Efficient above-band-gap light emission in germanium

Abstract

We report an above-band-gap radiative transition in the photoluminescence spectra of single crystalline Ge in the temperature range of 20~296 K. The temperature-independence of the peak position at ~0.74 eV is remarkably different from the behavior of direct and indirect gap transitions in Ge. This transition is observed in n-type, p-type, and intrinsic single crystal Ge alike, and its intensity decreases with the increase of temperature with a small activation energy of 56 meV. Some aspects of the transition are analogous to III-V semiconductors with dilute nitrogen doping, which suggests that the origin could be related to an isoelectronic defect.