Influence of Low Temperature-Grown GaAs on Lateral Thermal Oxidation of Al 0.98 Ga 0.02 As
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2 Department of Electrical and Computer Engineering, University of California, Santa Barbara, CA
ABSTRACT The lateral thermal oxidation process of Alo.98Gao.02As layers has been studied by transmission electron microscopy. Growing a low-temperature GaAs layer below the Alo.98Gao.02As has been shown to result in better quality of the oxide/GaAs interfaces compared to reference samples. While the later have As precipitation above and below the oxide layer and roughness and voids at the oxide/GaAs interface, the structures with low-temperature have less As precipitation and develop interfaces without voids. These results are explained in terms of the diffusion of the As toward the low temperature layer. The effect of the addition of a Si0 2 cap layer is also discussed. INTRODUCTION Lateral oxidation of AlxGal-,As layers is a very attractive technology for the fabrication of isolating oxide layers in optoelectronic devices because of their stability, high resistivity and near planar topology. They have been used in forming self-aligned dielectric layers in the fabrication of semiconductor laser diodes and on vertical cavity surface emitting laser (VCSEL) applications due to the excellent carrier confinement provided by the oxidized layer. These methodcan also be used attention in metal-oxide-semiconductor (MOS) devices. The high quality of the oxide is attributed to the formation of stable AIO(OH) and A12 0 3 compounds [1]. However some problems related to the excess As created during the process, and weakness of the oxide interfaces, due to structural changes in the AlxGal.-As layers, remain unsolved [2,3]. The influence of parameters, such as temperature, layer thickness or composition, on the oxidation process has been the subject of recent studies. In this work we study the structural changes resulting from the inclusion of a low-temperature (LT) GaAs layer. The effects of the presence of a LT-GaAs on the oxidation rates was reported previously [4] indicating a higher oxidation rate for samples including LT-GaAs layers. The influence of the incorporation of a SiO 2 capping layer on the quality of the oxide layer is also discussed. EXPERIMENTAL Samples were grown by molecular beam epitaxy (MBE) on a (100) semi-insulating GaAs substrate. Two similar structures (shown in Fig.l) were grown to be oxidized. The only difference between the two types of sample is that in one the central 300 nm thick layer is standard GaAs grown at 580°C whereas in the other sample it is low temperature GaAs, grown at 210'C. The low temperature GaAs was annealed at 600*C for two minutes in-situ and received further annealing during growth of the subsequent layers at 590°C: 100 nm of n-GaAs(Si:10s cm' 3), 30 nm of A10.98Ga0.02As, and a capping layer of 35 nm GaAs. In addition thin layers (0.510nm) of AlAs were grown on either side of the LT. The reference and the LT samples were processed simultaneously. Mesas were formed in the top of the samples by patterning and 407 Mat. Res. Soc. Symp. Proc. Vol. 623 © 2000 Materials Research Society
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