Ag2O/β-Ga2O3 Heterojunction-Based Self-Powered Solar Blind Photodetector with High Responsivity and Stability

Highly Wavelength-Selective Self-Powered Solar-Blind Ultraviolet Photodetector Based on Colloidal Aluminum Nitride Quantum Dots

Colloidal quantum dots are semiconductor nanocrystals endowed with unique optoelectronic properties. A major challenge to the field is the lack of methods for synthesizing quantum dots exhibit strong photo-response in the deep-ultraviolet (DUV) band. Here, a facile solution-processed method is presented for synthesizing ultrawide bandgap aluminium nitride quantum dots (AlN QDs) showing distinguished UV-B photoluminescence. Combined with the strong optical response in solar blind band, a solution-processed, self-powered AlN-QDs/β-Ga2O3 solar-blind photodetector is demonstrated. The photodetector is characterized with a high responsivity of 1.6 mA W-1 under 0 V bias and specific detectivity 7.60 × 10-11 Jones under 5 V bias voltage with good solar blind selectivity. Given the solution-processed capability of the devices and extraordinary properties of AlN QDs, this study anticipates the utilization of AlN QDs will open up unique opportunities for cost-effective industrial production of high-performance DUV optoelectronics for large-scale applications.

Ultrahigh Photoresponsivity of W/Graphene/β-Ga2O3 Schottky Barrier Deep Ultraviolet Photodiodes

The integration of graphene with semiconductor materials has been studied for developing advanced electronic and optoelectronic devices. Here, we propose ultrahigh photoresponsivity of β-Ga2O3 photodiodes with a graphene monolayer inserted in a W Schottky contact. After inserting the graphene monolayer, we found a reduction in the leakage current and ideality factor. The Schottky barrier height was also shown to be about 0.53 eV, which is close to an ideal value. This was attributed to a decrease in the interfacial state density and the strong suppression of metal Fermi-level pinning. Based on a W/graphene/β-Ga2O3 structure, the responsivity and external quantum efficiency reached 14.49 A/W and 7044%, respectively. These values were over 100 times greater than those of the W contact alone. The rise and delay times of the W/graphene/β-Ga2O3 Schottky barrier photodiodes significantly decreased to 139 and 200 ms, respectively, compared to those obtained without a graphene interlayer (2000 and 3000 ms). In addition, the W/graphene/β-Ga2O3 Schottky barrier photodiode was highly stable, even at 150 °C.

Enhancing Performance of Ultraviolet C Photodetectors Through Single-Domain Epitaxy of Monoclinic β-Ga2 O3 Films and Tailored Anti-Reflection Coating

Implementing high-performance ultraviolet C photodetectors (UVC PDs) based on β-Ga2 O3 films is challenging owing to the anisotropic crystal symmetry between the epitaxial films and substrates. In this study, highly enhanced state-of-the-art photoelectrical performance is achieved using single-domain epitaxy of monoclinic β-Ga2 O3 films on a hexagonal sapphire substrate. Unlike 3D β-Ga2 O3 films with twin domains, 2D β-Ga2 O3 films exhibit a single domain with a smooth surface and low concentration of point defects, which enable efficient charge separation by suppressing boundary-induced recombination. Furthermore, a tailored anti-reflection coating (ARC) is adopted as a light-absorbing medium to improve charge generation. The tailored nanostructure, which features a gradient refractive index, not only substantially reduces the reflection, but also suppresses the surface leakage current as a passivation layer. This study provides fundamental insights into the single-domain epitaxy of β-Ga2 O3 films and the application of ARC for the development of high-performance UVC PDs.

Rapid Response Solar Blind Deep UV Photodetector with High Detectivity Based On Graphene:N/βGa2 O3 :N/GaN p-i-n Heterojunction Fabricated by a Reversed Substitution Growth Method

This work reports a high-detectivity solar-blind deep ultraviolet photodetector with a fast response speed, based on a nitrogen-doped graphene/βGa₂ O₃ /GaN p-i-n heterojunction. The i layer of βGa₂ O₃ with a Fermi level lower than the central level of the forbidden band of 0.2 eV is obtained by reversed substitution growth with oxygen replacing nitrogen in the GaN matrix, indicating the majority carrier is hole. X-ray diffractometershows that the transformation of GaN into βGa₂ O₃ with (-201) preferred orientation at temperature above 900 °C in an oxygen ambient. The heterojunction shows enhanced self-powered solar blind detection ability with a response time of 3.2 µs (rise)/0.02 ms (delay) and a detectivity exceeding 10¹² Jones. Under a reverse bias of -5 V, the photoresponsivity is 8.3 A W^-1 with a high I_light /I_dark ratio of over 10⁶ and a detectivity of ≈9 × 10¹⁴ Jones. The excellent performance of the device is attributed to 1) the continuous conduction band without a potential energy barrier, 2) the larger built-in potential in the heterojunction because of the downward shift of Fermi energy level in β-Ga₂ O₃ , and 3) an enhanced built-in electric field in the βGa₂ O₃ due to introducing p-type graphene with a high hole concentration of up to ≈10²⁰ cm^-3 .

Enhanced Responsivity and Optoelectronic Properties of Self-Powered Solar-Blind Ag2O/β-Ga2O3 Heterojunction-Based Photodetector with Ag:AZO Co-Sputtered Electrode

A Ag:AZO electrode was used as an electrode for a self-powered solar-blind ultraviolet photodetector based on a Ag₂O/β-Ga₂O₃ heterojunction. The Ag:AZO electrode was fabricated by co-sputtering Ag and AZO heterogeneous targets using the structural characteristics of a Facing Targets Sputtering (FTS) system with two-facing targets, and the electrical, crystallographic, structural, and optical properties of the fabricated thin film were evaluated. A photodetector was fabricated and evaluated based on the research results that the surface roughness of the electrode can reduce the light energy loss by reducing the scattering and reflectance of incident light energy and improving the trapping phenomenon between interfaces. The thickness of the electrodes was varied from 20 nm to 50 nm depending on the sputtering time. The optoelectronic properties were measured under 254 nm UV-C light, the on/off ratio of the 20 nm Ag:AZO electrode with the lowest surface roughness was 2.01 × 10⁸, and the responsivity and detectivity were 56 mA/W and 6.99 × 10¹¹ Jones, respectively. The Ag₂O/β-Ga₂O₃-based solar-blind photodetector with a newly fabricated top electrode exhibited improved response with self-powered characteristics.

A Self-Powered High-Responsivity, Fast-Response-Speed Solar-Blind Ultraviolet Photodetector Based on CuO/β-Ga2O3 Heterojunction with Built-In Potential Control

Controlling built-in potential can enhance the photoresponse performance of self-powered photodetectors. Among the methods for controlling the built-in potential of self-powered devices, postannealing is simpler, more efficient, and less expensive than ion doping and alternative material research. In this study, a CuO film was deposited on a β-Ga₂O₃ epitaxial layer via reactive sputtering with an FTS system, and a self-powered solar-blind photodetector was fabricated through a CuO/β-Ga₂O₃ heterojunction and postannealed at different temperatures. The postannealing process reduced the defects and dislocations at the interface between each layer and affected the electrical and structural properties of the CuO film. After postannealing at 300 °C, the carrier concentration of the CuO film increased from 4.24 × 10¹⁸ to 1.36 × 10²⁰ cm^-3, bringing the Fermi level toward the valence band of the CuO film and increasing the built-in potential of the CuO/β-Ga₂O₃ heterojunction. Thus, the photogenerated carriers were rapidly separated, increasing the sensitivity and response speed of the photodetector. The as-fabricated photodetector with 300 °C postannealing exhibited a photo-to-dark current ratio of 1.07 × 10³; responsivity and detectivity of 30.3 mA/W and 1.10 × 10¹² Jones, respectively; and fast rise and decay times of 12 ms and 14 ms, respectively. After three months of storage in an open-air space, the photocurrent density of the photodetector was maintained, indicating good stability with aging. These results suggest that the photocharacteristics of CuO/β-Ga₂O₃ heterojunction self-powered solar-blind photodetectors can be improved through built-in potential control using a postannealing process.