Single-Crystalline All-Oxide α-γ-β Heterostructures for Deep-Ultraviolet Photodetection

High-Performance Ga2O3 Solar-Blind Photodetector Based on Thermal Oxidized Ga Buffer-Layer

High-performance Ga2O3 solar-blind photodetectors are critical for applications due to their selective solar-blind ultraviolet sensitivity. The quality of the Ga2O3 film has a significant impact on the performance of photodetectors. This study presents an innovative approach to enhancing the quality of Ga2O3 films through the introduction of a naturally graded buffer layer, which is formed by the oxidation of a metallic Ga film and significantly improves interface stability by accommodating lattice mismatches and reducing defects. The structural and compositional characteristics of Ga2O3 films were comprehensively analyzed using UV-vis (ultraviolet-visible) spectroscopy, AFM (Atomic Force Microscope), PL (Photoluminescence Spectroscopy), TEM (Transmission Electron Microscope), and XPS (X-ray Photoelectron Spectroscopy). The photodetectors fabricated from these films demonstrate responsivity of 99.8 mA/W and a solar-blind UV/UV ratio of 1.17 × 103, with significant improvement compared to direct deposited films. This research highlights the potential of natural buffering layers to advance the performance of Ga2O3-based solar-blind UV detectors.

A High-Performance ε-Ga2O3-Based Deep-Ultraviolet Photodetector Array for Solar-Blind Imaging

One of the most important applications of photodetectors is as sensing units in imaging systems. In practical applications, a photodetector array with high uniformity and high performance is an indispensable part of the imaging system. Herein, a photodetector array (5 × 4) consisting of 20 photodetector units, in which the photosensitive layer involves preprocessing commercial ε-Ga₂O₃ films with high temperature annealing, have been constructed by low-cost magnetron sputtering and mask processes. The ε-Ga₂O₃ ultraviolet photodetector unit shows excellent responsivity and detectivity of 6.18 A/W and 5 × 10¹³ Jones, respectively, an ultra-high light-to-dark ratio of 1.45 × 10⁵, and a fast photoresponse speed (0.14/0.09 s). At the same time, the device also shows good solar-blind characteristics and stability. Based on this, we demonstrate an ε-Ga₂O₃-thin-film-based solar-blind ultraviolet detector array with high uniformity and high performance for solar-blind imaging in optoelectronic integration applications.

Ultrahigh Gain Solar Blind Avalanche Photodetector Using an Amorphous Ga2O3-Based Heterojunction

Solar blind photodetectors with a cutoff wavelength within the 200-280 nm region is attracting much attention due to their potential civilian and military applications. The avalanche photodetectors (APDs) formed based on wide-bandgap semiconductor Ga₂O₃ are expected to meet emerging technological demands. These devices, however, suffer from limitations associated with the quality of as-grown Ga₂O₃ or the difficulty in alleviating the defects and dislocations. Herein, high-performance APDs incorporating amorphous Ga₂O₃ (a-Ga₂O₃)/ITO heterojunction as the central element have been reliably fabricated at room temperature. The a-Ga₂O₃-based APDs exhibits an ultrahigh responsivity of 5.9 × 10⁴ A/W, specific detectivity of 1.8 × 10¹⁴ Jones, and an external quantum efficiency up to 2.9 × 10⁷% under 254 nm light irradiation at 40 V reverse bias. Notably, the gain could reach 6.8 × 10⁴, indicating the outstanding capability for ultraweak signals detection. The comprehensive superior capabilities of the a-Ga₂O₃-based APDs can be ascribed to the intrinsic carrier transport manners in a-Ga₂O₃ as well as the modified band alignment at the heterojunctions. The trade-off between low processing temperature and superior characteristics of a-Ga₂O₃ promises greater design freedom for realization of wide applications of emerging semiconductor Ga₂O₃ with even better performance since relieving the burden on the integration progress.

Comprehensively Improved Performance of β-Ga2O3 Solar-Blind Photodetector Enabled by a Homojunction with Unique Passivation Mechanisms

Ga₂O₃-based solar-blind photodetectors have been extensively investigated for a wide range of applications. However, to date, a lot of research has focused on optimizing the epitaxial technique or constructing a heterojunction, and studies concerning surface passivation, a key technique in electronic and optoelectronic devices, are severely lacking. Here, we report an ultrasensitive metal-semiconductor-metal photodetector employing a β-Ga₂O₃ homojunction structure realized by low-energy surface fluorine plasma treatment, in which an ultrathin fluorine-doped layer served for surface passivation. Without inserting/capping a foreign layer, this strategy utilized fluorine dopants to both passivate local oxygen vacancies and suppress surface chemisorption. The dual effects have opposite impacts on device current magnitude (by suppressing metal/semiconductor junction leakage and inhibiting surface-chemisorption-induced carrier consumption) but dominate in dark and under illumination, respectively. By means of such unique mechanisms, the simultaneous improvement on dark and photo current characteristics was achieved, leading to the sensitivity enhanced by nearly 1 order of magnitude. Accordingly, the 15 min treated sample exhibited striking competitiveness in terms of comprehensive properties, including a dark current as low as 6 pA, a responsivity of 18.43 A/W, an external quantum efficiency approaching 1 × 10⁴%, a specific detectivity of 2.48 × 10¹⁴ Jones, and a solar-blind/UV rejection ratio close to 1 × 10⁵. Furthermore, the response speed was effectively accelerated because of the reduction on metal/semiconductor interface trap states. Our findings provide a facile, economical, and contamination-free surface passivation technique, which unlocks the potential for comprehensively improving the performance of β-Ga₂O₃ solar-blind metal-semiconductor-metal photodetectors.

Anisotropic luminescence and third-order electric susceptibility of Mg-doped gallium oxide under the half-bandgap edge

Strong anisotropy of photoluminescence of a (100)-cut β-Ga₂O₃ and a Mg-doped β-Ga₂O₃ single crystals was found in UV and visible spectral range, the bands of which were attributed to different types of transitions in the samples. Green photoluminescence in the Mg-doped sample was enhanced approximately twice. A remarkable enhancement of two-photon absorption and self-focusing in β-Ga₂O₃ after doping was revealed by 340-fs laser Z-scanning at 515 nm. The absolute value of complex third order susceptibility χ⁽³⁾ determined from the study increases by 19 times in [001] lattice direction. Saturable absorption and associated self-defocusing were found in the undoped crystal in the [010] direction, which was explained by the anisotropic excitation of F-centers on intrinsic oxygen defects. This effect falls out of resonance in the Mg-doped crystal. The χ⁽³⁾ values which are provided by a decrease of bandgap in Mg-doped β-Ga₂O₃ are χ⁽³⁾ [001] = 1.85·10^-12 esu and χ⁽³⁾ [010]=χ⁽³⁾yyyy = 0.92·10^-12 esu. Our result is only one order of magnitude lower than the best characteristic in green demonstrated by a Mg-doped GaN, which encourages subsequent development of Mg-doped β-Ga₂O₃ as an effective nonlinear optical material in this region.