Temperature (T)-dependent photoluminescence (PL) has been investigated for both p-Ge and n-Ge1-ySny films grown on Si substrates. For the p-Ge, strong direct bandgap (ED) along with weak indirect bandgap related (EID) PL at low temperatures (LTs) and strong ED PL at room temperature (RT) were observed. In contrast, for the n-Ge1-ySny, very strong dominant EID PL at LT and strong ED PL were observed at RT. This T-dependent PL study indicates that the indirect-to-direct bandgap transitions of Ge1-ySny might take place at much lower Sn contents than the theory predicts, suggesting that these Ge1-ySny could become very promising direct bandgap semiconductors.
Applied Physics Letters
Mee-Yi Ryu, Tom R. Harris, Y. K. Yeo, R. T. Beeler, J. Kouvetakis; Temperature-dependent photoluminescence of Ge/Si and Ge1-ySny/Si, indicating possible indirect-to-direct bandgap transition at lower Sn content. Appl. Phys. Lett. 29 April 2013; 102 (17): 171908. https://doi.org/10.1063/1.4803927