CONCENTRATION-DEPENDENT ZN DIFFUSION IN INP DURING METALORGANIC VAPOR-PHASE EPITAXY

Concentration dependent diffusion of Zn during metalorganic vapor phas e epitaxy from a Zn-doped InP layer into the adjacent undoped InP buff er layer were studied systematically using secondary ion mass spectros copy and carrier concentration profiling. Under the condition that the growth rate of the Zn-doped film is faster than the interdiffusion of Zn into the underlying undoped buffer layer, the diffusion problem ca n be treated as a one-dimensional diffusion couple between two semi-in finite media. Furthermore, Zn diffusion during the optimized growth co ndition for InP completely eliminates the thermal decomposition proble m encountered in the sealed ampoule and open tube diffusions and also maintains all the intrinsic point defects at their thermodynamic equil ibrium concentrations. With an optimal growth temperature at 625 degre es C and a maximum Zn flow below the incorporation limit for substitut ional Zn to ensure that the dominant Zn are incorporated substitutiona lly, the diffusion profiles of Zn across the interface in this simple and clean system are simulated using a concentration dependent diffusi vity. A third power concentration dependence of the effective diffusio n coefficient has been confirmed, which applies to both Frank-Turnbull and kickout interstitial-substitutional equilibrium mechanisms using an interstitial-substitutional diffusion model. This indicates a +2 ch arge state of the fast diffusing Zn interstitials. The extrapolated cu rve into high-concentration diffusion source regime used by sealed amp oule diffusion experiments generally agrees with the published results although the dominant Zn atoms found in the high-concentration diffus ion source regime form complexes with phosphorous vacancies in a neutr al state. The enhanced diffusion due to excess interstitials is discus sed. (C) 1995 American Institute of Physics.