High-performance metal-semiconductor-metal deep-ultraviolet photodetectors based on homoepitaxial diamond thin film

Cataloged from PDF version of article.We report on the design, fabrication, and characterization of solar-blind Schottky photodiodes with low noise and high detectivity. The devices were fabricated on n-/n+ AlGaN/GaN heterostructures using a microwave compatible fabrication process. True solar-blind operation with a cutoff wavelength of similar to274 nm was achieved with Al(x)Ga(1-x)N (x=0.38) absorption layer. The solar-blind detectors exhibited <1.8 nA/cm(2) dark current density in the 0-25 V reverse bias regime, and a maximum quantum efficiency of 42% around 267 nm. The photovoltaic detectivity of the devices were in excess of 2.6x10(12) cm Hz(1/2)/W, and the detector noise was 1/f limited with a noise power density less than 3x10(-29) A(2)/Hz at 10 kHz. (C) 2002 American Institute of Physics

We report high performance visible-blind GaN-based p-i-n photodetectors grown by metal-organic chemical vapor deposition on c -plane sapphire substrates. The dark current of the 200 μm diameter devices was measured to be lower than 20 pA for bias voltages up to 5 V. The breakdown voltages were higher than 120 V. The responsivity of the photodetectors was ∼0.23 AW at 356 nm under 5 V bias. The ultraviolet-visible rejection ratio was 6.7× 103 for wavelengths longer than 400 nm. © 2008 American Institute of Physics

We experimentally investigated the influence of positional disorder on the photonic band gap, defect characteristics, and waveguiding in two-dimensional dielectric and metallic photonic crystals. Transmission measurements performed on the dielectric photonic crystals have shown a stop band even if a large amount of disorder was introduced to these structures. On the other hand, the photonic band gap of the metallic crystals was found to be very sensitive to disorder, while the metallicity gap was not affected significantly. We addressed how the transmission characteristics of a cavity were affected in the presence of weak disorder. Since the translational symmetry was broken by disorders, we measured different cavity frequencies when we generated defects at various locations. We also demonstrated the propagation of photons by hopping through coupled-cavity structures in both dielectric and metallic two-dimensional photonic crystals. Effects of weak disorder on guiding and bending of electromagnetic waves through the coupled-cavity waveguides were also investigated.

The authors report high performance solar-blind photodetectors with reproducible avalanche gain as high as 1560 under ultraviolet illumination. The solar-blind photodetectors have a sharp cutoff around 276 nm. The dark currents of the 40 m diameter devices are measured to be lower than 8 fA for bias voltages up to 20 V. The responsivity of the photodetectors is 0.13 A / W at 272 nm under 20 V reverse bias. The thermally limited detectivity is calculated as D * = 1.4 ϫ 10 14 cm Hz 1/2 W −1 for a 40 m diameter device.The recent developments in high Al-content Al x Ga 1−x N material growth technology made it possible to fabricate high performance solar-blind photodetectors operating in the ultraviolet ͑UV͒ spectral region with improved receiver sensitivity, low noise, low dark current density, and high speed. 1-3 AlGaN-based Schottky, p-i-n, and metalsemiconductor-metal photodetectors with very high performances have already been demonstrated. 4,5 The UV-filtering nature of the atmospheric ozone molecules blocks the solar radiation to reach the earth's surface for wavelengths shorter than 280 nm. In this case, UV photodetectors with cutoff wavelengths around 280 nm, which are also called solarblind detectors, can detect very weak UV signals under intense background radiation. These devices have important applications including missile plume detection, chemical/ biological agent sensing, flame alarms, covert space-to-space and submarine communications, ozone-layer monitoring, and gas detection. Due to their high responsivity ͑Ͼ600 A / W͒, high speed, high cathode gain ͑on the order of a million͒, and low dark current properties, photomultiplier tubes ͑PMTs͒ are frequently used in such applications. However, PMTs are very expensive and bulky. Besides, they require a cooling system, and they have high operation voltages in excess of 1000 V. To achieve solar-blind detection, PMTs should also be integrated with complex and expensive filters. In order to avoid these disadvantages, high performance solid-state UV photodetectors with high internal gain are needed. 6 Wide band-gap semiconductor photodetectors, such as Al x Ga 1−x N with x = 0.4, are ideal candidates for this purpose. These devices are intrinsically solar blind, in which no additional filters are needed, they have low noise, 7 and fast response times. 8 The lack of high internal gain has been the major limitation for the usage of AlGaN photodetectors for applications that require high sensitivity detectors. There have been several theoretical research work that examined the avalanche effect in GaN and AlGaN-based structures. 9-11 Experimental work on both GaN ͑Refs. 12-18͒ and AlGaNbased ͑Refs. 4, 19, and 20͒ avalanche photodiodes ͑APDs͒ were also reported. However, reproducible high gain in AlGaN-based APDs is still a major limitation. In this letter, we report the realization of solar-blind AlGaN-based avalanche photodetectors with reproducible high avalanche gain.The epitaxial structure of the avalanche photodetector is designed for solar-blind operation w...

Design, fabrication, and characterization of high-performance Al x Ga 1 x N-based photodetectors for solar-blind applications are reported. Al x Ga 1 x N heterostructures were designed for Schottky, p-in , and metal-semiconductor-metal (MSM) photodiodes. The solar-blind photodiode samples were fabricated using a microwave compatible fabrication process. The resulting devices exhibited extremely low dark currents. Below 3 fA, leakage currents at 6-V reverse bias were measured on p-in samples. The excellent current-voltage (-) characteristics led to a detectivity performance of 4.9 10 14 cmHz 1 2 W 1. The MSM devices exhibited photoconductive gain, while Schottky and p-in samples displayed 0.09 and 0.11 A/W peak responsivity values at 267 and 261 nm, respectively. A visible rejection of 2 10 4 was achieved with Schottky samples. High-speed measurements at 267 nm resulted in fast pulse responses with greater than gigahertz bandwidths. The fastest devices were MSM photodiodes with a maximum 3-dB bandwidth of 5.4 GHz.

Design, structure growth, fabrication, and characterization of high performance AlGaN-based metal-semiconductor-metal (MSM) photodetectors (PD) are reported. By incorporating AlN nucleation and buffer layers, the leakage current density of GaN MSM PD was reduced to 1.96 Â 10 À10 A/cm 2 at a 50 V bias, which is four orders of magnitude lower compared to control devices. A 229 nm cutoff wavelength, a peak responsivity of 0.53 A/W at 222 nm, and seven orders of magnitude visible rejection was obtained from Al 0.75 Ga 0.25 N MSM PD. Two-color monolithic AlGaN MSM PD with excellent dark current characteristics were demonstrated, where both detectors reject the other detector spectral band with more than three orders of magnitude. High-speed measurements of Al 0.38 Ga 0.62 N MSM PD resulted in fast responses with greater than gigahertz bandwidths, where the fastest devices had a 3-dB bandwidth of 5.4 GHz.

Cataloged from PDF version of article.Al0.38Ga0.62N/GaN heterojunction solar-blind Schottky photodetectors with low dark current, high responsivity, and fast pulse\ud response were demonstrated. A five-step microwave compatible fabrication process was utilized to fabricate the devices. The solarblind\ud detectors displayed extremely low dark current values: 30lm diameter devices exhibited leakage current below 3 fA under\ud reverse bias up to 12V. True solar-blind operation was ensured with a sharp cut-off around 266 nm. Peak responsivity of\ud 147mA/W was measured at 256 nm under 20 V reverse bias. A visible rejection more than 4 orders of magnitude was achieved.\ud The thermally-limited detectivity of the devices was calculated as 1.8 · 1013 cmHz1/2W 1\ud . Temporal pulse response measurements\ud of the solar-blind detectors resulted in fast pulses with high 3-dB bandwidths. The best devices had 53 ps pulse-width and 4.1GHz\ud bandwidth. A bandwidth-efficiency product of 2.9GHz was achieved with the AlGaN Schottky photodiodes. (C) 2004 Elsevier Ltd. All rights reserve