Photoluminescence Evolution with Deposition Thickness of Ge Nanostructures Embedded in GaSb

Abstract

Germanium (Ge) possesses the intriguing properties of the tunability of indirect to direct bandgap by tensile strain and hence the enhancement of optical and electronic performances, which makes tensile-strained Ge very promising for optoelectronic integrated light sources. [1][2][3][4] Theoretically, a minimum 2% biaxial tensile strain is necessary for the indirect-to-direct bandgap conversion, [3,5] which is, unfortunately, much higher than that induced by the typical Ge-Si thermal mismatch of %0.25%. [6,7] While as an alternative high n-type doping was executed to push ahead with the directgap electronic transition by filling the indirect conduction band states, [8] the threshold was inevitably increased and the luminescent performance degraded, [9] and therefore that how to introduce higher tensile strain to Ge become a hot topic.A micromachine was designed to perform a tensile strain of about 2.7% on a Ge nanomembrane, well beyond the critical stain, to demonstrate the concept of the tensile-strain-induced light emission enhancement at room temperature. [10,11] Ge nanostructures embedded in latticemismatch III-V group matrix were another strategy introduced to realize highly tensile-strained Ge. [1,4,12,13] For example, a tensile strain of about 5% is reached in the self-assembled Ge/InAlAs quantum dots grown on InP substrate. [14,15] Different from the growth of Ge on InP and/or InAs that follows the the Volmer-Weber mode without Ge wetting layer, Ge embedded in antimonide obeys the Stranski-Krastanov growth mode and a clear tensile-strained 2D nanolayer exists. [15,16] As a result and owing to not only the large lattice mismatch of about 7.7% but also the presence of tensile-strained Ge nanolayer, GaSb is a preferred candidate as the matrix of highly