Metalorganic Chemical Vapor Deposition of High Quality GaAs and AlGaAs Using Tertiarybutylarsine
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METALORGANIC CHEMICAL VAPOR DEPOSITION OF HIGH QUALITY GaAs AND AlGaAs USING TERTIARYBUTYLARSINE
G. HAACKE, S. P. WATKINS, H. BURKHARD, C. J. CALBICK AND J. QUICK American Cyanamid Company, Chemical Research Division, Stamford, CT 06904 ABSTRACT This paper discusses recent improvements achieved in the growth of epitaxial layers of GaAs and AlGaAs using the liquid arsine substitute tertiarybutylarsine (TBA) and metal alkyls. The high purity TBA now available yfjlds 3 undoped GaAs with residual donor/acceptor concentrations in the low 10 cm range. Under optimized growth conditiorp the layers are either n-type and have 77*K mobilities up to 85,000 cm /Vs or they are compensated or p-type. For aluminum gallium arsenide, layers grown with TBA have properties similar to arsine-grown material as demonstrated by low temperature photoluminescence (PL). The PL efficiencies and line widths of the TBA-grown AlGaAs samples are comparable to those prepared with arsine. INTRODUCTION Over the past few years work has been in progress to find a safe replacement for arsine widely used in metalorganic chemical vapor deposition (MOCVD) and other semiconductor processes [11, [2]. Tertiarybutylarsine has emerged as the leading candidate because it is liquid at room temperature and has a convenient vapor pressure for MOCVD operations. Furthermore, TBA was recently used to grow und~ped epitaxial GaAs in which liquid nitrogen mobilities up to 80,000 cm /Vs were achieved [3]. The dominant residual donor in these layers was identified by magnetophotoluminescence (MPL) as sulfur. Still higher purity TBA has now been produced [4] enabling us to grow the GaAs and AlGaAs discussed in this paper. EXPERIMENTAL RESULTS The epitaxial layers were grown at atmospheric pressure in a vertical 3" diameter quartz reactor described previously [3]. Trimethylgallium (TMG) and trimethylaluminum (TMA) were used as metal sources. The substrates were undoped, semi-insulating GaAs wafers oriented with 2° off toward . Hall measurements were made with dc current using the Van der Pauw method. The optical measurements were performed with the equipment discussed in References 3 and 5. Gallium Arsenide The conditions for the GaAs growth experiments reported in this paper were chosen to achieve high purity and keep the incorporation of background donors and acceptors at a minimum. We employed substrate temperatures of (.-600C) and V:III ratios of about 30:1. The principal donor identified by PL or MPL was sulfur. Germanium donors were seen to a lesser extent and only in samples grown at high V:III ratios and high substrate temperatures. The acceptors were zinc, originating from the trimethylgallium, and carbon. In agreement with earlier publications [6] zinc incorporated preferentially at low substrate temperatures while carbon was favored at higher temperatures and lower V:III ratios [7]. Mat. Res. Soc. Symp. Proc. Vol. 145. 01989 Materials Research Society
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The gallium arsenide samples reported earlier by us [3] were grown with TBA containing residual sulfur sp
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