Theoretical Analysis of GeSn Alloys as a Gain Medium for a Si-Compatible Laser

• Published in: IEEE journal of selected topics in quantum electronics Vol. 19; no. 5; p. 1502706
• Main Authors: Dutt, B., Hai Lin, Sukhdeo, D. S., Vulovic, B. M., Gupta, S., Donguk Nam, Saraswat, K. C., Harris, J. S.
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.09.2013; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Alloys; Conduction band; Density; Diode lasers; Doping; Gain; Germanium; GeSn alloy; infrared lasers; Lasers; optoelectronic materials; Photonic band gap; Photonics; semiconductor lasers; semiconductor materials; Silicon; theory and design; Threshold current; Tin
• ISSN: 1077-260X; 1558-4542
• DOI: 10.1109/JSTQE.2013.2241397

In this paper, a theoretical analysis of unstrained GeSn alloys as a laser gain medium was performed. Using the empirical pseudopotential method, the band structure of GeSn alloys was simulated and verified against experimental data. This model shows that GeSn becomes direct bandgap with 6.55% Sn concentration. The optical gain of GeSn alloys with 0-10% Sn concentration was calculated with different n-type doping concentrations and injection levels. It is shown theoretically that adding Sn greatly increases the differential gain owing to the reduction of energy between the direct and indirect conduction bands. For a double-heterostructure laser, the model shows that at a cavity loss of 50 cm -1 , the minimum threshold current density drops 60 times from Ge to Ge 0.9 Sn 0.1 , and the corresponding optimum n-doping concentration of the active layer drops by almost two orders of magnitude. These results indicate that GeSn alloys are good candidates for a Si-compatible laser.