In recent years, Ga2O3 solar-blind photodetectors (SBPDs) have received great attention for their potential applications in solar-blind imaging, deep space exploration, confidential space communication, etc. In this work, we demonstrated an ultra-high-performance ε-Ga2O3 metal–semiconductor–metal (MSM) SBPD. The fabricated photodetectors exhibited a record-high responsivity and fast decay time of 230 A/W and 24 ms, respectively, compared with MSM-structured Ga2O3 photodetectors reported to date. Additionally, the ε-Ga2O3 MSM SBPD presents an ultrahigh detectivity of 1.2 × 1015 Jones with a low dark current of 23.5 pA under an operation voltage of 6 V, suggesting its strong capability of detecting an ultraweak signal. The high sensitivity and wavelength selectivity of the photodetector were further confirmed by the record-high responsivity rejection ratio (R 250 nm/R 400 nm) of 1.2 × 105. From the temperature-dependent electrical characteristics in the dark, the thermionic field emission and Poole–Frenkel emission were found to be responsible for the current transport in the low and high electric field regimes, respectively. In addition, the gain mechanism was revealed by the Schottky barrier lowering effect due to the defect states at the interface of the metal contact and Ga2O3 or in the bulk of Ga2O3 based on current transport mechanism and density functional theory calculations. These results facilitate a better understanding of ε-Ga2O3 photoelectronic devices and provide possible guidance for promoting their performance in future solar-blind detection applications.

Light detection in the deep-ultraviolet (DUV) solar-blind waveband has attracted interest due to its critical applications, especially in safety and space detection. A DUV photodetector based on wide-bandgap semiconductors provides a subversive scheme to simplify the currently mature DUV detection system. As an ultra-wide-bandgap (4.4–5.3 eV) semiconductor directly corresponding to the DUV solar-blind waveband, Ga2O3 has an important strategic position in the prospective layout of semiconductor technology owing to its intrinsic characteristics of high breakdown electric field, excellent tolerance of high/low temperature, high resistance to radiation, and rich material systems. As the only native substrate that can be fabricated from melt-grown bulk single crystals, β-Ga2O3 has attracted a lot of attention both in power-electronic and photo-electronic devices. In addition, other metastable phases (e.g. α, ϵ, γ) of Ga2O3 have attracted great interest due to their unique properties. In this work, we discuss the advances in achieving bulk and film Ga2O3 materials with different crystal phases. In addition, the latest achievements with polymorphous Ga2O3-based solar-blind photodetectors (SBPDs) and the methods to enhance their performance, including doping, annealing, and transparent electrodes, are also discussed. Furthermore, as the most desirable application, DUV imaging technologies based on Ga2O3 SBPDs are systematically summarized. Finally, conclusions regarding recent advances in Ga2O3 SBPDs, remaining challenges, and prospects are presented and discussed.

Ga2O3‐based solar‐blind photodetectors (PDs) are now attracting more and more attention for their potential application in optical imaging, spatial communication, etc. However, the performance of ever‐reported Ga2O3‐based PDs is still not good enough, strongly affected by either the Ga2O3 crystalline quality or the device structure, which severely limits their capability to detect extremely weak signals and achieve future applications. In this work, solar‐blind field‐effect phototransistor based on radio‐frequency‐magnetron sputtered amorphous gallium oxide thin film with ultrahigh photodetection performance are demonstrated. The key feature of the device is gate‐tunable photodetection enabling ultrahigh responsivity of 4.1 × 103 A W−1, external quantum efficiency of 2 × 106%, and detectivity of 2.5 × 1013 Jones under a 70 µW cm−2 weak signal of 254 nm light due to a high internal gain and field effect control of the phototransistor. Furthermore, high‐resolution imaging is achieved for the imaging target by integrating the as‐fabricated photodetectors into the imaging system, which is the first report on solar‐blind imaging of amorphous gallium oxide photodetectors. Such field‐effect phototransistors with ultrahigh performance and excellent imaging capability address a significant step toward the feasibility and practicability of gallium oxide photodetectors in solar‐blind imaging system.

photodetector (SBPD), as an indispensable part of spectral detectors, plays important roles distinctively in various crucial applications, such as missile tracking, flame prewarning, secure communication, and environment monitoring. [1][2][3][4] In terms of the possible harsh application environment, high-performance SBPDs with excellent tolerance towards high temperature, high voltage, and high radiation, are required inevitably. Based on low cost and mature technology, the currently available Si-based SBPDs are facing the challenges of filter dependence, low penetration depth of high-energy ultraviolet (UV) photons, and finite responsivity (R) towards solar-blind region. [5][6][7] Especially, Si-based SBPDs suffer serious thermal instability owing to the narrow bandgap, which suppresses their high-temperature applications. Advanced SBPDs based on wide bandgap (WBG) materials, such as MgZnO, [8] AlGaN, [9,10] diamond, [11] and Ga 2 O 3 , [12] are believed as subversive substitutes of Si-based SBPDs. Among the various WBG materials, Ga 2 O 3 is the most desirable candidate for SBPDs applications based on the facts that, i) its ultra-wide bandgap (4.5-4.9 eV) corresponds to the solar-blind region directly without the necessity of bandgap modulation by doping or alloying process; [13] ii) its high absorption coefficient for high-energy UV photons benefits outstanding sensitivity in solar-blind region; [14] iii) it balances high solar-bind response and material workability; [15] iv) its large-size bulk single crystals can be put into mass production by low-cost melt-grown methods; [16] and most importantly, v) it has high structural stability toward temperature, radiation, and electric field for harsh-environment application. [17] High-quality Ga 2 O 3 material, including single-crystal substrates, nanostructures, and epitaxial films, [14,18,19] facilitate sharp junction interface, such as P-N heterojunction, [20] N-N heterojunction, [21] phase junction, [22] and Schottky junction, [23] to improve the solar-blind response performance. Nevertheless, so far, high-performance SBPDs based on high-quality Ga 2 O 3 Gallium oxide (Ga 2 O 3 ), with an ultrawide bandgap, is currently regarded as one of the most promising materials for solar-blind photodetectors (SBPDs), which are greatly demanded in harsh environment, such as space exploration and flame prewarning. However, realization of high-performance SBPDs with high tolerance toward harsh environments based on low-cost Ga 2 O 3 material faces great challenges. Here, defect and doping (DD) engineering towards amorphous GaO X (a-GaO X ) has been proposed to obtain ultrasensitive SBPDs for harsh condition application. Serious oxygen deficiency and doping compensation of the engineered a-GaO X film ensure the high response currents and low dark currents, respectively. Annealing item in nitrogen of DD engineering also incurs the recrystallization of material, formation of nanopores by oxygen escape, and suppression of sub-bandgap defect states. As a result, the tailored GaO...

Ultraviolet (UV) photodetectors (PDs) have drawn great attention in recent years due to their potential application in civil and military fields. Because of its ultrawide bandgap, low cost, strong radiation hardness, and high thermal and chemical stability with high visible-light transparency, Ga 2 O 3 is regarded as the most promising candidate for UV detection. Furthermore, the bandgap of Ga 2 O 3 is as high as 4.7-4.9 eV, directly corresponding to the solar-blind UV detection band with wavelength less than 280 nm. There is no need of doping in Ga 2 O 3 to tune its bandgap, compared to AlGaN, MgZnO, etc, thereby avoiding alloy composition fluctuations and phase separation. At present, solar-blind Ga 2 O 3 photodetectors based on single crystal or amorphous Ga 2 O 3 are mainly focused on metal-semiconductor-metal and Schottky photodiodes. In this work, the recent achievements of Ga 2 O 3 photodetectors are systematically reviewed. The characteristics and performances of different photodetector structures based on single crystal Ga 2 O 3 and amorphous Ga 2 O 3 thin film are analyzed and compared. Finally, the prospects of Ga 2 O 3 UV photodetectors are forecast.