The Role of Arsine in Reducing Carbon in Triethylarsenic Grown GaAs Films
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THE ROLE OF ARSINE IN REDUCING CARBON IN TRIETHYLARSENIC GROWN GaAs FILMS D.M. SPECKMAN AND J.P. WENDT The Aerospace Corporation, Electronics Research Laboratory, P.O. Box 92957, Los Angeles, CA 90009 ABSTRACT Very high carbon impurity levels (101 8-1021cm- 3) in GaAs films grown using triethylarsenic (Et3 As) and trimethylgallium (Me3Ga) can be dramatically reduced by substituting a portion of the Et3 As reagent with arsine during growth. Gallium arsenide epilayers grown at a deposition temperature of 5601C, a total V/Ill ratio =10, and the Group V reagent consisting of a mixture of Et3As and arsine, were found to exhibit carbon levels of only 5-7x10 15 cm-3 for Group V mixtures ranging from 0-65% Et3As. All of these films were n-type, except for those grown using 100% arsine, which were p-type. The reduction in carbon incorporation in films grown using Et 3 As and arsine as co-reagents is shown to result from a unique, synergistic, reaction chemistry involving the two arsenic reagents. In particular, the decomposition of arsine to provide carbon-free, active arsenic fragments for growth is greatly enhanced by the presence of Et 3 As as a co-reactant. INTRODUCTION There has been a significant effort recently to develop alternative OMCVD arsenic reagents for their use in the growth of superior GaAs films under less hazardous conditions than are currently found for conventional arsine/trimethylgallium (AsH 3 /Me3Ga) growths. Organoarsines show promise as safer alternatives to the use of arsine, but many of those tested produce films which are heavily contaminated with carbon [1]. Our laboratory has shown that GaAs epilayers grown from triethylarsenic (Et3As) and Me3Ga contain very high levels of carbon impurities (1018 -1021cm- 3) [2]. This carbon doping appears to be related to the inherent growth chemistry of the organoarsenic reagent, although the manner in which this occurs is speculative, since very little is actually known about the decomposition pathways of this reagent. Our laboratory has also previously shown that the Et3As/Me 3 Ga growth system can be manipulated to reduce the carbon contamination in resultant GaAs films; the carbon levels in Et3As/Me3Ga-grown films can be reduced to -mid-10 15 cm- 3 by the addition of arsine to the reaction mixture in a 1:1 molar ratio to the Et 3 As reagent [3]. We report here the results from our current investigations to determine the mechanism by which the carbon is incorporated into Et3As/Me3Ga-grown GaAs films, and by which it is reduced in the GaAs films grown from Et 3 As and AsH 3 arsenic co-reagents. GROWTH STUDIES Two distinct growth mechanisms were considered to be likely candidates for causing the reduction in carbon incorporation in Et 3 As/AsH3-grown films compared with Et3As-grown epilayers. The first possibility was that the Et 3 As and AsH 3 each simply compete within the growth chamber for reaction with Me3Ga, with the growth chemistry of each arsenic reagent operating independently of the growth chemistry of the other arsenic reagent. Since the carbon
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