Stepwise Monolayer Growth of GaAs by Pulsed Laser Metal Organic Vapor Phase Epitaxy
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STEPWISE MONOLAYER GROWTH of GaAs by PULSED LASER METAL ORGANIC VAPOR PHASE EPITAXY Atsutoshi Doi, Yoshinobu Aoyagi, and Susumu Namba The Institute of Physical and Chemical Research Wako-shi, Saitama, 351-01, Japan ABSTRACT Atomic layer epitaxy (ALE) of GaAs by pulsed laser metal organic vapor phase epitaxy is reported. Suspension of Ga deposition at 100% coverage is an essential part of the growth mechanism for ideal ALE. This is achieved by a photo-catalytic decomposition of adsorbed trimethylgallium (TMG). Selective enhancement of the decomposition rate for adsorbed TMG on As, with no enhancement for that on Ga is the main reason for suspension of Ga deposition at 100% coverage. A decomposition rate for TMG on As which is about 100 times faster than that on Ga is estimated from a comparison between theory and experiment. INTRODUCTION There is growing interest in atomic layer epitaxy (ALE) of the GaAs/GaAlAs system since this technique seems to be a promising candidate for producing thin epitaxial layers and abrupt interfaces. Ideal ALE of GaAs/GaAlAs would be achieved by successively depositing a monolayer of Ga/Al followed by a monolayer of As atoms. Therefore the interfaces, in principle, would be atomically abrupt and the layer thickness could be controlled with an accuracy of one monolayer. In order to realize ideal ALE, a means of arresting deposition at 100 % surface coverage needs to be an essential part of the growth mechanism. Recently, ALE of GaAs has been reported[1-4]; however, the ideal growth rate of one monolayer/cycle has been very difficult to achieve. The difficulty most likely arises from the growth process which has no or weak mechanism of arresting deposition at 100% coverage. If we can introduce a strong surface reaction-limited growth mechanism, then ideal ALE would be realized. Argon ion laser irradiation is a candidate to enhance the surface reactions [5]. In this paper, we describe a new ALE method for depositing GaAs using the pulsed laser metal organic vapor phase epitaxy (MOVPE). The strong surface reaction-limited growth was achieved by Ar÷ laser irradiation and the ideal growth rate of one monolayer per cycle was realized [6]. The surface reactionlimited growth model is analyzed and the results are compared with those from experiments. It is found that selective enhancement of the decomposition rate for adsorbed TMG on As by Ar+ laser irradiation is the main reason why Ga deposition is suspended at 100% coverage. THEORY The idea of using monolayer adsorption by a compound source gas followed by reaction to deposit a semiconductor film has been reported by T. Suntola [7]. If there were no steric hindrance around the alkyl group, no desorption, and no Mat. Res. Soc. Symp. Proc.Vol.75. 1987 Materials Research Society
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decomposition of adsorbed metal organics in the pulsed MOVPE of GaAs, then ideal ALE layer growth would be easily achieved by the adsorption and reaction mechanism. It seems an over simplification to omit these surface processes for analyzing decomposition of TMG a
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