Very Low Temperature Epitaxy of Heavily In Situ Phosphorous Doped Ge Layers and High Sn Content GeSn Layers

Abstract

We have studied in the 300–350°C temperature range, the 100 Torr epitaxy of heavily in-situ phosphorous doped Ge and high Sn content GeSn alloys in a 200 mm industrial Reduced Pressure - Chemical Vapor Deposition tool. We have first of all quantified the impact of the phosphine (PH3) flow on the structural and electrical properties of Ge:P layers. To that end, we have used a dedicated low temperature Ge precursor, digermane (Ge2H6), in order to promote P incorporation. We have reached very high atomic and electrically active P concentrations, at most 5 × 1020 cm−3 and 7.5 × 1019 cm−3, respectively. We have then evaluated the impact of the Ge2H6 and SnCl4 flows on the GeSn growth kinetics at 325°C, 100 Torr. As expected, the GeSn growth rate increases almost linearly with the Sn concentration, from 5 up to 21 nm.min−1. The Sn atoms seem to catalyze H desorption from the surface, resulting in higher GeSn growth rates, then. Finally, we have studied the impact of temperature, in the 300–350°C range, on the GeSn growth kinetics. The GeSn growth rate exponentially increases with the temperature, from 15 up to 32 nm.min−1. The associated activation energy is low, e.g. Ea = 11 kcal.mol−1. Really high Sn concentrations (at most 15%) were obtained in smooth, single crystalline layers.