A New Approach for Heavy N-Doping Process in Ge Epilayers Using Specific Solid Source

Abstract

As an indirect band gap material, Germanium (Ge) has low efficiency of radiative recombination in the wavelength area of about 1550 nm. However, the difference between the direct and indirect band gap is very small (~140 meV) and photoluminescence emission ability of Ge could be greatly enhanced by heavy n-doping process. In this work, Ge growth directly on Si (001) substrate by molecular beam epitaxial (MBE) technique and a high n-doping level in Ge was obtained owning to using GaP decomposition source. The GaP solid source produces P 2 molecules instead of P 4 molecules, which have higher sticking coefficient than that of P 4 comparing to the traditional doping method from PH 3 gas precursor molecules. The dependence of optical property on Ge film thickness is also studied. The out-diffusion phenomenon of phosphorus dopant has been observed through SIMS profile analysis. An activated phosphorus concentration can be achieved up to more than 2 × 10 19 atoms•cm −3 confirmed by Hall effect measurement. This result contributes to realization of Ge-on-Si devices for optoelectronic applications.