Advances in In Situ Boron and Phosphorous Doping of SiGeSn

Abstract

Dopant concentrations higher than 1 × 1019 cm−3 are required to improve the performances of various GeSn based devices such as photodetectors, electrically pumped lasers and so on. In this study, the in situ Boron and Phosphorous doping of SiGeSn was investigated, building upon recent studies on in situ B or P doped GeSn. The surfaces of intrinsic and lowly doped pseudomorphic SiGeSn layers were rough. By contrast, a 〈110〉 cross hatch was recovered and surfaces as smooth as the Ge Strain-Relaxed Buffers underneath were obtained for the highest B2H6 or PH3 mass-flows. The surface Root Mean Square roughness and Zrange values were then as low as 0.36 nm and 2.86 nm for SiGeSn:B, and 0.47 nm and 4.60 nm for SiGeSn:P. In addition, Si contents as high as 25% were obtained, notably in SiGeSn:B layers. Dopants were almost fully electrically active in those SiGeSn:B and SiGeSn:P layers, with carrier concentrations as high as 2.0 × 1020 cm−3 and 2.7 × 1020 cm−3, respectively. For SiGeSn:P, the shortcoming of in situ doped GeSn:P was overcome, that is the formation of electrically inactive SnmPnV clusters for high PH3 mass-flows. Such electrically active carrier concentrations will be beneficial for (Si)GeSn based devices, but also for all Group-IV based devices with extremely low thermal budget constraints.