A review of Ga₂O₃ deep-ultraviolet metal–semiconductor Schottky photodiodes

Abstract

Deep-ultraviolet (DUV) photodetectors are fundamental building blocks in lots of solid-state DUV optoelectronics, whose prosperity is pinned hope on continuous innovations on semiconductor materials and physics of device structures. Conquering the technological obstacles in narrow bandgap silicon-based optoelectronics (photodetectors and photonics), wide bandgap semiconductor gained a high level of enthusiasm in constructing DUV photodetector, thereinto Ga2O3 is a typical representative benefiting from its promising physical and chemical properties in nature, especially for its energy bandgap around 4.5-5.2 eV for its five phases (α, β, γ, ε and δ). Which just right provides a hard-won opportunity to respond to DUV light irradiation without the need for adjusting the component in compounds and/or adding external optical instruments, as some compound semiconductors AlxGa1-xN, MgxZn1-xO, etc. According to literature reports on Ga2O3-based photodetectors, the device morphology includes metal-semiconductor-metal (MSM) photodetector, homojunction or heterojunction photodetector, phototransistor, and Schottky photodiode. What calls for special attention is that Schottky photodiode with a rectified Schottky junction has certain advantages: easy fabrication, fast photoresponse, less high-temperature diffusion, low dark current, high detectivity, and self-powered operation; in spite of weaknesses of thin depletion layer and low barrier at metal-semiconductor (M-S) interface. Therefore, in this concise literature review article, the recent progresses on Ga2O3-based Schottky photodiodes is discussed in order to show some suggestions on choice of Schottky metal, interfacial barrier modulation, space electric field adjustment, energy band engineering, and photodetection performance improvement, for promoting the further developments of DUV photodetection in the near future.

Comprehensive Study on Ultra-Wide Band Gap La2O3/ε-Ga2O3 p–n Heterojunction Self-Powered Deep-UV Photodiodes for Flame Sensing

“…Solar-blind region corresponds to ultraviolet (UV) light at a wavelength of 200–280 nm, which can be absorbed by ozone in the atmosphere. In recent years, solar-blind photodetectors (SBPDs) have raised increasing attention from researchers for being able to work without the influence of solar radiation. − Benefiting from that, SBPDs have been widely used in many civil and military areas, with fire detection and imaging being two major applications. − Among the most popular structures of SBPDs, the p–n junction has demonstrated high performance including low dark current ( I dark ), high photocurrent ( I photo ), high sensitivity, and fast response speed. Most importantly, at the interface of p–n junction there exists a built-in electric field ( E built‑in ) owing to the formation of the space charge region, facilitating the separation of electron–hole pairs, thus allowing the device to be self-powered without external biases, which meets the requirements of today’s environmentally friendly society. − …”

An enhanced ultrasensitive solar-blind UV photodetector based on an asymmetric Schottky junction designed with graphene/β-Ga2O3/Ag

“…Additionally, asymmetric Schottky barrier structures can achieve a reduced dark current, higher responsivity and faster response time than MSM symmetric barrier structures. 17–19 By constructing an asymmetric Schottky junction structure, Qin et al fabricated the Au/Ti/Pt/ε-Ga 2 O 3 /Ti/Au detector, achieving a low dark current of 25 pA, an ultrahigh responsivity of 84 A W −1 and a fast response speed of 100 ms. 20…”

“…Additionally, asymmetric Schottky barrier structures can achieve a reduced dark current, higher responsivity and faster response time than MSM symmetric barrier structures. [17][18][19] By constructing an asymmetric Schottky junction structure, Qin et al fabricated the Au/Ti/Pt/ e-Ga 2 O 3 /Ti/Au detector, achieving a low dark current of 25 pA, an ultrahigh responsivity of 84 A W À1 and a fast response speed of 100 ms. 20 Owing to its ultra-high electrical conductance and mobility, as well as high transmittance for light in the deep ultraviolet to infrared spectral range, [21][22][23] graphene is often used as a transparent conductive electrode. And a significant number of studies have already succeeded in using graphene as an electrode in Ga 2 O 3 -based devices that form Schottky contacts: the graphene/ b-Ga 2 O 3 wafer Schottky junction photodetector had a responsivity of 39.3 A W À1 , the p-GaN/b-Ga 2 O 3 /graphene photodetector operated with a responsivity up to 12.8 A W À1 , the b-Ga 2 O 3 MSM solar blind photodetectors with graphene electrodes exhibits high responsivity of 29.8 A W À1 , and the photodetector with a graphene/b-Ga 2 O 3 /graphene hybrid structure had a responsivity of 9.66 A W À1 .…”

Photogain-Enhanced Signal-to-Noise Performance of a Polycrystalline Sn:Ga2O3 UV Detector via Impurity-Level Transition and Multiple Carrier Transport

“…2 The ultrawide E g of Ga 2 O 3 makes it highly suitable for fabricating solar-blind ultraviolet photodetectors, which operate in the solar-blind ultraviolet waveband (200−280 nm, also known as UV−C). 3 These photodetectors vary according to their structures, including metal−semiconductor−metals (MSMs), 4 heterojunctions, 5 Schottky barrier diodes (SBDs), 6 and others. 7 Besides, they can work as a single device or together as an array.…”

“…Gallium oxide (Ga 2 O 3 ), a popular material for the new generation of power electronics and optoelectronic devices, exhibits a wide band gap ( E g ) of ∼4.8 eV, a high critical electric field ( E C ), and variable doping concentrations ranging from 10 14 to 10 20 cm –3 , which meet the needs for high-power devices and integrated systems . The ultrawide E g of Ga 2 O 3 makes it highly suitable for fabricating solar-blind ultraviolet photodetectors, which operate in the solar-blind ultraviolet waveband (200–280 nm, also known as UV–C) . These photodetectors vary according to their structures, including metal–semiconductor–metals (MSMs), heterojunctions, Schottky barrier diodes (SBDs), and others .…”