| Metadata | Details |
|---|
| Publication Date | 2024-06-05 |
| Journal | ACS Omega |
| Authors | Lixia Wang, Shengming Xu, Jiangang Yang, Hui Huang, Zhe Huo |
| Institutions | Wuhan University, Beihang University |
| Citations | 33 |
| Analysis | Full AI Review Included |
- Core Value Proposition: Ultrawide Bandgap (UWBG) semiconductors (Ga2O3, Diamond, AlGaN/AlN) with bandgaps greater than 4.4 eV enable intrinsic solar-blind ultraviolet (DUV, < 280 nm) photodetection, eliminating the need for costly and limiting optical filters.
- Performance Highlights: UWBG SBPDs demonstrate exceptional performance, including record-high photoresponsivity (R up to 109 A W-1 in AlGaN phototransistors) and ultra-fast response speeds (down to nanoseconds in diamond devices).
- Ga2O3 Dominance: Beta-Ga2O3 is the most extensively studied platform, benefiting from the availability of large-area, high-quality single-crystal substrates, leading to high-performance MSM and Schottky photodiodes.
- Key Bottlenecks (Doping): A major challenge is achieving effective bipolar doping: p-type doping remains elusive for Ga2O3, and n-type doping is difficult for diamond, hindering the fabrication of high-quality p-n homojunctions.
- Key Bottlenecks (Substrates): Commercialization of diamond and AlGaN/AlN devices is limited by the lack of large-area, high-quality single-crystal substrates, leading to high defect densities and lattice mismatch issues.
- Future Direction: Research must focus on developing reliable bipolar doping strategies, scaling up high-quality substrate production, and integrating novel concepts like localized surface plasmon (LSP) effects and photogating to enhance device functionality.
| Parameter | Value | Unit | Context |
|---|
| Ga2O3 Bandgap (β-phase) | 4.8 | eV | Corresponds to solar-blind cutoff ~260 nm |
| Diamond Bandgap | 5.5 | eV | Corresponds to solar-blind cutoff ~225 nm |
| AlN Bandgap | 6.2 | eV | Corresponds to solar-blind cutoff ~200 nm |
| Ga2O3 Photoconductor R (Peak) | 259 | A W-1 | High EQE (7.9 x 104 %) achieved via avalanche multiplication at 20 V bias |
| Ga2O3 MSM D* (Record) | 7.4 x 1015 | Jones | Fully transparent device with embedded ITO electrodes |
| Ga2O3 Schottky R (Peak) | 9780.23 | A W-1 | Lateral device operating in avalanche mode at 60 V reverse bias |
| Ga2O3 Schottky Response Time | <5 | ¾s | Self-powered operational mode (Au/β-Ga2O3) |
| Diamond Photoconductor R | 22.6 | A W-1 | Single crystal pixel device, 50 V bias, 222 nm |
| Diamond Photoconductor Ďrise | 13 | ns | Single crystal pixel device, 50 V bias |
| Diamond MSM D* (Record) | 3.42 x 1015 | Jones | Hydrogen-plasma treated surface, 220 nm |
| AlGaN Phototransistor R (Record) | 2.9 x 109 | A W-1 | Quasi-pseudomorphic heterostructure, 213 nm |
| AlGaN Phototransistor D* (Record) | 4.5 x 1021 | Jones | Quasi-pseudomorphic heterostructure, 213 nm |
| AlGaN p-i-n EQE (Peak) | ~80 | % | Back-illuminated device, 275 nm, zero bias |
| AlGaN Dark Current (MSM) | <1 | pA | AlN spacer layer inserted, 5 V bias |
- Ga2O3 Crystal Growth and Film Deposition:
- Bulk crystals are grown using Edge-Defined Film-fed Growth (EFG), Czochralski (CZ), Float Zone (FZ), and Bridgman methods.
- Thin films and nanostructures are synthesized via Sputtering, Hydride Vapor Phase Epitaxy (HVPE), Metal-Organic Chemical Vapor Deposition (MOCVD), Molecular Beam Epitaxy (MBE), Pulsed Laser Deposition (PLD), and Atomic Layer Deposition (ALD).
- Ga2O3 Defect Management:
- Postannealing under an oxygen atmosphere is used to decrease intrinsic oxygen vacancies (VO), suppressing dark current and enhancing the photo-to-dark current ratio (PDCR).
- Element doping (e.g., Zn or Sn) is employed to mitigate VO defects and enhance conductivity.
- Diamond Film Growth and Contact Engineering:
- Bulk crystals are grown via High-Pressure-High-Temperature (HPHT) methods.
- Thin films are deposited using Chemical Vapor Deposition (CVD).
- Ohmic contacts are achieved using laser-induced graphitization or specific metal stacks (e.g., Ti/Au, Ti/WC) due to large Schottky barriers.
- Hydrogen plasma surface treatment is used to modulate the Schottky barrier height and surface defect states.
- AlGaN/AlN Epitaxy:
- Films are synthesized using MOCVD, MBE, Sputtering, and PLD.
- AlN/GaN period superlattices or AlN spacer layers are introduced to reduce the density of inversion domains (IDs) and suppress dark current.
- Device Architecture Optimization:
- MSM/Photoconductors: Interdigitated electrodes are used to maximize photosensitive area and minimize carrier transit distance.
- Schottky Diodes: Asymmetric metal contacts (Schottky/Ohmic) are used, often incorporating transparent electrodes (ITO, IZO) or 2D materials (graphene) to improve efficiency.
- p-i-n Junctions: An intrinsic (i-type) layer is incorporated to broaden the space charge region (SCR), optimizing quantum efficiency and response speed.
- Environmental Monitoring: Ozone hole monitoring and DUV radiation detection for public safety (e.g., smart glasses, wearable UV sensors).
- Industrial Safety: Flame detection, arc detection, and monitoring of high-temperature industrial processes where traditional Si-based detectors fail.
- Military and Aerospace: Missile tracking, surveillance, reconnaissance, and target acquisition, leveraging the ability of UWBG SBPDs to operate in harsh, high-temperature environments.
- High-Speed Communications: Wireless communications and high-speed optoelectronics, utilizing the fast response times (nanosecond to microsecond range) of diamond and AlGaN devices.
- Chemical and Biological Analysis: Specialized DUV light detection for analytical instruments.
- Next-Generation Electronics: Integration into fully transparent or semi-transparent electronic and optoelectronic devices (e.g., transparent displays, batteries, and automotive safety systems).
- Imaging Technology: Development of solar-blind imaging systems and Focal Plane Arrays (FPAs) by integrating pixel devices.
View Original Abstract
Ultrawide bandgap (UWBG) semiconductors, including Ga<sub>2</sub>O<sub>3</sub>, diamond, Al <sub><i>x</i></sub> Ga<sub>1-<i>x</i></sub> N/AlN, featuring bandgaps greater than 4.4 eV, hold significant promise for solar-blind ultraviolet photodetection, with applications spanning in environmental monitoring, chemical/biological analysis, industrial processes, and military technologies. Over recent decades, substantial strides in synthesizing high-quality UWBG semiconductors have facilitated the development of diverse high-performance solar-blind photodetectors (SBPDs). This review comprehensively examines recent advancements in UWBG semiconductor-based SBPDs across various device architectures, encompassing photoconductors, metal-semiconductor-metal photodetectors, Schottky photodiodes, p-n (p-i-n) photodiodes, phototransistors, etc., with a systematic introduction and discussion of their operational principles. The current state of device performance for SBPDs employing these UWBG semiconductors is evaluated across different device configurations. Finally, this review outlines key challenges to be addressed, aiming to steer future research endeavors in this critical domain.