Date of Graduation

5-2025

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Engineering (PhD)

Degree Level

Graduate

Department

Electrical Engineering and Computer Science

Advisor/Mentor

Du, Wei

Committee Member

Yu, Shui-Qing (Fisher)

Second Committee Member

Zhong, Chen

Third Committee Member

El-Ghazaly, Samir

Keywords

Avalanche Photodiodes; Germanium-Tin; Infrared; Ion Implantation; Lasers; Photodetector

Abstract

Short-wave infrared (SWIR) and mid-wave infrared (MWIR) photodetectors have attracted increasing attention for the past few decades. SWIR and MWIR detectors are used for a wide range of applications in military and civilian defense, such as future automotive night vision, video surveillance security cameras, and integrated night vision in mobile/wearable electronics. The current market-dominating IR photodetector technology is mainly developed with the costly III-V or II-V material systems, such as InGaAs, InSb, and HgCdTe. While many efforts have been made towards the hybrid integration of III-Vs or II-VIs on a Si substrate, it is highly desirable to develop an alternative material featuring lower-cost and high-performance for photodetectors covering broad IR wavelength range.

Recent study of all-group-IV alloy SiGeSn opens a new venue for Si-based optoelectronics. SiGeSn offers: (1) The ability to independently engineer the lattice constant and bandgap by appropriately selecting the compositions of Si, Ge, and Sn; (2) The ability to achieve true direct bandgap material by incorporating a few percent Sn; (3) The possibility of forming desirable type-I band alignment to provide a favorable quantum confinement for the design of optoelectronics; (4) The IR wavelength coverage up to 12 μm through band-to-band transitions and all wavelengths beyond 12 μm through intersubband transitions; (5) The compatibility with CMOS processes with a low growth temperature (below 400 oC). The key enabling factors for SiGeSn over all current IR technologies also include significantly lower radiative and Auger recombination (10-28~10-29 cm6 /s) coefficients for longer carrier lifetime (>100 μs), and larger oscillator strength for higher absorption coefficient (>104/cm), giving a shorter carrier extraction time, lower dark current, and higher internal quantum efficiency. My dissertation shows the development of general GeSn device fabrication processes, which were later employed in the fabrication of GeSn laser and detector devices. This successfully demonstrated the first electrically injected GeSn laser and avalanche photodiode, which showed clear punch-through and avalanche breakdown behavior.

Further, investigations into Ion implantation of arsenic (n-type) and boron (p-type) in GeSn (~10% Sn) is feasible but induces lattice damage. Higher doses and energies cause crystal disorder up to amorphization, partially healed by low-temperature rapid thermal annealing. Annealing at 300°C recovers some damage, while 400°C significantly restores crystallinity for Sn ≤11%. SIMS confirms impurity incorporation, and post-implant annealing activates p–n junctions. A fabricated GeSn diode with implanted regions exhibits rectifying I–V behavior and infrared photo response.

This work advances monolithic GeSn-based avalanche photodiodes (APDs) on silicon, enabling extended infrared detection and CMOS compatibility. A SACM structure with a GeSn absorber, Si multiplication layer, and Ge buffer enhances carrier transport, achieving a broad spectral response beyond 2.1 μm at room temperature. The GeSn-on-Si APDs show clear punch-through and avalanche breakdown. Internal gain is evident, with multiplication factors of ~1.4 at 250 K and ~4–4.5 at 77 K.

These findings highlight GeSn's potential for extending silicon photonics into the infrared. GeSn APDs on Si achieve spectral response beyond Si and Ge bandgaps, with avalanche gain in the 1.5–2.0 μm range. CMOS-compatible ion implantation and low-temperature annealing enable GeSn integration into standard silicon processes, paving the way for monolithic, CMOS-compatible infrared photodetectors and optoelectronic devices in the SWIR/MWIR regimes.

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