Feng Xie

Ultra-Low Dark Current AlGaN-Based Solar-Blind Metal–Semiconductor–Metal Photodetectors for High-Temperature Applications

Solar-blind metal-semiconductor-metal (MSM) photodetectors (PDs) with Ni/Au semi-transparent interdigitated contact electrodes are fabricated on Al0.4Ga0.6N epi-layer grown by metal-organic chemical vapor deposition on sapphire substrate. The PD exhibits ultra-low dark current in fA range at room temperature (RT) under 20-V bias and a corresponding breakdown voltage higher than 300 V. The PD also shows a maximum RT quantum efficiency of 64% at ~ 275 nm under 10-V bias with a solar-blind/ultraviolet (UV) rejection ratio up to four orders of magnitude. Even at a high temperature of 150°C, the dark current of the PD is still in fA range with a reasonable rejection ratio of more than 8000, suggesting its potential applications for high-temperature deep-UV detection. The ultra-low dark current achieved is believed to be related to the high-temperature AlN buffer layer used in the epi-structure as well as the coplanar configuration of the MSM PD itself.

Metal–Semiconductor–Metal Ultraviolet Avalanche Photodiodes Fabricated on Bulk GaN Substrate

We report the first demonstration of a GaN-based planar metal-semiconductor-metal (MSM) ultraviolet (UV) avalanche photodiode (APD). The MSM APD with semitransparent interdigitated Schottky electrodes is fabricated on a low-defect-density GaN homoepitaxial layer grown on a bulk GaN substrate by metal-organic chemical vapor deposition. The dislocation density of the GaN homoepilayer characterized by a cathodoluminescence mapping technique is ~ 5 ×106 cm-2. The photodiode exhibits a low dark current density of ~ 1.4 × 10-9 A/cm2 and a high UV-to-visible rejection ratio up to five orders of magnitude under 20-V bias. At high bias, a room-temperature avalanche gain of more than 1100 is achieved under 365-nm UV illumination. The breakdown voltage of the APD shows a positive temperature coefficient of 0.15 V/K, confirming that the high-voltage gain is dominated by the avalanche breakdown mechanism.

Performance comparison of front- and back-illuminated AlGaN-based metal–semiconductor–metal solar-blind ultraviolet photodetectors

In this work, AlGaN-based metal–semiconductor–metal solar-blind ultraviolet photodetectors (PDs) with low dark current were fabricated on sapphire substrates. In both front- and back-illumination operation modes, the PDs exhibited sharp photoresponse cutoffs at ∼280 nm with solar-blind/ultraviolet rejection ratios of more than 103. The quantum efficiency of the back-illuminated PD was observed to generally be higher than that of the front-illuminated PD. Nevertheless, at very low bias range, the front-illuminated PD exhibited greater photoresponsivity. The observed performance differences of the PDs in the different illumination modes are discussed in terms of surface reflectivity and photocarrier collection efficiency.

High quantum efficiency back-illuminated AlGaN-based solar-blind ultraviolet p-i-n photodetectors

AlGaN-based back-illuminated solar-blind ultraviolet (UV) p—i—n photodetectors (PDs) with high quantum efficiency are fabricated on sapphire substrates. To improve the overall performance of the PD, a series of structural design considerations and growth procedures are implemented in the epitaxy process. A distinct wavelength-selective photo-response peak of the PD is obtained in the solar-blind region. When operating in photovoltaic mode, the PD exhibits a solar-blind/UV rejection ratio of up to 4 orders of magnitude and a peak responsivity of ~113.5 mA/W at 270 nm, which corresponds to an external quantum efficiency of ~52%. Under a reverse bias of −5 V, the PD shows a low dark current of ~1.8 pA and an enhanced peak quantum efficiency of ~64%. The thermal noise limited detectivity is estimated to be ~ 3.3 × 1013 cmHz1/2W−1

Bias-Selective Dual-Operation-Mode Ultraviolet Schottky-Barrier Photodetectors Fabricated on High-Resistivity Homoepitaxial GaN

We demonstrate a dual-operation-mode ultraviolet (UV) Schottky-barrier photodetector (PD) fabricated on high-resistivity GaN homoepitaxial layer with low defect density. The undoped GaN active layer is grown by metal-organic chemical vapor deposition on a conductive bulk GaN substrate. Under reverse and zero bias, the PD works in depletion mode with low dark current and high UV/visible rejection ratio. Under forward bias, the PD works alternatively in photoconductive mode, which exhibits high photo-responsivity and an attractive narrow detection band around 365 nm. In addition, the PD also shows reasonable response speed in both operation modes.