Cao, Zhongming
(2021)
Novel Semiconductor Materials for Mid-Infrared Optoelectronic Application.
Doctor of Philosophy thesis, University of Liverpool.
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Abstract
Thin film gallium antimony bismuth (GaSbBi) grown on GaSb substrate via molecular beam epitaxy (MBE) have been explored in this thesis by characterising the films electrical, physical and optical properties. From these wafers Schottky diodes, and metal-semiconductor-metal photodetectors (MSM-PDs) have been investigated. Another promising material for infrared photodetectors is InAs, in this work the use of high-k based dielectrics has been investigated to improve the passivation of InAs avalanche photodiodes (APDs). Initially, the influence of postgrowth thermal annealing on GaSbBi Schottky barrier diodes has been investigated. The I-V characteristics indicated a better ideality factor and less leakage current at the reverse bias, as the annealing temperature increased up to 500 °C for a duration of 30 min. X-ray diffraction and scanning transmission electron microscope measurements were performed to verify that the bismuth composition was unaffected during the annealing process. Energy dispersive x-ray analysis indicated that Sb clustering occurs at high annealing temperatures, resulting in a concomitant degradation in the electrical performance. The optimum electrical characteristics of the diode were obtained with an annealing temperature of 500 °C for 30 min, resulting in an ideality factor of 1.3 being achieved. The optimised GaSbBi and GaSbN samples were then fabricated into MSM-PDs and verify the viability of using GaSbBi and GaSbN as active layers in photodetector. The cut-off wavelength extended to 1950 nm (2.9% Bi), 1990 nm (3.8% Bi), 2080 nm (4.5% Bi) and 2190 nm (1.5% N) have been observed, demonstrating the viability of using Bi and N for mid-infrared sensing. The comparison of different geometry on the photo spectral response indicating Bi incorporation increase the lattice expansion, which reduce the carrier concentration of the devices. Optimization of InAs based APDs are reported in this thesis. The use of high-k dielectric material as a passivation layer to improve the performance of InAs APDs are discussed. Three potential passivation layers, including ZnO, Al2O3 and MgO have been identified, all of which enables the suppression of surface leakage in smaller sized InAs APDs with a radius of 50 ìm and at lower temperatures of 175 K compared to a reference SU8 device. The influence of repeated temperature cycling on these layers has also been investigated with ZnO observed clear degradation after ten cycle, MgO shows almost a 10% higher current at a constant voltage after ten temperature cycles and Al2O3 passivated device, exhibiting no change in performance after temperature cycles. Suggesting Al2O3 as an effective and stable material for InAs APDs.
| Item Type: | Thesis (Doctor of Philosophy) |
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| Divisions: | Faculty of Science and Engineering > School of Electrical Engineering, Electronics and Computer Science |
| Depositing User: | Symplectic Admin |
| Date Deposited: | 20 Oct 2021 14:23 |
| Last Modified: | 18 Jan 2023 21:30 |
| DOI: | 10.17638/03135648 |
| Supervisors: |
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| URI: | https://livrepository.liverpool.ac.uk/id/eprint/3135648 |
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