Abstract

We demonstrate the first intersubband detectors in the 3-5 μm mid-infrared band using bound to continuum state absorption in InGaAs/InAlAs multiquantum well (MQW) structures. These detectors are background limited at temperatures below 120K with a ${\text{D}}_{\text{BL}}^{*}=2.3\times {10}^{10} \text{cm}\sqrt{\text{Hz}}/\text{W}$ for a 180° field of view. Photo-detectors with broad spectral response peaked at 4 μm showed good optical gain, low dark current and high detectivity. A MQW structure consisting of 50-periods of 30 Å In_0.53Ga_0.47As quantum wells (doped n = 2×10¹⁸ cm^-3) and 300 Å undoped In_0.52Al_0.48As barriers was grown by molecular beam epitaxy on Fe-doped InP substrates. The measured absorption spectrum of this sample at room temperature is peaked at 279 meV (λ = 4.44 µm) with a full width at half maximum (FWHM) of 93 meV. We obtained the broad 33% linewidth covering the full 3-5 µm band by pushing the excited state higher up into the continuum. The noise measured in the MOW detectors is limited by the shot-noise of the dark current, which, for typical 200 µm mesa detectors, is determined by thermally assisted tunneling through the thick barriers. The peak detectivity of this 4 µm detector at 77K is thus ${\text{D}}_{\lambda }^{*}=1.5\times {10}^{12} \text{cm}\sqrt{\text{Hz}}/\text{W}$.

© 1989 Optical Society of America