Role of C, O and H in III-V Nitrides
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precursors [(C2H5)3Ga and NH 3] and the ambient. Past work has shown that C has a deep acceptor level in the gap and is an ineffective dopant,•) although recent theoretical studies suggest it may have utility. (2) There has been one report of p-type GaN grown by Metal Organic Molecular Beam Epitaxy (MOMBE) in which the hole density increased with CC14 flow, but a completing parasitic etching reaction by 7 the 3 chlorine reduced the growth rate severely and a maximum hole concentration of -3x10' cm- was achieved.(3) Oxygen has been ascribed by some workers to be responsible for at least part of the residual n-type doping in most GaN, (4 although others suggest this is due to nitrogen vacancies. Hydrogen is of course important for its role in passivating the electrical activity of Mg acceptors in GaN grown by Metal Organic Chemical Vapor Deposition. Both e-beam irradiation or simple thermal annealing are found to restore the electrical activity of the Mg by dissociating the neutral Mg-H complexes. We have also recently found that forward bias injection of minority carriers in hydrogenated GaN p-n junctions can reactivate the Mg acceptors, a phenomenon that has also been observed for passivated B in Si and S donors in GaAs. In this paper we report on some experiments in which C, 0 or H have been introduced into GaN and related materials by implantation or diffusion and the effects on the electrical properties of the material measured. 685 Mat. Res. Soc. Symp. Proc. Vol. 395 01996 Materials Research Society
EXPERIMENTAL The nitrides employed in this work were prepared in a Varian Gas Source Gen II system fitted with a Wavemat MPDR 610 ECR plasma source.18 The nitrogen beam was generated using 200W forward power and nitrogen flows of 1-20 sccm. All layers grown on A12O3 contain an initial 500oA low temperature AIN buffer grown at 425°C using 1 sccm N2 flow. Triethylgallium III (TEG) was used as the Ga source, trimethylamine alane (TMAA) and dimethylamine alane (DMEAA) were used as the Al sources, and trimethylindium (TMI) and triethylindium (TEl) were employed as In sources. Some samples were implanted with C÷ or O÷ ions at typical energies of 100keV and doses of 1014-1015cmz followed by annealing up to 1100°C under a flowing N2 ambient in an RTA system. Hydrogen was introduced by exposing the samples to either a 1H or 2H ECR discharge for 30 mins at 250-400°C. Carrier densities and mobilities were obtained from van
der Pauw geometry Hall measurements using alloyed Hgln contacts and impurity profiles obtained from Secondary Ion Mass Spectrometry (SIMS) measurements performed at Charles Evans and Associates. RESULTS AND DISCUSSION (a)Carbon We find that InxGai~xN and InxAllixN alloys grown by MOMBE are strongly n-type for x > 0.15 (InGaN) and x > 0.3 (InA1N), with steadily decreasing conductivity as the In concentration is decreased. High electron concentrations have also been reported for InN grown by other methods,(9 and are usually ascribed to the presence of N vacancies, although this seems less likely in light of
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