XPS and AES Studies of the Initial Stage of CdTe Growth on (100) GaAs by MOVPE
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XPS AND AES STUDIES OF THE INITIAL STAGE OF CdTe GROWTH ON (100) GaAs BY MOVPE MITSURU
EKAWA,
KAZUHITO YASUDA, SYUJI SONE, YO$HIYUKI SUGIURA, MANABU SAJI AND AKIKAZU TANAKAV Dept. of Electrical and Computer Engineering, Nagoya Institute of Technology, Showa, Nagoya 466, JAPAN * Electronics Materials Laboratory, Sumitomo Metal Mining Co., Ltd., Ohme, Tokyo 198, JAPAN
ABSTRACT XPS and AES analyses were performed to investigate the initial growth mechanism and the selection of the growth orientations of CdTe layers grown on (100) GaAs substrates by MOVPE. The (100) CdTe growth was reproducibly achieved when the GaAs surface was completely covered by one monolayer of Te before the growth, otherwise (111) growth occurred.
INTRODUCTION The epitaxial growth of CdTe and HgCdTe on (100) GaAs substrates is attractive since this system is promising for the large-scale integrated infrared detectors [1,2]. HgCdTe is also considered as a suitable material for an extremely low noise avalanche photodiode for lightwave communications in the 1.3-1.55 pm wavelength region [31. Metalorganic vapour phase epitaxy (MOVPE) and molecular beam epitaxy (MBE) have been the major growth techniques to realize such systems. However, it is found that the growth can proceed in two different growth orientations of (100) and (111) due to a large lattice mismatch (ov15%) between GaAs substrate and the grown layer [471. For the applications of HgCdTe photodiodes, (100) HgCdTe layers are preferable because (111) layers contain twin boundaries which deteriorate the device characteristics. The growth of (100) CdTe buffer layer enables the (100) HgCdTe growth. It is, therefore, required to control the growth orientations of CdTe layers on GaAs. The selection of the growth orientations has been extensively studied in MBE, and several mechanisms have been proposed. It has been suggested that (100) growth occurs when an oxide remains on the GaAs surface [8-10]. The adsorption of Te on the GaAs surface has also been considered to be a factor influencing the CdTe orientation [1113]. In MOVPE, however, littl effort has been devoted to clarify the initial growth mechanism. We performed XPS and AES analyses of (100) GaAs surface structures at each stage of the pretreatment procedures to clarify the initial growth mechanism of CdTe layers by MOVPE. The variations of GaAs surface structures in MOVPE process are definitively discussed. The key to controlling the orientations of CdTe layers is also clarified.
EXPERIMENTAL PROCEDURES CdTe growth was carried out in a low-pressure MOVPE system operating at 60 Torr. The precursors used were dimethylcadmium (DMCd) and diethyltelluride (DETe), which were delivered to the growth reactor using Pd-diffus d H2 as a carrier gas. The flow rates of DMCd and DETe were 2xlO and 8xlO mo /min, respectively. In this study, n+-(l00) GaAs was used as the substrate. After degreasing, the substrates were etched in a solution of 5:1:1 H2 SO4 :H2 0 2 :H2 0 for 5 min and rinsed with deionized water. Prior to growth, these substrates wer
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