New concept ultraviolet photodetectors

A novel self-powered UV photodetector based on electrospun ZnO nanofiber arrays is introduced. Aligned pure ZnO nanofibers and Ag-doped p-type ZnO nanofibers are processed perpendicular to each other, and p-n junction arrays of ZnO nanofibers are fabricated as a result. Owing to the intrinsic intervals between nanofibers, the device is fully transparent on quartz substrate. Various characterization methods including TEM, XRD, and XPS are used to testify the existence form of Ag element in ZnO nanofibers, and a field effect transistor is constructed to judge their conductivity. It is discovered that the Ag doping process not only transforms ZnO to p-type conductivity, making it possible to build this self-powered photodetector, but also forms Ag nanoparticles in ZnO nanofibers and thus helps reduce the response time. Benefiting from the abovementioned dual effects, this UV detector is found to have an enhanced performance, with the on-off ratio up to 104 at zero bias and a rather short rise/decay time of 3.90 s/4.71 s.

Novel Transparent and Self-Powered UV Photodetector Based on Crossed ZnO Nanofiber Array Homojunction

Based on electronic structure and atomic size considerations, nitrogen has been regarded as the most suitable impurity for p-type doping in ZnO. However, numerous experimental efforts by many different groups have not resulted in stable and reproducible p-type material, casting doubt on the efficacy of nitrogen as a shallow acceptor. Based on advanced first-principles calculations we find that nitrogen is actually a deep acceptor, with an exceedingly high ionization energy of 1.3 eV, and hence cannot lead to hole conductivity in ZnO. In light of this result, we reexamine prior experiments on nitrogen doping of ZnO.

http://absimage.aps.org/image/MAR10/MWS_MAR10-2009-001476.pdf

Why nitrogen cannot lead to p-type conductivity in ZnO

Because of the direct band gap of 4.9 eV, β-Ga2O3 has been considered as an ideal material for solar-blind photodetection without any bandgap tuning. Practical applications of the photodetectors require fast response speed, high signal-to-noise ratio, low energy consumption and low fabrication cost. Unfortunately, most reported β-Ga2O3-based photodetectors usually possess a relatively long response time. In addition, the β-Ga2O3 photodetectors based on bulk, the individual 1D nanostructure, and the film often suffer from the high cost, the low repeatability, and the relatively large dark current, respectively. In this paper, a Au/β-Ga2O3 nanowires array film vertical Schottky photodiode is successfully fabricated by a simple thermal partial oxidation process. The device exhibits a very low dark current of 10 pA at −30 V with a sharp cutoff at 270 nm. More interestingly, the 90–10% decay time of our device is only around 64 μs, which is much quicker than any other previously reported β-Ga2O3-based photodet...

Self-Powered Solar-Blind Photodetector with Fast Response Based on Au/β-Ga2O3 Nanowires Array Film Schottky Junction

Due to its significant applications in many relevant fields, light detection in the solar-blind deep-ultraviolet (DUV) wavelength region is a subject of great interest for both scientific and industrial communities. The rapid advances in preparing high-quality ultrawide-bandgap (UWBG) semiconductors have enabled the realization of various high-performance DUV photodetectors (DUVPDs) with different geometries, which provide an avenue for circumventing numerous disadvantages in traditional DUV detectors. This article presents a comprehensive review of the applications of inorganic UWBG semiconductors for solar-blind DUV light detection in the past several decades. Different kinds of DUVPDs, which are based on varied UWBG semiconductors including Ga2O3, MgxZn1−xO, III-nitride compounds (AlxGa1−xN/AlN and BN), diamond, etc., and operate on different working principles, are introduced and discussed systematically. Some emerging techniques to optimize device performance are addressed as well. Finally, the existing techniques are summarized and future challenges are proposed in order to shed light on development in this critical research field.

Recent Progress in Solar-Blind Deep-Ultraviolet Photodetectors Based on Inorganic Ultrawide Bandgap Semiconductors

We demonstrate a novel type of ZnO self-powered photodetector based on the asymmetric metal-semiconductor-metal (MSM) structure: one Au interdigitated electrode with wide fingers and the other one with narrow fingers. These ZnO photodetectors exhibit attractive photovoltaic characteristics at 0 V bias. More interestingly, with increasing the asymmetric ratio (the width of wide fingers : the width of narrow fingers) of the interdigitated electrodes, the responsivity of the ZnO self-powered UV photodetectors was enhanced obviously, reaching as high as 20 mA W−1 when the asymmetric ratio was 20 : 1. A physical model based on band energy theory was developed to illustrate the origin of the photoresponse at 0 V in our device. Our findings provide a new route to realizing self-powered photodetectors.

Realization of A Self-Powered ZnO MSM UV Photodetector with High Responsivity Using An Asymmetric Pair of Au Electrodes

Light-emitting diodes fabricated from small-size ZnO quantum dots

A hybrid perovskite MAPbCl3 (MA = CH3NH3+) single crystal is considered to be one of the most viable candidates for the development of photodetectors because of its outstanding optoelectronic properties. However, the relatively lower crystalline quality of the reported MAPbCl3 single crystals fabricated by the traditional one-step inverse temperature crystallization results in momentous degradation in the performance of their photodetectors. Here, we present a novel two-step temperature process to fabricate high-quality MAPbCl3 single crystals, namely, lower temperature nucleation and higher temperature crystallization. These MAPbCl3 single crystals present low defect density (∼7.9 × 109 cm-3) commensurate with the best-quality crystals of hybrid organic-inorganic lead halide perovskites reported so far. Moreover, a high-performance ultraviolet photodetector was demonstrated on MAPbCl3 single crystals. At 30 V, the peak responsivity at 415 nm of the photodetector is as high as 3.73 A W-1 (light intensity = 1 mW cm-2), ∼2-3 orders of magnitude higher than that of the previously reported MAPbCl3 photodetectors. Meanwhile, the device has an ultrafast response speed with a rise time of 130 ns, which is one of the shortest values of MAPbX3-based photodetectors. Our findings open a new way to obtain high-quality perovskite single crystals and their high-performance photodetectors.

High-Performance Planar-Type Ultraviolet Photodetector Based on High-Quality CH 3 NH 3 PbCl 3 Perovskite Single Crystals

Metal–semiconductor–metal structured photodetectors based on β-Ga2O3 thin films were fabricated. Because of the high dark-resistance and considerable photoconduction, extremely uneven distribution ...

Avalanche Gain in Metal–Semiconductor–Metal Ga2O3 Solar-Blind Photodiodes

A high performance p-GaN/n-ZnMgO heterojunction photodiode was demonstrated and investigated. A high quality p-GaN film was grown on GaN/sapphire templates by plasma-assisted molecular beam epitaxy and subsequently an n-ZnMgO layer was deposited on p-GaN by a metal organic chemical vapor deposition technique. The p-GaN/n-ZnMgO heterojunction photodetector shows a clear rectifying I–V characteristic with a turn-on voltage of 2.5 V. At zero-bias voltage, the device shows a high peak responsivity of 196 mA W−1 at 362 nm. The 10–90% rise time and 90–10% decay time of the device can be as short as 1.7 ms and 3.3 ms, respectively. The excellent crystal quality and electrical properties of p-GaN play an important role in the high performance of the photodiode. This work provides a feasible way for the development of high-performance heterojunction self-powered UV detectors.

Xiuhua Xie

Papers

Realization of A Self-Powered ZnO MSM UV Photodetector with High Responsivity Using An Asymmetric Pair of Au Electrodes

Light-emitting diodes fabricated from small-size ZnO quantum dots

High-Performance Planar-Type Ultraviolet Photodetector Based on High-Quality CH 3 NH 3 PbCl 3 Perovskite Single Crystals

Avalanche Gain in Metal–Semiconductor–Metal Ga2O3 Solar-Blind Photodiodes

A high performance self-powered ultraviolet photodetector based on a p-GaN/n-ZnMgO heterojunction