Date of Graduation

8-2018

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Engineering (PhD)

Degree Level

Graduate

Department

Electrical Engineering

Advisor

Shui-Qing Yu

Committee Member

Gregory Salamo

Second Committee Member

Simon Ang

Third Committee Member

Hameed Naseem

Keywords

Chemical Vapor Deposition, GeSn Alloy, Mid Infrared Laser

Abstract

Si photonics is a rapidly expanding technology that integrates photonic circuits onto a Si substrate. The integration of Si electronics and photonics has been a successful technology for a wide range of applications. Group-IV alloy GeSn has drawn great attentions as a complementary metal–oxide–semiconductor compatible optoelectronic material for Si photonics. The devices based on GeSn alloy could be monolithically integrated into well-established and high-yield Si integrated circuits, which is favorable for chip-scale Si photonics featuring smaller size, lower cost, and higher reliability.

The relaxed GeSn with high material quality and high Sn composition is highly desirable to cover mid-infrared wavelength. A systematic study of GeSn strain relaxation mechanism and its effects on Sn incorporation during the epitaxy via chemical vapor deposition was conducted. It was discovered that Sn incorporation into Ge lattice sites is limited by high compressive strain rather than historically acknowledged chemical reaction dynamics, which was also confirmed by Gibbs free energy calculation. Following the discovered growth mechanism, a world-record Sn content of 22.3% was achieved. Even higher Sn content could be obtained if further continuous growth with the same recipe is conducted.

The GeSn laser with higher Sn content is highly desired to cover longer wavelength in mid-infrared. This work demonstrated optically pumped edge-emitting GeSn lasers under two different pumping lasers with 1064 and 1950 nm wavelengths. The device structure featured Sn compositional graded with the maximum Sn content of 22.3%. Under the 1950 nm pumping laser, the GeSn laser achieved the world-record near room temperature lasing (270 K). The corresponding lasing wavelength has been extended up to 3442 nm, an unprecedented GeSn lasing wavelength so far in the world.

The GeSn/GeSn/GeSn single and double quantum wells were also investigated to further improve laser performance. The unintentional Ge interlayer between barrier and well region of QW structure was removed by introducing the GeSn with variable Sn content as the buffer layer. As a result, the QW structure was demonstrated as the true type-I and direct bandgap structure, which is advantageous for the optoelectronic devices.

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