GaN-based Ultraviolet Photodetectors Research Articles

Photoelectric properties and persistent photoconductivity of GaN-based ultraviolet photodetectors

Persistent photoconductivity deeply affects the performance of the photodetector, and has been studied in a variety of semiconductor optoelectronic devices. In this work, AlGaN/GaN metal-heterojunction-metal (MHM) ultraviolet (UV) detectors and GaN metal-semiconductor-metal (MSM) ultraviolet detectors were prepared using transverse Schottky contacts, and characterized at different temperatures, light intensity and bias voltage. The two-dimensional electron gas (2-DEG) at the Schottky heterojunction of AlGaN and GaN is used to generate high-speed electron mobility, which significantly improves the response speed and responsivity of photogenerated carriers. Under the illumination of 365 nm center ultraviolet light with an intensity of 4.4 mW/cm2, the photocurrent can reach 434 μA-MHM and 38 μA-MSM (25 °C), and the attenuation rate increase by 2.8 times, 5 times and 3.7 times with temperature (25 °C-250 °C), bias voltage (5/10/15 V), and light intensity (0.33/1.1/4.4 mW/cm2), respectively, and the attenuation rate reaches 50∼80 times.

Dislocation density control of GaN epitaxial film and its photodetector

At present, GaN-based ultraviolet photodetectors (UV PDs) is confronted with the challenge of high dark current and low responsivity. In this work, we designed and prepared high-performance GaN-based UV PDs on the sapphire substrates by the combination of low-temperature pulsed laser deposition (LT-PLD) and high-temperature metal-organic chemical vapor deposition growth (HT-MOCVD). The as-grown GaN film shows high-crystalline with edge dislocation density of 6.50 × 107 cm−2 and screw dislocation density of 1.92 × 108 cm−2, respectively. Furthermore, the optimized electrode structure has been well designed to enhance the carrier transport characteristics in GaN-based UV PDs, which improves the performance of GaN-based UV PDs accordingly. Based on the high-quality GaN film and the optimized electrode structure, high-performance GaN-based UV PDs are fabricated, which reveals the very high responsivity and small dark current of 1.4 A/W and 4.8 nA@5V, respectively. These high-performance GaN-based UV PDs shed light on the potential application in UV warning.

High gain GaN ultraviolet Schottky photodetector with Al-doped ZnO interlayer

We fabricated an GaN Schottky photodiode (PD) with Al-doped ZnO (AZO) interlayer for ultraviolet (UV) photodetection, and its optoelectrical properties with a comparison to the GaN Schottky PD without AZO interlayer. The AZO-interlayered GaN Schottky PD was highly sensitive to 350 nm laser irradiation, having a photoresponsivity of 11.1 AW–1 and detectivity of 1.04 × 1012 cm·Hz1/2·W–1 at -2 V as against 0.28 AW−1 and 2.23 × 1010 cm·Hz1/2·W–1 for the GaN Schottky PD without AZO interlayer. The transient photoresponse revealed a rise and decay time of 203 and 293 ms, respectively for the AZO-interlayered GaN Schottky PD. The introduction of AZO interlayer resulted in a reduction in the noise spectral density, leading to an increase in the detectivity by more than an order, as compared to GaN Schottky PD without AZO interlayer. An improved photodetection behavior of the AZO-interlayered GaN Schottky PD could be ascribed to effective GaN surface passivation and reduction of the surface states by the AZO interlayer. The utilization of the AZO in GaN-based UV photodetectors can provide a potential and simplistic approach towards the fabrication of high performance GaN-based UV photodetectors.

Defect effect on the performance of nonpolar GaN-based ultraviolet photodetectors

The anisotropy of GaN(11-20) makes it possible to fabricate polarized ultraviolet (UV) photodetectors (PDs) for applications in fields such as remote sensing and airborne astronomical navigation. The defect density has a significant effect on the performance of GaN(11-20)-based UV PDs. However, the mechanism through which different defects and their densities affect the performance of these devices is unclear. Therefore, in this work, we investigated the mechanisms of the screw or mixed dislocation, edge dislocation, and basal stacking fault (BSF) densities affecting the dark current, responsivity, and response time of GaN (11-20)-based PDs, respectively. We observed that the screw or mixed dislocation increased the dark current mainly through reducing the Schottky barrier height and forming leakage current, whereas the edge dislocation and BSF decreased the responsivity by reducing the electron mobility. Furthermore, all the three types of defects increased the response time through forming traps to recombine the holes with electrons and thus delaying the escape of carriers. These results are highly significant for developing nonpolar GaN-based UV PDs.

NiO/GaN p-n junction ultraviolet photodetector and self-powered technology

<sec> Ultraviolet photodetector plays an important role in fire warning, missile tracking and dose detecting of ultraviolet sterilization and disinfection, which is closely related to human lives. With the development of integrated detection system, the requirements for the size and energy consumption of the detector are becoming more and more stringent. Traditional detector that requires an external power supply can no longer meet these requirements. Moreover, a traditional ultraviolet detector is mainly composed of first-generation semiconductors and second-generation semiconductors. These semiconductors have small band gaps and large cut-off wavelengths, and are more suitable for infrared detection. When used for implementing the ultraviolet detection, an additional layer is often required, which increases not only the volume but also the cost. </sec><sec> Gallium nitride (GaN), as a third-generation semiconductor, has a band gap of 3.4 eV and a corresponding absorption edge of 365 nm. It is a natural ultraviolet detection material. At the same time, the excellent physical and chemical properties make the devices prepared by GaN have high stability. In recent years, some studies have shown that the GaN-based ultraviolet photodetectors have excellent responsiveness, but each of these detectors usually requires an external bias and has a slow response speed. Here, we propose a high responsivity, fast response speed and self-powered ultraviolet photodetector based on NiO/GaN p-n junction. By using the magnetron sputtering, a layer of 70 nm thick p-NiO film is deposited on a high-quality n-GaN film that has been grown on a sapphire substrate by the metal-organic chemical vapor deposition. The fabricated p-n junction shows obvious rectification characteristics at ± 0.5 V. Due to the existence of the built-in electric field, the device can work without externally applied bias. Under zero bias, the detector shows a responsivity of 272.3 mA/W for 365 nm ultraviolet light while the intensity is 50 μW/cm<sup>2</sup>, and has a detectivity as high as 2.83 × 10<sup>14</sup> Jones. This indicates that the detector has a high sensitivity even for very weak light. Owing to the good crystallinity of the film, the dark current is as low as 10<sup>–10</sup> A, the switching ratio is > 10<sup>3</sup>, and the response speed reaches 31 ms. These excellent properties show the broad application prospects of the devices based on NiO/GaN p-n junctions in the field of self-powered ultraviolet detection, and thus providing new ideas for the future development of intelligent integration. </sec>

Facile method for reducing decay time in GaN-based ultraviolet photodetector using microheater

Gallium nitride (GaN), a wide-bandgap Ⅲ–Ⅴ compound semiconductor, is currently regarded as a promising material for ultraviolet (UV) photodetectors. However, persistent photoconductivity (PPC) attributed to deep-level defects has been widely reported. This undesirable phenomenon is one of the most challenging issues and needs to be solved to commercialize the material as a reliable device in the future. In this study, a facile method is suggested to suppress the PPC for the rapid recovery of the dark-current level in GaN-based UV photodetectors by employing an additional microheater on the device. Through Joule heating, thermal energy is supplied to the GaN film to accelerate the carrier capture rate. For the transient current measurements, the decay time of the microfabricated device was calculated and compared after exposure to 365-nm UV illumination at various heater powers (thermal heating sources) simultaneously. As a result, a 99% decrease in decay time was measured (∼11501s for 0 W and ∼84 s for 2.002 W). Based on these results, a facile method was developed in this study to suppress PPC in a reliable device by simple device heating.

Ultra-thin GaN nanostructures based self-powered ultraviolet photodetector via non-homogeneous Au-GaN interfaces

We report the fabrication of ultra-thin GaN (0002) nanostructures based self-powered ultraviolet photodetector on Si (111) substrate. Non-homogeneous GaN nano-islands were perceived on Si surface with a thickness of ~30 nm and an average distribution density of 2 × 1010 cm−2. Even at low dimension GaN-nanostructures film, the capability of ultraviolet detection of fabricated photodetector added novelty to this work, where performance parameters such as photosensitivity (~102), detectivity (~109 Jones), responsivity (1.76 mA/W) and noise equivalent power (3.5 × 10−11 WHz−1/2) under self-powered mode were observed. The transient photo-response measurement revealed a rapid rise and decay time constants of ~18 ms and ~27 ms respectively. Under varying optical power (1 mW–13 mW), the GaN photodetector displayed significant enhancement in photocurrent with increasing optical power. The performance of the fabricated detector has been also analysed under varying bias voltage where it revealed significantly enhanced responsivity (23 fold) and detectivity (~1000 fold). Such nanostructured self-powered GaN-based ultraviolet photodetector paves the way towards the fabrication of energy-efficient optoelectronic devices.

An Analysis of GaN-based Ultraviolet Photodetector

The GaN-based UV photodetectors have been a hot topic in semiconductor field. To present the existing research, this paper introduces the development of GaN-based UV photodetectors and the common types of detectors. The difficulties and new technologies of UV photodetector are also introduced. About the difficulties, the whole paper would focus on the substrate of the GaN. To solve this problem, this paper have introduced the PSS, an enhancement of sapphire substrate. Also this paper have put a hypothesis on the shape of PSS. The surface plasmon, which is not a common technology in photodetectors is also introduced. It is hoped that this paper will provide research background and direction for researchers who want to enter this field.

High-Performance Self-Powered Ultraviolet Photodetector Based on Nano-Porous GaN and CoPc p-n Vertical Heterojunction.

Gallium nitride (GaN) is a superior candidate material for fabricating ultraviolet (UV) photodetectors (PDs) by taking advantage of its attractive wide bandgap (3.4 eV) and stable chemical and physical properties. However, the performance of available GaN-based UV PDs (e.g., in terms of detectivity and sensitivity) still require improvement. Fabricating nanoporous GaN (porous-GaN) structures and constructing organic/inorganic hybrids are two effective ways to improve the performance of PDs. In this study, a novel self-powered UV PD was developed by using p-type cobalt phthalocyanine (CoPc) and n-type porous-GaN (CoPc/porous-GaN) to construct a p–n vertical heterojunction via a thermal vapor deposition method. Under 365 nm 0.009 mWcm−2 light illumination, our device showed a photoresponsivity of 588 mA/W, a detectivity of 4.8 × 1012 Jones, and a linear dynamic range of 79.5 dB, which are better than CoPc- and flat-GaN (CoPc/flat-GaN)-based PDs. The high performance was mainly attributed to the built-in electric field (BEF) generated at the interface of the CoPc film and the nanoporous-GaN, as well as the nanoporous structure of GaN, which allows for a higher absorptivity of light. Furthermore, the device showed excellent stability, as its photoelectrical property and on/off switching behavior remained the same, even after 3 months.

Sol-gel-derived gallium nitride thin films for ultraviolet photodetection

PurposeThis study aims to explore the applicability of the sol-gel-derived GaN thin films for UV photodetection.Design/methodology/approachGaN-based ultraviolet (UV) photodetector with Pt Schottky contacts was fabricated and its applicability was investigated. The current-voltage (I-V) characteristics of the GaN-based UV photodetector under the dark current and photocurrent were measured.FindingsThe ideality factors of GaN-based UV photodetector under dark current and photocurrent were 6.93 and 5.62, respectively. While the Schottky barrier heights (SBH) for GaN-based UV photodetector under dark current and photocurrent were 0.35 eV and 0.34 eV, respectively. The contrast ratio and responsivity of this UV photodetector measured at 5 V were found to be 1.36 and 1.68 μA/W, respectively. The photoresponse as a function of time was measured by switching the UV light on and off continuously at different forward biases of 1, 3 and 6 V. The results showed that the fabricated UV photodetector has reasonable stability and repeatability.Originality/valueThis work demonstrated that GaN-based UV photodetector can be fabricated by using the GaN thin film grown by low-cost and simple sol-gel spin coating method.

High responsivity and low dark current nonpolar GaN-based ultraviolet photo-detectors

Nonpolar a-plane GaN-based metal-semiconductor–metal UV PDs, with high responsivity and low dark current, were made from a-plane GaN epitaxial films grown on r-plane sapphire by controlling the dislocation density.

Irradiation Response of Graphene Enhanced Gallium Nitride Metal-Semiconductor-Metal Ultraviolet Photodetectors

ABSTRACTRadiation-tolerant materials, sensors and electronics can enable lightweight space subsystems with reduced packaging requirements and increased operation lifetimes. Such technology can be used within extreme harsh environments related to space exploration, radiation medicine and power generation (combustion and nuclear). Gallium nitride (GaN), a ceramic semiconductor material, is a candidate material due to its stability within high-radiation, high-temperature and chemically corrosive environments. In addition, the wide bandgap of GaN (3.4 eV) can be leveraged for ultraviolet (UV) wavelength photodetection. In metal-semiconductor-metal (MSM) photodetector architectures using Schottky contacts, transparent electrodes (e.g., graphene) can increase sensitivity and improve overall device response. Here we present fabrication and characterization of GaN-based UV photodetectors using graphene electrodes irradiated up to 200 krad total ionizing dose (TID) then tested under UV light and dark conditions. For current-voltage measurements taken at 90, 120 and 200 krad TID, the current-voltage response does not vary significantly. From 90 to 120 krad TID, the responsivity shifts by 2% before dropping off at 200 krad TID. These initial findings suggest that graphene/GaN MSM UV photodetectors can provide robust operation within extreme harsh environments.

GaN-Based Schottky Barrier Photodetectors With a 12-Pair Mg$_{\rm x}$N$_{\rm y}$–GaN Buffer Layer

GaN-based ultraviolet (UV) photodetectors (PDs) separately prepared with a conventional single low-temperature (LT) GaN buffer layer and a 12-pair MgxNy-GaN buffer layer were both fabricated. It was found that we could reduce threading dislocation (TD) density and thus improve crystal quality of the GaN-based UV PDs by using the 12-pair MgxNy-GaN buffer layer. With a -2-V applied bias, it was found that the reverse leakage currents measured from PDs with a single LT GaN buffer layer and that with a 12-pair MgxNy-GaN buffer layer were 4.57 times 10-6 and 1.44 times 10-12 A, respectively. It was also found that we could use the 12-pair MgxNy-GaN buffer layer to suppress photoconductive gain, enhance UV-to-visible rejection ratio, reduce noise level, and enhance the detectivity.

A new Schottky barrier structure of GaN-based ultraviolet photodetector

A new GaN-based ultraviolet photodetector with Schottky barrior structure is proposed. Comparied with the conventional i-GaN/n+-GaN structure，there is an additional thin n-AlGaN cap layer on the i-GaN in the new structure. The simulation result demonstrates that the new structure leads to an increased quantum efficiency in GaN photodetection，since the negative effect of surface states on the photodetector is reduced in the new structure. In addition，it is suggested that the performance of device with the new structure could be further improved by employing an even thinner AlGaN cap layer with higher carrier concentration.

Dark current characteristics of thermally treated contacts on GaN-based ultraviolet photodetectors

The III–V nitrides (GaN and AlGaN) are being actively investigated recently for its potential as ultraviolet (UV) photodetector materials. One of the most important considerations in fabricating a photodetector is achieving a low dark current condition, which is critical in producing UV photodetectors with a high signal-to-noise ratio. For this purpose, thermal treatment has been proven to be a useful method in reducing the leakage current in a Schottky contact, as well as reducing the dark current in a Schottky contact based metal–semiconductor–metal (MSM) photodetector. In this work, GaN based MSM photodetectors (photodiodes) with nickel (Ni) Schottky contacts were fabricated and characterized. The application of thermal treatment to the contacts at various annealing temperatures (400–700 °C) was investigated. Cryogenic cooling after heat treatment was also performed to determine the effects of this treatment on the electrical characteristics of the devices. Electrical and morphological characterization was performed by current–voltage ( I– V) and atomic force microscopy (AFM) measurements, respectively.

High-speed pin ultraviolet photodetectors fabricated on GaN

The authors report very high-speed GaN-based ultraviolet photodetectors using a pin device structure. The best devices have rise times of ~90 ps and bandwidths of ~1.6 GHz at –30 V. This is the fastest speed for a GaN-based photodetector reported to date.