The diffusion of Si was studied in <100> GaAs which had been implanted with 40keV 30Si+ ions to a dose of 1016/cm2. The Si concentration profiles were determined by means of secondary-ion mass spectrometry and nuclear resonance broadening techniques, and the defect distributions were determined by using the Rutherford back-scattering spectrometry channelling technique. The implanted samples were subjected to annealing in Ar at temperatures ranging from 650 to 850C (table 1). Two independent Si diffusion mechanisms were observed. It was found that concentration-independent diffusion, seen as a broadening of the initial implanted distribution, was very slow and was attributed to Si atoms that diffused interstitially. A concentration-dependent diffusivity with low solubility, which extended deeply into the sample, was quantitatively explained in terms of diffusion, via vacancies, of Si atoms on the Ga and As sub-lattices (figure 4). Diffusion coefficients, together with the carrier concentration as a function of Si concentration, were obtained at various temperatures. The concentration-independent diffusion of Si was described by:

D (cm2/s) = 1.23 x 10-7 exp[-1.72(eV)/kT]

The solid solubility of Si in GaAs was determined, and an exponential temperature dependence was observed. An estimate was made of the numbers of Si atoms which resided on the Ga and As sites, and the number of SiGa+-SiAs- pairs was deduced. The intrinsic diffusivities via neutral Ga vacancy complexes, triply negatively charged As vacancy complexes and triply negatively charged Ga vacancy complexes were:

D (cm2/s) = 3.74 x 10-3 exp[-2.60(eV)/kT]

D (cm2/s) = 4.67 x 10-5 exp[-2.74(eV)/kT]

and

D (cm2/s) = 5.92 x 10-8 exp[-2.28(eV)/kT]

respectively.

T.Ahlgren, J.Likonen, J.Slotte, J.Räisänen, M.Rajatora, J.Keinonen: Physical Review B, 1997, 56[8], 4597-603

Table 1

Diffusivity of Si in GaAs

Figure 4

Diffusivity of Si in GaAs, as Mediated by Various Vacancy-Types