Alkoxide Doping of GaAs During Organometallic Vapor Phase Epitaxy
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ALKOXIDE DOPING OF GaAs DURING ORGANOMETALLIC VAPOR PHASE EPITAXY Y. PARK*, M. SKOWRONSKI* AND T. M. ROSSEEL** *Department of Materials Science and Eng., Carnegie Mellon University, Pittsburgh, PA 15213 **Oak Ridge National Laboratory, Oak Ridge, TN 37831 ABSTRACT Doping of GaAs with dimethylaluminum methoxide and its effects have been studied during metalorganic vapor phase epitaxy. Oxygen concentration decreases exponentially with increasing growth temperature and the activation energy equal to 1.8 eV. Increase of oxygen content with decrease of V/III ratio indicates that oxygen most likely occupies arsenic site. Photoluminescence intensity was observed to decrease with increasing oxygen content and three new deep level luminescence peaks appeared at 75, 96, and 160 meV below the band gap. This, together with the fact that as-grown layers are fully depleted, indicates that oxygen is electrically active in OMVPE GaAs and forms deep non-radiative recombination centers. INTRODUCTION Oxygen is one of the most persistent contaminants in virtually all semiconductors and in particular in compounds containing aluminum. For many years the performance of OMVPE and MBE deposited AlGaAs lasers and Light Emitting Diodes has been consistently inferior to that of devices grown by LPE probably because of oxygen incorporation. There are numerous sources of possible contamination: traces of water and oxygen in arsine cylinders, leaks in the OMVPE system, oxygen adsorbed at walls of MBE apparatus, traces of oxides in gallium source in MBE, but the most important one appears to be the presence of alkoxides in the most commonly used metalorganic aluminum sources: (CH 3 ) 3 AI and (C 2H 5) 3AI.1 Number of 2 attempts have been made at simulating oxygen contamination by controlled leaks of oxygen -4 56 and recently by intentional doping with dimethylaluminum methoxide. . The results of oxygen incorporation are usually detrimental to the layer quality. The 7 presence of even traces of oxygen in material leads to the decrease of luminescence intensity -11 2 and lowering of solar cell efficiency.1 This effect has been interpreted as due to formation of oxygen-related deep nonradiative recombination centers. It has also been observed that
oxygen incorporation leads to compensation of shallow donors making AlGaAs layers semi14 This observation led to application of insulating'- 3.' 3 and decreasing electron mobility. 15 16 Other potential oxygen compensated layers for gate isolation in GaAs FET structures. . applications of oxygen doped semiconductor layers are buffer layers for device isolation,
surface passivation, and active layers in ultrafast photoconductive switches. EXPERIMENTAL PROCEDURE GaAs epilayers were grown on semi-insulating (100) GaAs substrates using trimethylgallium (TMG) and tertiarybutyl arsine (TBA). TBA was at 2 OC with typical H2 flow of 50 sccm while TMG bubbler was maintained at -15 OC with hydrogen flow of 10 Mat. Res. Soc. Symp. Proc. Vol. 282. Q1993 Materials Research Society
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sccm. This flow rate correspon
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