Low-dimensional (LD) nanostructures are ideal systems for constructing high-performance photodetectors due to their tailored geometries, high surface-area-to-volume ratios and rationally designed surfaces. This article provides a brief summary about recent progress on LD nanostructures based visible-light-blind ultraviolet photodetectors. The current challenges and an outlook on the future developments of this research field are summarized and highlighted.

Low-dimensional nanostructure ultraviolet photodetectors.

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

In recent years, solar-blind ultraviolet (UV) photodetectors have attracted significant attention from researchers in the field of semiconductor devices due to their indispensable properties in the fields of high-temperature event monitoring, anti-terrorism, security and ad hoc network communication. As an important member of the third-generation semiconductors, β-Ga2O3 is considered to be one of the most promising candidates for solar-blind UV detectors due to its ultra-wide band gap (∼4.9 eV), economic efficiency, high radiation resistance and excellent chemical and thermal stability. Herein, we provide a comprehensive review on Ga2O3-based solar-blind UV photodetectors, with a detailed introduction of the developmental process of material growth methods and device manufacturing in the past decade. We classify the currently reported Ga2O3-based solar-blind UV photodetectors (mainly including photoconductive detectors, heterogeneous PN junction detectors and Schottky junction detectors) and summarize their respective superiorities and potentials for improvement. Finally, considering the actual application requirements, we put forward some meaningful suggestions, including energy band engineering and homogeneous epitaxy, for the future development of Ga2O3 material growth and device manufacturing.

Gallium oxide solar-blind ultraviolet photodetectors: a review

Recent advances in ultraviolet photodetectors

An ultraviolet photodetector was fabricated on MgZnO thin film grown by metal-organic chemical vapor deposition. The peak response of the device centers at 238 nm and cutoff wavelength is 253 nm. The peak responsivity is 129 mA/W at 15 V bias, and the UV/visible reject ratio is 4 orders of magnitude. Internal gain is due to the hole trapping at interface that brings low response speed. Native defects at the Au/MgZnO interface degrade the barrier effect, which caused large dark current and high visible response.

Photoconductive gain in solar-blind ultraviolet photodetector based on Mg0.52Zn0.48O thin film

Cubic Mg0.58Zn0.42O thin films with (100) orientation were grown on cubic MgO substrates. The band gap of the alloy films corresponds to solar blind band. In the case that a MgO buffer layer was employed, the surface roughness was decreased from 38 to 1.6 nm under the same growth conditions. A metal−semiconductor−metal photodetector based on this MgZnO film was fabricated, which showed a low dark current of 0.16 pA and lower sub-bandgap photoresponse than the ones with rougher surface in our early reports.

Mg0.58Zn0.42O Thin Films on MgO Substrates with MgO Buffer Layer

A scanning tunneling microscope (STM) combined with a pump-probe femtosecond terahertz (THz) laser can enable coherence measurements of single molecules. We report THz pump-probe measurements that demonstrate quantum sensing based on a hydrogen (H2) molecule in the cavity created with an STM tip near a surface. Atomic-scale spatial and femtosecond temporal resolutions were obtained from this quantum coherence. The H2 acts as a two-level system, with its coherent superposition exhibiting extreme sensitivity to the applied electric field and the underlying atomic composition of the copper nitride (Cu2N) monolayer islands grown on a Cu(100) surface. We acquired time-resolved images of THz rectification of H2 over Cu2N islands for variable pump-probe delay times to visualize the heterogeneity of the chemical environment at sub-angstrom scale. Description Spatial sensing with hydrogen The coupling of coherent quantum systems to the surrounding environment can be used to create highly sensitive sensors, but many surface-based implementations, such as nitrogen vacancies in diamond, have limited spatial resolution. Wang et al. created a quantum sensor with high spatial sensitivity by using the electric field from a scanning tunneling microscope tip to confine a hydrogen molecule on copper nitride islands grown on a copper surface. Femtosecond-pulse terahertz spectroscopy was used to follow the coherence of the two-level system created by different adsorption geometries. The temporal oscillations and decoherence in the superposition state showed spatial variations at the sub-angstrom scale. —PDS The coherent superposition of two low-lying states of hydrogen is extremely sensitive to its local spatial environment.

Atomic-scale quantum sensing based on the ultrafast coherence of an H2 molecule in an STM cavity

A growing and preparing method of a cubic phase oxygen zinc magnesium single crystal film belongs to the technical field of semiconductor photoelectric material preparation. In the method, an LP-MOCVD method is utilized to grow a cubic phase MgZnO film at low-temperature and oxygen-enrichment conditions; the growing conditions are as follows: sapphire and magnesium oxide are selected as substrates; the pressure of a growth chamber is 2*104Pa; the growth temperature is 280-450 DEG C; the carrier gas is 99.999% nitrogen; MCp2Mg is used as a magnesium source, the temperature of the magnesium source is controlled at 40-50 DEG C, and the molar flow is 18-40 mu mol/min; DEZn is used as a zinc source, the temperature thereof is controlled at -5 DEG C, and the molar flow is 0.45-3 mu mol/min; and the high-purity oxygen is used as an oxygen source, and the molar flow thereof is 0.07 mol/min, thus the proportion of the II-VI groups is far less than 1. The cubic phase oxygen zinc magnesium single crystal film prepared by the invention has high crystallization quality and good repeatability; and the coverage area of absorption edges of the film is 200-280nm.

Likun Wang

Papers

Photoconductive gain in solar-blind ultraviolet photodetector based on Mg0.52Zn0.48O thin film

Mg0.58Zn0.42O Thin Films on MgO Substrates with MgO Buffer Layer

Atomic-scale quantum sensing based on the ultrafast coherence of an H2 molecule in an STM cavity

Growing and preparing method of cubic phase oxygen zinc magnesium single crystal film

Structural, optical and electrical properties of r-TiO2:Sn/SnO2:(F/Nb) tandem film by aerosol-assisted chemical vapor deposition