Abstract
This work concerns with the use of Germanium Arsenide (GeAs) as a vapor source for the diffusion of Ge into GaAs substrates and GaAs/AlxGa1-xAs heterostructures. The GeAs crystal was synthesized using the sealed quartz ampoule technique, and it is found that during synthesis the cooling rate plays a key role to the composition and structure of the Germanium Arsenide end product. The germanium diffusion depth varies greatly depending on the doping concentration of the substrate, the aluminum content in the AlGaAs layer, the annealing temperature and time. The diffusion coefficients of Ge in the semi-insulating GaAs (SI-GaAs) are estimated to be D≒1.1*10-12(cm2/s) at 800oC and D≒6.79*10-14(cm2/s) at 750oC, respectively. The diffusion coefficients of Ge in p+-GaAs are estimated to be D≒4.66*10-13 (cm2/s) at 800oC and D≒3.07*10-14 (cm2/s) at 750oC, respectively. The reduction of diffusion rate with the P-type doping is believed to be governed by the Fermi level effect. Moreover, Ge diffuses even slower as the Al content increase from 0%, 32% to 46%, and we attribute it to the increase in lattice strain. Finally, the photoluminescence spectra of the GaAsP/AlxGa1-xAs heterostructure diffused with Ge at 800oC for various times have shown a trend of red shift suggesting Column Ⅴ sites intermixing is the favored diffusion mechanism when GeAs is used as the diffusion source.