanced self-powered UV photodetectors.
2. Results and discussion
2.1 Device structure and principle
Figure 1(a) illustrates the three-dimensional schematic of the self-polarization double-coupling self-powered ultraviolet (UV) photodetector (PD). The device is mainly composed of AgNWs/TiO2/PZT/GaN, where TiO2 serves as the main optical-absorbing layer. Transparent AgNWs thin film and small-area silver electrodes are deposited onto the surfaces of TiO2 and PZT, respectively, for the purpose of capturing photogenerated carriers. The device's operational principle, depicted in Fig. 1(b), at the PZT/GaN interface holes within p-GaN traverse to the PZT side and induce the negative charges of PZT, modulating a reorientation of the ferroelectric domains within PZT, resulting in a pronounced self-polarization field (Esp). In comparison to the natural state, the reorientation of ferroelectric domains in PZT increases the concentration of positive charges in the upper side of PZT, thereby attracting more electrons from titanium dioxide towards PZT motion. This leads to the formation of an enhanced built-in electric field at the TiO2/PZT interface. Ultimately, the strong Esp induced by p-GaN and the enhanced TiO2/PZT heterojunction generate a synergistic coupling effect, boosting the separation and transport of photogenerated carriers and achieving superb self-powered UV photodetection performance. Upon exposure to ultraviolet light at a wavelength of 365 nm and an optical power density of 59.29 mW/cm2, the device attains a detection current of 49 µA under zero bias voltage, as illustrated in Fig. 1(c). The device's current under dark conditions measures approximately 6 pA [Fig. 1(d)]. Deriving from these values, the device presents a peak on/off ratio of up to 8.2 × 106. The inset in Fig. 1(e) depicts the optical responsivity (R) and external quantum efficiency (EQE) of the device under different wavelengths. The device accomplishes a R of 184.31 mA/W and an EQE of 0.62 at 365 nm, and demonstrates a remarkable UV (365 nm) /visible (400 nm) rejection ratio of 274. In comparison to self-powered UV PDs with ferroelectric materials, our AgNWs/TiO2/PZT/GaN device made a breakthrough [Fig. 1(e)].
Fig. 1. Structure, working principle, and fundamental performance of AgNWs/TiO2/PZT/GaN Device. The three-dimensional model (a) and the working principle (b) of the device. The Ip (c) and Id (d) of the device under 365 nm light illumination at zero bias. The performances of AgNWs/TiO2/PZT/GaN detector compared with those of devices containing ferroelectric materials (e).
2.2 Materials characterization
To gain deeper insights into the superior performance and underlying physical mechanisms of the AgNWs/TiO2/PZT/GaN device, a comprehensive characterization was undertaken. Figure 2(a) presents a cross-sectional scanning electron microscope (SEM) image of the device, showing distinct layers of thin films. The GaN film measures approximately 1 µm in thickness, PZT measures around 1.1 µm, and TiO2 possesses a thickness of about 350 nm. Figure 2(b) displays the surface SEM of AgNWs, along with a magnified view. The AgNWs are firmly affixed to the TiO2 surface, featuring an estimated diameter of 60 nm. Figure 2(c) exhibits the surface SEM of the TiO2 film, signifying a densely grown film. Figure 2(d) presents the surface morphology of the PZT film, characterized by its uniform and smooth appearance. Elemental composition analysis was conducted on the PZT film, and Supplement 1, Fig. S1, depicts the outcomes of the energy dispersive spectrometer (EDS) test, revealing a homogenous distribution of elements with a Pb/Zr/Ti ratio of roughly 1:0.3:0.7. To ascertain the crystalline attributes of the thin films, X-ray diffraction (XRD) measurements were executed on samples both with and without TiO2, as evidenced in the lower section of Fig. 2(e). Prominent characteristic peaks at 2θ= 25.324°, 36.988°, 37.86°, and 38.6°denote TiO2 crystals, aligning with the anatase phase (JCPDS card number 84-1286). To mitigate potential PZT signal interference, a grazing incidence X-ray diffraction (GIXRD) measurement was conducted on TiO2 at an angle of 1.
Fig. 2. Material characterization. Scanning electron microscope(SEM) images of the cross-section (a), AgNWs surface (b), TiO2 surface (c) and PZT surface (d) of the AgNWs/TiO2/PZT/GaN device. XRD pattern of the sample with and without TiO2 film(e). Voltage-Dependent Hysteresis Loop Diagram of PZT Film Ranging from 5 V to 45 V (f).
The results are shown in Fig. S2, which are consistent with the results shown in Fig. 2(e). The XRD spectrum of the PZT/GaN/sapphire sample [upper half of Fig. 2(e)] shows that PZT exhibits a perovskite structure, with the (111) plane displaying strong diffraction peaks, indicating its dominant crystal orientation. In accordance with previous literature [21], p-GaN possesses the capacity to modulate the crystal orientation of PZT, resulting in a robust polarization effect within PZT under the dominant orientation of the PZT (111) plane. The voltage-dependent hysteresis loop of PZT spanning from 5 V to 45 V [Fig. 2(f)] corroborates its substantial Esp, which underpins the distinguished performance of the device. Notably, the loop diagram manifests pronounced asymmetry and leakage current [lower right corner of Fig. 2(f)]. As reported in ferroelectric/GaN systems [23,24], it possesses a strong depolarization effect and certain conductivity that favor to enhance the optical detection performance.
The transmittance spectra of different thin films are depicted in Supplement 1, Fig. S3(a). The AgNWs film displays a transmittance exceeding 80% for light spanning from 300 nm to 800 nm, along with an 88.7% transmittance for UV light at a wavelength of 365 nm. Subsequent to spin-coating AgNWs electrodes onto the TiO2 film, the transmittance spectrum of the sample shifts downward, leading to a general reduction in optical transmittance. However, this alteration does not impact the absorption edge of TiO2. The transmittance spectra are transformed into (αhν)2 versus hν plots using Tauc's method [25], as depicted in Fig. S3(b). The absorption coefficient α of PZT is extracted from ellipsometry analysis (Fig S4). The bandgaps of TiO2 and PZT are determined as 3.4 eV and 3.75 eV, respectively. For the purpose of obtaining the band structure of the device, VB-XPS measurements are carried out on each thin film [Fig. S3(c)]. The energy difference between the valence band and the Fermi level is discerned from the cut-off edge of the spectrum, resulting in values of 2.3 eV and 1 eV for TiO2 and PZT, respectively. The energy level alignment of each layer in the device is depicted in Fig. S3(d), with the work functions of AgNWs, TiO2, and PZT reported in the literatures as 4.3 eV [26,27], 4.5 eV [28], and 5.5 eV [29,30], respectively. Finally, the band diagram of the device is illustrated in Fig. S5. A heterojunction is formed at the TiO2/PZT interface, and under the influence of the Esp, the PZT band inclines upward. This band structure of PZT enhances the transport of photo-generated carriers, facilitating the remarkable performance of the device. Moreover, an ohmic contact is established between the upper electrode AgNWs and TiO2, while no substantial barrier formation is observed between the lower electrode Ag and PZT (as evident in Fig. S6), guaranteeing the effortless conduction of charge carriers within the device.
To scrutinize the robust self-polarization effect induced in PZT thin films by p-GaN, we performed piezoresponse force microscopy (PFM) testing and analysis. The conclusive findings are depicted in Fig. 3. The 2D AFM image showcased in Fig. 3(a) unveils a relatively uniform and smooth microstructure, complemented by the corresponding 3D depiction in Fig. 3(b). Figure 3(c) offers insights into the height distribution of the film, quantifying a root mean square roughness (RMS) of 960 pm for PZT. The out-of-plane ferroelectric domain distribution illustrated in Fig. 3(d) demonstrates the concentration of ferroelectric domains in the negative phase, signifying a well-established single-domain structure of PZT in the out-of-plane orientation. This assertion gains further substantiation through the out-of-plane ferroelectric domain phase distribution depicted in Fig. 3(e), where the phase is solitary and centers around -110°. This indicates a potent self-polarization effect in the PZT film induced by p-GaN substrate, with the polarization direction centered at -110°. The in-plane ferroelectric domain distribution of PZT is depicted in Fig. 3(f), revealing the absence of a solitary domain orientation within the plane. The phase distribution in Fig. 3(g) discloses that the in-plane ferroelectric domain phase is concentrated between -100° and 90°. Figure 3(h) further elucidates the self-polarization dual-coupling mechanism of the AgNWs/TiO2/PZT/GaN device. The transition of holes in p-GaN results in a positively charged depletion layer at the PZT interface, inducing the deflection of the internal dipoles in PZT and leading to a substantial downward self-polarized electric field in PZT [as confirmed in Fig. 3(e) and Fig. 2(f)]. Subsequently, the Esp induces a significant electron transition from the TiO2 interface to the PZT interface, generating an enhanced built-in electric field (ETiO2/PZT) of the heterojunction TiO2/PZT [Fig. 3(h)]. Finally, the dual-coupling of enhanced ETiO2/PZT and Esp enables the device's pronounced capability for the separation and transport of photo-generated carriers.
Fig. 3. Characterization of strong self-polarization effect in PZT/GaN samples. AFM 2D (a) and 3D (b) images, along with corresponding surface height distribution plot (c) of PZT thin film. Out-of-plane domain distribution (d) and phase image (e) of the PZT thin film. In-plane domain distribution (f) and phase image (g) of the PZT thin film. Explanation of self-enhancement principle (h).
2.3 Output properties
Figure 4 and Fig. 5 illustrate the output characteristics of the AgNWs/TiO2/PZT/GaN self-powered UV PD. In Fig. 4(a), the I-T curve of the AgNWs/TiO2/PZT/GaN self-powered UV PD under 365 nm light illumination is shown for optical intensities ranging from 0.013 mW/cm2 to 59.29 mW/cm2. As the optical intensity increases, the steady-state photocurrent of the device is raised from 40 nA to 49 µA. The V-T curves are depicted in Fig. 4(b). The open-circuit voltage rises from 0.21 V to 1.02 V with variations in optical intensity. The distribution map of output current [Supplement 1, Fig. S7(a)] and output voltage [Fig. S7(b)] with various optical power densities indicate that the AgNWs/TiO2/PZT/GaN self-powered UV PD possesses favorable photodetection performance even at diminished light intensities and demonstrates a discerning detection sensitivity to fluctuations in optical power density.
Fig. 4. I-T curves (a) and V-T curves (b) of self-powered UV PD utilizing AgNWs/TiO2/PZT/GaN under varied optical power densities at 365 nm illumination.
Fig. 5. I-V curves (a) of AgNWs/TiO2/PZT/GaN PD under 365 nm illumination and dark conditions, along with the rise time (b), decay time (c), and stable output graph after long-term operation of 10010 seconds (d). The relationships between the responsivity, detectivity, and photocurrent at different optical power densities (e).
The semi-log scale I-V curves of the AgNWs/TiO2/PZT/GaN PD under light and dark conditions are shown in Fig. 5(a) (the inset represents the I-V curve under rectangular coordinate system), exhibiting a rectifier characterization with a rectification ratio of ∼2485 at ±2 V. The significant contrast between light and dark conditions suggests a pronounced photovoltaic (PV) effect in the device. This characteristic is primarily attributed to the Esp of PZT, which modulates the built-in electric field at the TiO2/PZT heterojunction interface. Figure 5(b) and Fig. 5(c) present the response time of the AgNWs/TiO2/PZT/GaN self-powered UV PD. The response time is defined as the duration needed for the photocurrent to ascend from 10% to 90% (rise time) and descend from 90% to 10% (decay time). The rise time is 0.16 ms, and the decay time is 0.98 ms. The fast response time indicates that the self-polarization double-coupling effect in our device accelerates the separation and transportation of photo-generated carriers. Figure 5(d) displays the current response pattern of the device under continuous illumination, utilizing an optical power density of 59.29 mW/cm2 at a wavelength of 365 nm for a duration of 10,010 seconds, with illumination periods of 3 seconds each. The device demonstrates stable photoresponse over extended periods of operation. Additionally, the responsivity (R) and the specific detectivity (D*) are vital metrics for assessing the performance of a photodetector. These metrics can be calculated using the following formulas [1,31,32]:
where Ip represents the photocurrent, Id stands for dark current, P denotes the incident optical power density, and S represents the effective light-illuminated area of the device (0.016 cm2). Figure 5(e) displays the values of R and D* for the device at varying UV light powers with a wavelength of 365 nm. As the optical power density increases, both R and D* decrease. At an optical power density of 59.29 mW/cm2, the responsivity is 47.95 mA/W, and the detectivity is 4.50 × 1012 Jones. This feature indicates that our device also has commendable detection performance under strong UV light. The correlation between photocurrent Ip and P can be fitted through empirical formulas [33–35]: where C stands for a constant and a represents the empirical fitting constant. The fitting outcomes indicate a weak linear correlation between the Ip and P, aligning with the fluctuations in R and D*. The alterations in R and D* in response to light intensity can be primarily attributed to the following factors: at lower optical power densities, effective separation of the majority of photo-generated carriers occurs due to the double-coupling effect between Esp and ETiO2/PZT, resulting in remarkable R and D*. However, at higher optical power densities, self-heating effects increase the recombination and scattering of photogenerated charge carriers, resulting in a decline in both D* and R [6,36]. Our AgNWs/TiO2/PZT/GaN PD showcases outstanding performance in contrast to other self-powered devices, as illustrated in Table 1. Whether in terms of R, D*, or rise/decay time, our device demonstrates remarkable performance, underscoring the notable benefit of the dual-coupling effect.2.4 Comparative analysis
In order to visually illustrate the significant breakthrough achieved by the designed AgNWs/TiO2/PZT/GaN PD, we fabricated AgNWs/PZT/GaN PDs for comparison. Under UV illumination with the wavelength of 365 nm and the optical power density of 0.013 mW/cm2, the R of AgNWs/TiO2/PZT/GaN PD is 18 times higher than that of AgNWs/PZT/GaN PD at zero bias. The dark current (Id) of the AgNWs/PZT/GaN device is approximately 65 pA, as shown in Supplement 1, Fig. S8, which is a 10-fold increase compared to the 6 pA of the dual-coupling device. When the optical power density is 59.29 mW/cm2, the photovoltage and photocurrent of dual-coupling device are about 10 times higher than those of AgNWs/PZT/GaN PD. In turn, polarization treatments were conducted on the AgNWs/PZT/GaN devices to investigate the enhancement effect of the depolarization field (Edp) of PZT. The electric field was considered as in the “poling down” state when directed from GaN to PZT, and conversely as a “poling up” state in the opposite direction, and the applied voltage is 40 V. The duration of polarization for all treatments is 10 seconds. The photocurrent and open-circuit voltage of the AgNWs/PZT/GaN were contrasted with those of the AgNWs/TiO2/PZT/GaN after different polarization treatments, under the same light illumination, as presented in Fig. S9(a) and Fig. S9(b), respectively. The R of the AgNWs/PZT/GaN device is depicted in Fig. S10, while the rise and decay times are indicated as 0.38 ms and 0.82 ms, respectively, in Fig. S11. Elaborate comparative data is tabulated in Table S1. Obviously, the appropriate polarization treatment can effectively improve the performance of AgNWs/PZT/GaN devices. However, the performance of AgNWs/TiO2/PZT/GaN PD is significantly better than that of all AgNWs/PZT/GaN devices, indicating the effectiveness and superiority of the dual-coupling effect. On the one hand, the p-GaN substrate induces a strong Esp within the PZT layer and this Esp coupling enhances the built-in electric field at the interface of the TiO2/PZT heterojunction. On the other hand, the coupling effect of the two electric fields Esp and ETiO2/PZT foster the efficient separation and transport of photogenerated electron-hole pairs and thus substantial performance improvements are achieved.
Table 1. Comparison of self-powered UV PDs
3. Experimental section
3.1 Device fabrication
The PZT thin film was synthesized through the sol-gel method. Initially, lead acetate trihydrate (Pb(CH3COOH)·3H2O) was introduced into a mixture of glacial acetic acid and ethanol and mixed at room temperature. Simultaneously, zirconium n-propoxide (Zr(OC3H7)4) and titanium butoxide (Ti(OC4H9)4) were individually introduced into a blend of glacial acetic acid and acetone. These solutions were mixed at 80 °C for 2 hours to yield the PZT precursor solution and then cooled to room temperature for storage. Following that, the formulated PZT precursor solution was spin-coated onto a p-GaN substrate that had undergone cleaning with acetone, isopropanol, ethanol, and deionized water. Each coating was applied through spin-coating at 3000 rpm for 30 seconds, subsequently dried at 350 °C for 1 minutes, pyrolyzed on a hotplate at 550 °C for 2 minutes, and finally crystallized at 750 °C for 1 minute in air. This procedure was repeated 10 times to get a realized thickness.
A thin TiO2 layer was deposited onto the PZT film utilizing the magnetron sputtering technique. Sputtering was carried out via radio frequency (RF) at an approximate distance of 9 cm between the target (99.99% pure TiO2) and the sample. Before commencing the experiment, the vacuum chamber was evacuated to a pressure of 3.0E-4 Pa, and the substrate was preheated to 200 °C. Subsequently, argon gas was introduced into the chamber at a flow rate of 80 sccm, serving as the sputtering gas, while the chamber pressure was adjusted to 0.77 Pa. An RF power of 150 W was employed. Following the deposition of the TiO2 film, it underwent a high-temperature annealing procedure within an air environment at 550 °C for a duration of two hours, leading to the development of a TiO2 film with a rutile phase.
The upper electrode employs a transparent conductive film composed of silver nanowires (AgNWs). For the AgNWs preparation, 1 ml of silver nanowire alcohol dispersion (with a concentration of 2 mg/ml and a diameter of 60 nm) was measured and introduced into a beaker. Subsequently, 2 ml of anhydrous alcohol was added for dilution. The mixture underwent 5 minutes of ultrasonic cleaning to ensure a homogeneous dispersion of AgNWs. Subsequently, the sample was positioned on a spin coater, and 0.5 ml of the prepared AgNWs dispersion was uniformly dropped onto the sample surface. The spin coater was subsequently programmed to rotate at 600 rpm for 10 seconds, followed by a 7000 rpm rotation lasting for 60 seconds. This procedure was duplicated once to achieve a decreased resistance. Lastly, the specimen was heated to 70 °C in ambient air for a duration of 10 minutes. As a consequence, a uniformly distributed, remarkably transparent, and highly conductive AgNWs film was achieved, constituting a transparent conductive grid.
3.2 Analysis instruments
A field emission scanning electron microscope (SU8020, Hitachi High-Technologies, Japan) was used to examine the morphology of the samples. The X-ray diffraction (XRD) spectra of the samples were measured using an X-ray diffractometer (SmartLab3 KW, RIGAKU, Japan). The ferroelectric hysteresis loops of the PZT/GaN sample were tested using a ferroelectric analyzer (TFA ANLYZER 2000E, AIXACCT, Germany). The atomic force microscope (AFM) and piezoresponse force microscope (PFM) were used to characterize the PZT film, and these measurements were performed with the Dimension Icon Scanasysty (Brook (Beijing) Technology Co., Ltd., Malaysia). The absorption coefficients of the PZT films were measured using a wide-spectrum Mueller matrix ellipsometer (ME-L, Wuhan YiguAng Technology Co., Ltd., China). A UV spectrophotometer (TU-1901, PERSEE, Beijing, China) was used to measure the optical transmission spectra. The valence band maximum X-ray photoelectron spectroscopy (VBM-XPS) of the PZT and GaN films was measured using X-ray photoelectron spectroscopy (Thermo Scientific K-Alpha,USA).
3.3 Photoelectric measurements
The photoelectric performances of the device were measured by using an oscilloscope (Tectronix MDO 3012, OH, USA), and an electrometer (Keithley Model 6514, OH, USA). The devices were polarized and tested for IV curves using a digital source meter (Keithley Model 2410, OH, USA). The responsivity and EQE of the device were measured by using a testing system of the photodetector (DSR-3110-PZ, Zolix, Beijing, China) with an ultraviolet-enhanced light source. The ultraviolet light source (WarSun R838) had a wavelength of 365 nm. The light power density was measured using a high-precision photonic laser power meter (PS100, CNI, China).
4. Conclusions
In this study, we employed p-GaN as a substrate to induce robust self-polarization effects in PZT that subsequently modulate the TiO2/PZT heterojunction and fabricated a self-powered UV photodetector featuring an AgNWs/TiO2/PZT/GaN structure. Its unique dual-coupling enhancement effect enables outstanding optical detecting performance. When illuminated by an optical power density of 0.013 mW/cm2, it exhibits an R of 184.31 mA/W and a specific D* of 1.71 × 1013 Jones. The rise/decay time of the device reaches 0.16 ms/0.98 ms, and the maximum on/off ratio reaches 8.1 × 106. Moreover, the device upholds rapid, reproducible, and stable detection detection performance even in strong light conditions. Benefitting from the dual enhancement of the self-polarization field and the built-in electric field, the photodetection performance of AgNWs/TiO2/PZT/GaN device surpasses those of conventional ferroelectric-based self-powered UV PD and makes a breakthrough. This strategy provides a practical approach for the advancement of high-performance self-powered optoelectronic devices.
Funding
National Natural Science Foundation of China (12364012, 62271362); Specific Research Project of Guangxi for Research Bases and Talents (Grant No. GUIKEAD22035178); Key Technology Research and Development Program of Shandong (2022CXGC020203).
Disclosures
The authors declare that there are no conflicts of interest related to this article.
Data availability
The data underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon reasonable request.
Supplemental document
See Supplement 1 for supporting content.
References
1. X. Xu, J. Chen, S. Cai, et al., “A real-time wearable uv-radiation monitor based on a high-performance p-CuZnS/n-TiO(2) photodetector,” Adv Mater 30, e1803165 (2018). [CrossRef]
2. X. Hu, X. Li, G. Li, et al., “Recent progress of methods to enhance photovoltaic effect for self-powered heterojunction photodetectors and their applications in inorganic low-dimensional structures,” Adv. Funct. Mater. 31(24), 2011284 (2021). [CrossRef]
3. L. Peng, L. Hu, and X. Fang, “Energy harvesting for nanostructured self-powered photodetectors,” Adv. Funct. Mater. 24(18), 2591–2610 (2014). [CrossRef]
4. D. Yuan, L. Wan, H. Zhang, et al., “An internal-electrostatic-field-boosted self-powered ultraviolet photodetector,” Nanomaterials (Basel) 12(18), 3200 (2022). [CrossRef]
5. W. Jiang, L. Liu, and J. Xu, “Improved detectivity and response speed of MoS(2) phototransistors based on the negative-capacitance effect and defect engineering,” Opt Express 30(26), 46070–46080 (2022). [CrossRef]
6. J. Chen, A. S. Priya, D. You, et al., “Self-driven ultraviolet photodetectors based on ferroelectric depolarization field and interfacial potential,” Sensors and Actuators A: Physical 315, 112267 (2020). [CrossRef]
7. A. L. Kholkin, K. G. Brooks, D. V. Taylor, et al., “Self-polarization effect in Pb(Zr,Ti)O-3 thin films,” Integr. Ferroelectr. 22(1-4), 525–533 (1998). [CrossRef]
8. Y. Zhang, X. Zhao, J. Chen, et al., “Self-polarized batio 3 for greatly enhanced performance of ZnO UV photodetector by regulating the distribution of electron concentration,” Adv. Funct. Mater. 30(5), 1907650 (2020). [CrossRef]
9. M. Wei, J. Hao, M. Liu, et al., “High-performance self-driven photodetectors based on self-polarized Bi0.9Eu0.1FeO3/Nb-doped SrTiO3 p-n heterojunctions,” J. Alloys Compd. 915, 165451 (2022). [CrossRef]
10. Z. Li, Y. Zhao, W. Li, et al., “Self-powered visible light photodetector based on BixFeO3 film,” Ceram. Int. 48(2), 2811–2819 (2022). [CrossRef]
11. L. Su, Z. Li, F. Cao, et al., “Tailoring the interface assembly of mesoporous TiO2 on BTO film toward high-performance UV photodetectors,” Journal of Materials Chemistry C 10(23), 9035–9043 (2022). [CrossRef]
12. S. M. Sadaf, E. Mostafa Bourim, X. Liu, et al., “Ferroelectricity-induced resistive switching in Pb(Zr0.52Ti0.48)O3/Pr0.7Ca0.3MnO3/Nb-doped SrTiO3 epitaxial heterostructure,” Appl. Phys. Lett. 100(11), 113505 (2012). [CrossRef]
13. Z. Liu, S. Zhang, Y. Zhi, et al., “Enhanced deep-ultraviolet sensing by an all-inorganic p-PZT/n-Ga2O3 thin-film heterojunction,” J. Phys. D: Appl. Phys. 54(19), 195104 (2021). [CrossRef]
14. B. Zhang, D. Tan, X. Cao, et al., “Flexoelectricity-enhanced photovoltaic effect in self-polarized flexible PZT nanowire array devices,” ACS Nano 16(5), 7834–7847 (2022). [CrossRef]
15. A. Davydok, T. W. Cornelius, C. Mocuta, et al., “In situ X-ray diffraction studies on the piezoelectric response of PZT thin films,” Thin Solid Films 603, 29–33 (2016). [CrossRef]
16. T. W. Cornelius, C. Mocuta, S. Escoubas, et al., “Piezoelectric response and electrical properties of Pb(Zr1-xTix)O3 thin films: The role of imprint and composition,” J. Appl. Phys. 122(16), 164104 (2017). [CrossRef]
17. S. Cheng, Z. Fan, L. Zhao, et al., “Enhanced photovoltaic efficiency and persisted photoresponse switchability in LaVO3/Pb(Zr0.2Ti0.8)O3 perovskite heterostructures,” Journal of Materials Chemistry C 7(40), 12482–12490 (2019). [CrossRef]
18. R. Vandana, M. Gupta, Tomar, et al., “Impact of TiO2 buffer layer on the ferroelectric photovoltaic response of CSD grown PZT thick films,” Appl. Phys. A 127(6), 427 (2021). [CrossRef]
19. S. K. Dey, W. Cao, S. Bhaskar, et al., “Highly textured Pb(Zr0.3Ti0.7)O3 thin films on GaN/sapphire by metalorganic chemical vapor deposition,” J. Mater. Res. 21(6), 1526–1531 (2006). [CrossRef]
20. L. Li, Z. Liao, M. Duc Nguyen, et al., “Epitaxial growth of full range of compositions of (1 1 1) PbZr1-Ti O3 on GaN,” J. Cryst. Growth 538, 125620 (2020). [CrossRef]
21. B. Peng, T. Wang, L. Liu, et al., “P-GaN-substrate sprouted giant pure negative electrocaloric effect in Mn-doped Pb(Zr0.3Ti0.7)O3 thin film with a super-broad operational temperature range,” Nano Energy 86, 106059 (2021). [CrossRef]
22. W. Cao, S. Bhaskar, J. Li, et al., “Interfacial nanochemistry and electrical properties of Pb(Zr0.3Ti0.7)O3 films on GaN/sapphire,” Thin Solid Films 484(1-2), 154–159 (2005). [CrossRef]
23. A. N. Khan, S. N. Mishra, S. Routray, et al., “Analytical modeling and simulation of lattice-matched Ferro PZT AlGaN/GaN MOSHEMT for high-power and RF/Microwave applications,” J. Comput. Electron. 22(3), 827–838 (2023). [CrossRef]
24. Y. Zhang, J. Chen, L. Zhu, et al., “Self-powered high-responsivity photodetectors enhanced by the pyro-phototronic effect based on a BaTiO(3)/GaN heterojunction,” Nano Lett 21(20), 8808–8816 (2021). [CrossRef]
25. J. Tauc, “Optical properties and electronic structure of amorphous Ge and Si,” Mater. Res. Bull. 3(1), 37–46 (1968). [CrossRef]
26. H. Kang, J. S. Kim, S.-R. Choi, et al., “Electroplated core–shell nanowire network electrodes for highly efficient organic light-emitting diodes,” Nano Convergence 9(1), 1 (2022). [CrossRef]
27. Y. S. Yun, D. H. Kim, B. Kim, et al., “Transparent conducting films based on graphene oxide/silver nanowire hybrids with high flexibility,” Synth. Met. 162(15-16), 1364–1368 (2012). [CrossRef]
28. A. Kumar, “Effects of annealed temperature on the properties of TiO2 thin films,” AIP Conf. Proc. 1731, 050064 (2016). [CrossRef]
29. L. C. Tănase, L. E. Abramiuc, D. G. Popescu, et al., “Polarization orientation in lead zirconate titanate (001) thin films driven by the interface with the substrate,” Phys. Rev. Appl. 10(3), 034020 (2018). [CrossRef]
30. A. V. Dixit, N. R. Rajopadhye, and S. V. Bhoraskar, “Secondary electron emission of doped PZT ceramics,” J. Mater. Sci. 21(8), 2798–2802 (1986). [CrossRef]
31. B. Y. Zhang, T. Liu, B. Meng, et al., “Broadband high photoresponse from pure monolayer graphene photodetector,” Nat Commun 4(1), 1811 (2013). [CrossRef]
32. J.-P. Wang, H. Mana-ay, C.-S. Chen, et al., “Enhanced UV photosensing properties by field-induced polarization in ZnO-modified (Bi0.93Gd0.07)FeO3 ceramics,” J. Alloys Compd. 902, 163779 (2022). [CrossRef]
33. J. Chen, Z. Wang, H. He, et al., “High-performance self-powered ultraviolet photodetector based on coupled ferroelectric depolarization field and heterojunction built-in potential,” Adv. Electron. Mater. 7(12), 2100717 (2021). [CrossRef]
34. L. Sun, C. Wang, T. Ji, et al., “Self-powered UV-visible photodetector with fast response and high photosensitivity employing an Fe:TiO2/n-Si heterojunction,” RSC Adv. 7(81), 51744–51749 (2017). [CrossRef]
35. M. Chen, X. Shen, C. Zhou, et al., “High-performance self-powered visible-blind ultraviolet photodetection achieved by ferroelectric PbZr0.52Ti0.48O3 thin films,” J. Alloys Compd. 897, 163208 (2022). [CrossRef]
36. B. D. Boruah, A. Mukherjee, and A. Misra, “Sandwiched assembly of ZnO nanowires between graphene layers for a self-powered and fast responsive ultraviolet photodetector,” Nanotechnology 27(9), 095205 (2016). [CrossRef]
37. L. Zheng, F. Teng, Z. Zhang, et al., “Large scale, highly efficient and self-powered UV photodetectors enabled by all-solid-state n-TiO2nanowell/p-NiO mesoporous nanosheet heterojunctions,” Journal of Materials Chemistry C 4(42), 10032–10039 (2016). [CrossRef]
38. H. Ma, L. Jia, Y. Lin, et al., “A self-powered photoelectrochemical ultraviolet photodetector based on Ti(3)C(2)T(x)/TiO(2)in situformed heterojunctions,” Nanotechnology 33(7), 075502 (2022). [CrossRef]
39. Z. Zhou, X. Li, F. Zhao, et al., “Self-powered heterojunction photodetector based on thermal evaporated p-CuI and hydrothermal synthesised n-TiO2 nanorods,” Opt. Mater. Express 12(2), 392–402 (2022). [CrossRef]
40. Q. Zhang, J. Xu, M. Li, et al., “High-performance self-powered ultraviolet photodetector based on BiOCl/TiO2 heterojunctions: Carrier engineering of TiO2,” Appl. Surf. Sci. 592, 153350 (2022). [CrossRef]
41. J. Chen, J. Xu, S. Shi, et al., “Novel self-powered photodetector with binary photoswitching based on SnS(x)/TiO(2) heterojunctions,” ACS Appl Mater Interfaces 12(20), 23145–23154 (2020). [CrossRef]
42. D. Wang, C. Huang, X. Liu, et al., “Highly uniform, self-assembled AlGaN nanowires for self-powered solar-blind photodetector with fast-response speed and high responsivity,” Adv. Opt. Mater. 9(4), 2000893 (2021). [CrossRef]
43. Y. Zhang, J. Chen, Q. Zhang, et al., “Ultrasensitive self-powered UV PDs via depolarization and heterojunction fields jointly enhanced carriers separation,” J. Am. Ceram. Soc. 105(1), 392–401 (2022). [CrossRef]
