In Situ Phosphorus Doping of Germanium by APCVD

Abstract

The in-situ fabrication of rectangular concentration-depth profiles of phosphorus in germanium, with electrically active concentrations approaching 1020 cm-3 is reported. The growth method is atmospheric chemical vapor deposition using germane and phosphine with N2 as carrier gas. Best results have been achieved using a relatively low growth temperature of 350ºC and a low PH3/GeH4 flow ratio, enabling a high concentration of P to be incorporated substitutionally. No P clusters are visible in high-angle annular dark-field STEM images. The results show excellent crystalline quality and acceptable surface uniformity, achieved with growth rates in the range of 5-10 nm / min. There is evidence that further improvements in active concentrations may be achievable by a further reduction in growth temperature and optimization of the gas flow conditions. The process holds promise for future n+junction fabrication in germanium.