High Quantum Efficiency AlGaN/GaN Solar-Blind Photodetectors Grown by Metalorganic Chemical Vapor Deposition

Abstract

We report the growth, fabrication and characterization of high-quality AlGaN/GaN solar-blind p-i-n and MSM photodetectors by low-pressure metalorganic chemical vapor deposition (MOCVD). The epitaxial layers were grown on double-polished c-plane (0001) sapphire substrates to allow for back-side illumination. The p-i-n photodiode structures typically consist of a 0.7 mm thick Al 0.58 Ga 0.42 N "window" layer, graded to a 0.2 mm thick Al 0.47 Ga 0.53 N n layer, a 0.15 mm thick Al 0.39 Ga 0.61 N i layer, a 0.2 mm thick Al 0.47 Ga 0.53 N p layer, and capped with a 25 nm GaN : Mg contact layer. At a 0 V bias, the processed p-i-n devices exhibit a solar-blind photoresponse having a maximum responsivity of 0.058 A/W at 279 nm, corresponding to an external quantum efficiency of $26%, uncorrected for reflections, etc. The MSM devices typically consist of an AlGaN x $ 0.58 window layer, and an undoped AlGaN x $ 0.44 absorbing layer. The MSMs exhibit an external quantum efficiency as high as $47% at a bias of 15 V with a peak response at 262 nm.Introduction Photodetectors operating in the wavelength range between 250 and 300 nm, referred to as the solar-blind regime, can be used for applications such as missile detection and tracking and for biological agent and chemical detection. The III-nitride material system is ideal for these detectors, as they can be designed to have a cutoff wavelength below 300 nm. The metal-semiconductor-metal (MSM) device is well suited for this application, as it is relatively simple to fabricate and its low capacitance can result in a fast response time. Advances in material growth have resulted in high aluminum composition and crack-free AlGaN heterostructures for use as solarblind p-i-n photodetectors [1]. The p-i-n device has the advantage of operating at zero to low bias, eliminating the requirement for a bulky power supply. We report the growth, fabrication and characterization of high-quality AlGaN/GaN heteroepitaxial back-illuminated solar-blind p-i-n and MSM photodetectors with high external quantum efficiencies.

High bandwidth-efficiency solar-blind AlGaN Schottky photodiodes with low dark current

“…Since the first demonstration of solar-blind AlGaN photoconductors [4,5], research on high Al-content Al x Ga 1Àx N solar-blind detectors resulted in high-performance devices. AlGaN-based solar-blind photodetectors with very low leakage and noise levels [6,7], high responsivity [8,9], high detectivity [10,11], and fast pulse response [12] have been reported.…”

III–Nitride UV Devices

“…Solar-blind AlGaN-based MSM detectors have also been reported with quantum efficiencies up to 47% at 262 nm. [81][82][83][84] Recently, an MSM detector based on magnetron sputtered AlN with a high internal gain due to carrier trapping has also been demonstrated. 85) Various configurations of visible-blind GaN [86][87][88][89][90][91][92] and solar-blind AlGaN [93][94][95][96] p-n junction based photodetectors have been reported by many groups.…”

High-Performance Solar-Blind Photodetectors Based on Al<tex>$_rm x$</tex>Ga<tex>$_1-rm x$</tex>N Heterostructures

“…Schottky [18]- [23], p-i-n [24]- [38], MSM [39]- [44], and p-n junction [45] types of photodiodes with excellent detection characteristics were reported. Very low dark currents at the femtoampere level [22], [35], [36], [39] and high solar-blind responsivity performance [29], [33], [37] resulted in extremely high detectivity values which could not be achieved with conventional narrow bandgap semiconductor-based detectors. High visible rejection of more than six orders of magnitude [25], [45] and low cutoff wavelengths down to 225 nm [25] were also successfully reported.…”