Impact of tensile strain on low Sn content GeSn lasing

Denis Rainko,Zoran Ikonic,Daniela Stange,Dan Buca,Detlev Grützmacher,Etienne Herth,Nils von den Driesch,Anas Elbaz,Philippe Boucaud,Moustafa El Kurdi

doi:10.1038/s41598-018-36837-8

Abstract

In recent years much effort has been made to increase the Sn content in GeSn alloys in order to increase direct bandgap charge carrier recombination and, therefore, to reach room temperature lasing. While being successful for the former, the increase of Sn content is detrimental, leading to increased defect concentrations and a lower thermal budget regarding processing. In this work we demonstrate strong photoluminescence enhancement in low Sn content Ge0.94Sn0.06 layers by implementing tensile strain. Fitting of the calculated photoluminescence spectra to reproduce our experimental results indicates a strain of ~1.45%, induced via an SiNx stressor layer, which is strong enough to transform the investigated layer into a direct bandgap semiconductor. Moreover, theoretical calculations, using the 8-band k·p model, show the advantages of using low Sn content tensile strained GeSn layers in respect to gain and lasing temperature. We show that low Sn content GeSn alloys have a strong potential to enable efficient room temperature lasers on electronic-photonic integrated circuits.

Highlights

Si photonics is entering the market for short haul interconnects to construct energy efficient data centers and high performance computers
This work presents the possibilities of implementing tensile strain into low Sn content GeSn
Fitting PL measurements at 80 K we extract a tensile strain of ~1.45% corresponding to a directness of 94 meV for GeSn alloys with 6 at.% Sn

Summary

Introduction

Si photonics is entering the market for short haul interconnects to construct energy efficient data centers and high performance computers. Compressive strain on the other hand increases the requirements for Sn content in order to reach direct bandgap GeSn. introduced in the early 80 s’, the epitaxy of GeSn alloys has recently strongly advanced, due to the introduction of new precursors into chemical vapor deposition (CVD) processes[5,6]. Based on 8-band k∙p calculations, it has been shown that, in the case of CVD grown high Sn content GeSn/ SiGeSn heterostructures, efficient carrier confinement is limited by the low Si incorporation in the barrier[11]. Less attention has been paid so far to the possibilities of combining low Sn content alloys with tensile strain in order to reach direct bandgap GeSn15,16. For GeSn, first experiments show that tensile www.nature.com/scientificreports/

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