DIFFUSION OF ZN INTO GAAS AND ALGAAS FROM ISOTHERMAL LIQUID-PHASE EPITAXY SOLUTIONS

In this work we present results of zinc diffusion in GaAs using the liquid phase epitaxy technique from liquid solutions of Ga-As-Zn and Ga-As-Al-Zn. Using silicon-doped n-GaAs substrates, working at a diffusion temperature of 850 °C, and introducing a dopant concentration ranging 1018-10 19 cm-3, the most important findings regarding the diffusion properties are as follows: (a) zinc concentration in the solid depends on the square root of zinc atomic fraction in the liquid; (b) the diffusion is dominated by the interstitial-substitutional process; (c) the diffusivity D varies as about C3 in the form D=2.9×10-67C 3.05; (d) aluminum plays the role of the catalyst of the diffusion process, if it is introduced in the liquid solution, since it is found that D varies as (γAsXl As)-1; (e) the zinc interstitial is mainly doubly ionized (Zn++ i); (f) the zinc diffusion coefficient in Al0.85 Ga0.15 As is about four times greater than in GaAs; (g) by means of all these results, it is possible to control zinc diffusion processes in order to obtain optimized depth junctions and doping levels in semiconductor device fabrication.