Abstract

The quaternary alloy of InGaAlAs lattice matched to InP substrate is a promising material for electronic and optoelectronic device applications.¹ From the growth point of view the alloy is relatively easier to grow by molecular beam epitaxy (MBE) compared to the more popular quaternary alloy of InGaAsP.² In this work we have systematically doped the InGaAlAs quaternary alloy with silicon at various doping levels and observe the limits of electron concentration and mobility. The heavily doped n-InGaAlAs epilayers have been usefully incorporated as emitters in HBT devices.³ The characterization tools essentially used are the double crystal x-ray diffraction (DCXD) for lattice matching, Hall measurements for the doping and mobility determination and Photoluminescence for the optical quality of the layers. The epitaxial layers were grown in a RIBER 32P MBE system with 6 N purity elements and high levels of vacuum in the chamber. The starting samples were of n-type (si-doped) and semi-insulating (Fe-doped) InP substrates from Sumitomo Co. The epitaxial layers grown were all closely matched to the InP substrate with lattice mismatch less than 4.0 E-4 and DCXD peaks with half widths in the range of 20-35 sec. In Fig. 1 DCXD plot of a sample of carrier concentration 2.0E17 cm^-3 is shown with the characteristic hump in the peaks being to the dis-similar first (GaAs) and second (sample) crystals, in the x-ray system. Doping levels from 8.0E15 to 2.0E19 cm^-3 and mobilities in the range 1640 to 600 cm²/V-sec. were obtained for the variation of silicon cell temperature from 975 to 1150°C. In Fig. 2, a comparison is made between the experimentally observed mobility values of In_0.53Ga_0.08Al_0.39As alloy and the values reported for the ternary alloys of InGaAs and InAlAs.⁴ The mobility behavior is intermediate of the two ternary alloys, suggesting that it is pseudo-binary alloy. Mobility measurements taken at different substrate temperatures (100 to 400 K) showed no significant enhancement in the magnitudes though theoretical calculations made by using the expression for limits on alloy scattering⁵ indicate close agreement with the experimental values as shown in Fig. 3. Photoluminescence profile at room and 5 K temperatures have showed luminescence peaks at 920 nm and 880 nm with half widths of 90 and 12 meV respectively. From the above data, the crystalline and optical quality of the epilayers is of the state-of-the-art work reported on this material.

© 1995 IEEE