Electrical and Computer Engineering ETDs

Publication Date

Summer 7-27-2019

Abstract

In this thesis, I present a reliable and efficient approach to heterogeneous integration of single-crystalline GaSb semiconductors with highly mismatched materials. The mismatch may refer to the crystalline structure and the thermal expansion coefficient of single-crystalline GaSb and the other materials of interest. The strategy of hetero-integration relies on epitaxial lift-off. This approach prevents the formation of extended structural defects that are detrimental to the performance of optoelectronic devices and preserves GaSb growth substrates for potential reuse.

Within my research work, I have overcome some outstanding challenges of epitaxial lift-off of GaSb, and I have demonstrated the operation of single-crystalline GaSb photovoltaic devices with unique architecture on single-crystalline Si substrates.

Using the pixelated approach for epitaxial lift-off, I release GaSb epilayers from GaSb substrates with 100% yield. By leveraging release and transfer of GaSb membranes on Si, I have demonstrated the operation of thin-film photovoltaic devices with areas of ~100sx100s um2 (i.e., pixelated solar cells). The photo-conversion efficiency of ~340x340 um2 pixelated devices amounts to ~2.6%, i.e., a comparable efficiency to what I extracted for a ~5 x 5 mm2 homo-epitaxial GaSb cell on a GaSb substrate.

I have performed a detailed structure-property relationships study to justify device characteristics in pixelated GaSb solar cells on Si. Specifically, I have determined the origin of non-ideal effects and leakage mechanisms underlying the device behaviour with and without illumination. These effects relate to the chemical and physical structure of surfaces and interfaces in small-area GaSb solar cells transferred to Si. These investigations are crucial to gain understanding and predictive control of performance in devices with unprecedented architecture.

In conclusion, I have established a reliable and efficient process to isolate GaSb epilayers without the formation of any extended defects. I have demonstrated thin films and pixelated GaSb photovoltaic devices on single-crystalline Si substrates, and I have performed a detailed structure-property relationship of the novel solar cells architectures.

My work will potentially impact a variety of optoelectronic devices that would benefit from the integration of III-Sb device layers with mismatched materials. These devices include high power infrared lasers, thermophotovoltaic cells, infrared detectors, and photovoltaic cells.

Keywords

Photovoltaics, GaSb membranes, Thin-films, Pixelation

Sponsors

NSF, DOE

Document Type

Dissertation

Language

English

Degree Name

Electrical Engineering

Level of Degree

Doctoral

Department Name

Electrical and Computer Engineering

First Committee Member (Chair)

Dr. Francesca Cavallo

Second Committee Member

Dr. Ganesh Balakrishnan

Third Committee Member

Dr. Payman Zarkesh-Ha

Fourth Committee Member

Dr. Nathan Jackson

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