Enhanced electroluminescence from a free-standing tensilely strained germanium nanomembrane light-emitting diode**Project supported by the Fundamental Research Funds for the Central University of China (No. 7214428001).

Abstract

Ge has become a promising material for Si-based optoelectronic integrated circuits (OEIC) due to its pseudo-direct bandgap. In this paper we achieved tensilely strained Ge free-standing nanomembrane (NM) light-emitting diode (LED), using silicon nitride thin film with high stress. The tensile stress in the Ge layer can be controlled by adjustable process parameters. An expected redshift of electroluminescence (EL) in Ge NM LED is observed at room temperature, which has been attributed to the shrinking of its direct bandgap relative to its indirect bandgap. An EL with dramatically increased intensity was observed around 1876 nm at a tensile strain of 1.92%, which demonstrates the direct-band recombination in tensilely strained Ge NM.