Abstract
Recent progress of III-V compounds grown by ALE was mainly focused on binary alloys with very little activity on ternary alloys. This has limited the usefulness of ALE in the growth of heterojunction device structures. We report the ALE growth of Al(x)Ga1-xAs (0 < x < 0.4) and AlGaAs/GaAs quantum wells. The ALE growth cycle consisted of the simultaneous exposure of the substrate to the TMGa and TMAl fluxes followed sequentially by an AsH3 exposure. Atomic layer epitaxy was carried over a temperature range from 550 to 700-degrees-C, and monolayer growth was only observed over a fairly narrow range of column III flux. Al incorporates during ALE film growth more efficiently than during MOCVD growth in the same reactor. The ALE films show better composition uniformity than the MOCVD ones. AlGaAs/GaAs quantum wells were also grown solely by ALE at the same temperature with very uniform well thickness. High quality ALE grown GaAs was achieved. Background carrier concentration in 10(14)-10(15) cm-3 range was obtained with 77 K mobility about 30,000 cm2/V.s for 2 mu-m thick films. The 4 K photoluminescence displayed well resolved bound excitonic transitions characteristic of high purity GaAs. The material quality improved with increasing V/III ratio and growth temperature.