Ion implantation and diffusion of Zn in GaAs

Abstract

Zn implantation (dose 5×1015 cm−2) and subsequent diffusion were carried out on GaAs wafers and on liquid-phase epitaxial GaAs layers. A silicon nitride cap was deposited by chemical vapor deposition (CVD) or by sputtering either before or after implantation. Profiles were determined with Secondary Ion Mass Spectrometry and Differential Hall Effect measurements and damage was studied with Rutherford Backscattering Spectrometry. Annealing gave rise to Zn segregation at the surface or just below it and at a depth past the implantation maximum. The diffusion was much deeper and the damage recovery was much less with implantation through a nitride layer than with implantation directly into GaAs. This is explained in terms of recoil implantation of Si and N and of a smaller Ga vacancy concentration so that less trapping of interstitial Zn by such vacancies takes place. Surface segregation of Zn and differences in diffusion depth between samples with sputtered and CVD silicon nitride caps are ascribed to the effects of stress. Except in a surface layer, complete electrical activation and ideal Hall mobility values were found after annealing at 700 °C.