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

Hameed Naseem

Third Committee Member

Simon Ang

Keywords

Germanium Tin, Infrared Photodetector

Abstract

The demand of light-weight and inexpensive imaging system working in the infrared range keeps increasing for the last decade, especially for civil applications. Although several group IV materials such as silicon and germanium are used to realize detectors in the visible and near infrared region, they are not the efficient approach for imaging system in the short-wave infrared detection range and beyond due to bandgap limit. On the other hand, this market is heavily relied upon mature technology from III-V and II-VI elements over years, which are costly to growth and incompatible with available Si complementary metal-oxide-semiconductor (CMOS) foundries. This limits the fabrication of large scale focal plan arrays detectors in this detection range. Therefore, a material system that meets the necessary requirements has long been in demand.

The Ge1-xSnx material system has been introduced as a potential solution for low-cost high-performance photodetector for short-wave infrared towards mid-infrared detections due to its compatibility with Si CMOS process and wide detection range by incorporating more Sn in the alloy. Since then, immense growth efforts have been made to improve the material quality reaching device-quality using commercial chemical vapor deposition (CVD) reactors or molecular beam epitaxy (MBE) chambers.

This dissertation will develop Si-based GeSn photodetectors technology to realize low-cost high-performance focal plane arrays detectors working in the SWIR towards MIR. It began with the development of fabrication process of single element GeSn photoconductor and photodiode, followed by systematic characterization and analysis of detectors’ figures of merits to provide a more optimized structure. A peak responsivity of 20 A/W (photoconductor) and 0.34 A/W (photodiode) at 2 µm were achieved. An external quantum efficiency of 20 % was reported for the first time. The highest value of specific detectivity D* is only 3-4 times less than commercially available Extended-InGaAs detector. Surface passivation technique was also pursued to reduce surface leakage current. Finally, infrared imaging capability was demonstrated using single pixel detector. The study involves a wide range of Sn composition from 10 to 22 %.

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