Light intensity dependence of photocurrent gain in single-crystal diamond detectors

Abstract

The authors report on the photocurrent gain in a diamond photodetector that has two nonohmic contacts connected back-to-back. This photocurrent gain strongly depends on both the deep-ultraviolet ͑DUV͒ light intensity and the applied voltage. In addition, the gain is accompanied by a slow response. The gain is observed to originate from a metal/diamond interface trap center. Numerical analysis discloses that the photocurrentvoltage characteristics follow thermionic-field emission tunneling at low DUV light intensity and fieldemission tunneling at high DUV light intensity. The deep traps are thought to produce a thin interface barrier layer at the metal/diamond interface under DUV illumination, which is responsible for the tunneling processes.The interest in the utilization of diamond for deepultraviolet ͑DUV͒ detection has been triggered due to its extreme properties and the progress in the development of high-quality single-crystal diamond layers. 1-5 An important issue for practical devices is to achieve high responsivity or photocurrent gain while maintaining a fast response time. The high responsivity is important for weak signal detection such as flame or chemical sensing and DUV imaging with reduced pixel size.One strategy to generate photocurrent gain is to utilize quantum well structures or to introduce deep bulk defects. 6,7 As for diamond photodetectors, the incorporation of boron in the homoepitaxial layer can greatly improve the responsivity. In that case, the boron in the epilayer and the nitrogen in the substrate were dominant factors in the photoresponse behavior due to the formation of a p-n junction at the interface. A huge photocurrent gain was obtained when the boron content in the epilayer was relatively high, which was explained in terms of deeply trapped carriers by the ionized nitrogen in the substrate. 7 Since such a gain mechanism is controlled by the carrier transport in the epilayer, the metal contact to the diamond layer must be the ohmic type or Schottky type in the forward bias mode. In fact, no photocurrent gain was observed in the devices in our previous work if the metal/ diamond contacts were the blocking type. 8 In this work, we report that photocurrent gain can be generated as the DUV light intensity increases in a homoepitaxial diamond photodetector with two nonohmic contacts connected back-toback. The transient photocurrent behavior at different biases and the temperature effect on the photocurrent gain are investigated to understand the gain mechanism.The diamond layer was grown on a high-pressure hightemperature type-Ib ͑100͒ substrate using a microwave plasma-enhanced chemical vapor deposition reactor, which makes it possible to deposit a diamond epilayer at a much higher speed than our previous system. Hydrogen and methane gases were fed for diamond growth. In this apparatus, a higher methane concentration with a CH 4 / H 2 flow ratio of 2% was applied to achieve a higher growth rate. The substrate was heated to 1000-1090°C by high power plasma during growth. The total pre...

Broad spectral response photodetector based on individual tin-doped CdS nanowire

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Large‐Area Bilayer ReS2 Film/Multilayer ReS2 Flakes Synthesized by Chemical Vapor Deposition for High Performance Photodetectors

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Electrical Transport and High‐Performance Photoconductivity in Individual ZrS2 Nanobelts

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