Diffusion and Electrical Properties of Sulfur Implanted in Gallium-Arsenide

94 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1983.The diffusion and electrical properties of implanted sulfur in GaAs have been investigated with secondary ion mass spectrometry (SIMS) and differential resistivity and Hall measurements. Low dose (7 x 10('12) cm('-2), 250 keV) S implants exhibit redistribution behavior upon annealing which approximates gaussian diffusion. Diffusion coefficients estimated from the tails of annealed profiles are high: 9 x 10('-13) cm('2)/sec, 1 x 10('-12) cm('2)/sec and 8 x 10('-12) cm('2)/sec for 700(DEGREES)C, 800(DEGREES)C and 900(DEGREES)C respectively. The mechanism is believed to be due to defect enhanced diffusion, since these values considerably exceed those reported for S indiffusion into crystalline GaAs. Increasing the implantation dose decreases the diffusivity of S around the peak of the profile, but penetrating tails are still formed. For electrical measurements, type conversion of the Cr-doped substrates used in this study limits the annealing temperature to 800(DEGREES)C. At this temperature, the electrical activation is at best fair for the low (7 x 10('12) cm('-2), 250 keV) and medium (7 x 10('13) cm('-2), 250 keV) doses, being 26% and 36% respectively. Overall activation efficiency is low (2.3%) for high dose (10('15) cm('-2), 250 keV) implants, and although the SIMS profiles reveal little diffusion and a very high S concentration around the original as-implanted peak, almost all of the S in this region is electrically inactive.The diffusivity of implanted S has been found to be reduced in the presence of a sufficient level of Si doping, whether the latter is introduced during crystal growth or by co-implantation. The reduction is observed up to an annealing temperature of 800(DEGREES)C. However, at 900(DEGREES)C thermal processes again prevail. Dual implants of S and Si have been found to give substantial improvements in peak carrier concentration and activation efficiency as compared to Si implants of an equivalent dose.Low levels of implantation damage, as produced by 3.5 x 10('13) cm('-2), 250 keV Ar co-implants, have been found to result in damage enhanced diffusion of S upon annealing. In the presence of amorphizing Ar co-implants, however, little diffusion is observed up to 900(DEGREES)C. Unfortunately, the electrical activity of the implanted S is entirely lost at the same time. There is some evidence that thermally stable but electrically inactive S-defect complexes are formed which do not diffuse.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD