Concentration dependent and independent Si diffusion in ion-implanted GaAs

The diffusion of silicon has been studied in [100] GaAs implanted with 1x10(16) 40-keV Si-30(+) ions/cm(2). The Si concentration profiles were measured by secondary-ion mass spectrometry and nuclear resonance broadening techniques and the defect distributions by the Rutherford backscattering spectrometry channeling technique. The implanted samples were subjected to annealing in argon atmosphere in the temperature range 650 degrees C-850 degrees C. Two independent silicon diffusion mechanisms were observed. Concentration independent diffusion, observed as a broadening of the initial implanted distribution, is very slow and is assigned to Si atoms diffusing interstitially. Concentration dependent diffusion with low solubility and extending deep into the sample is quantitatively explained by diffusion via vacancies of Si atoms in the Ga and As sublattices. Diffusion coefficients together with carrier concentration as a function of Si concentration are given at different temperatures. The solid solubility of Si in GaAs has been determined and an exponential temperature dependence observed. An estimate of the amount of Si atoms residing on either Ga or As sites and the amount of Si-Ga(+)-Si-As(-) pairs is given. Finally, a fast method is presented for solving the diffusion equation numerically.