ARTICLE Copyright © 2013 by American Scientific Publishers All rights reserved. Printed in the United States of America Energy and Environment Focus Vol. 2, pp. 1–5, 2013 (www.aspbs.com/efocus) Electrical and Optical Transient Behavior of n-GaN Metal-Semiconductor-Metal (MSM) Photodetector Z. Muhammad * , T. Munir, and S. Naseem Microelectronics Division/Center of Excellence in Solid State Physics, University of the Punjab, Lahore-54590, Pakistan ABSTRACT The low dark current and fast response speeds are the current challenges of MSM photodetector. The perfor- mance of MSM structure is strongly influenced by metallization and temperature gradient. In this paper, various high work function Schottky metal Pt, Pd and Ni on n-GaN MSM photodetector have been simulated under various temperatures from 300 K∼500 K to optimize electrical (I –V ) and transient behavior. It was found that metal with highest work function Pt shows lowest dark current (6.4 × 10 -13 A) at 20 V reverse bias compared to Pd and Ni at room temperature. The e-current density at metal/semiconductor interface enlarges deple- tion width which produces low dark current for Pt Schottky metal. For optical transient analysis, Pt metal on n-GaN shows slightly faster response (25 ps) than Pd and Ni metals at room temperature. The dark current and optical response time increases with increase in room temperature due to free carrier generation across metal/semiconductor interface. KEYWORDS: Dark Current, Response Speed, MSM. 1. INTRODUCTION The wide band gap GaN and related materials have extensively investigated in recent years due to their excit- ing applications in high-temperature and high-power elec- tronic devices. GaN because of its high eligibility to work in the UV visible blind region that ranges from 400 nm to 300 nm wavelength are extensively used in UV photodetectors. Such photodetectors are used as bio- logical and chemical sensors, flame sensors, spatial opti- cal communications, emitter calibration and UV imaging etc. 1 GaN based UV photodetector shows advantages with other semiconductor material due to high robustness, high absorption due to direct and wide bandgap, high chemical and radiation resistant due to high bond strength, thermally stable at higher temperature, high breakdown field and sat- uration velocity, suited for high power and high frequency transistors for microwave application. 2 Different designs previously reported, based on GaN material are p–n junctions, p–i–n type diodes, Schottky diodes, metal-semiconductor-metal (MSM) photodiodes and heterojunction structures. Among these devices, there is a keen interest in developing photodetectors in the form of metal-semiconductor-metal (MSM) structure due to rea- sons like fabrication simplicity, low dark currents, lower ∗ Author to whom correspondence should be addressed. Email: zeecom84@yahoo.com Received: 15 April 2013 Accepted: 3 July 2013 intrinsic capacitance, large active area for photodetection, fast response, large bandwidth, low noise, and the suitabil- ity for the monolithic integration of an optical receiver. 3 The lowest dark current and fast response speed are the current challenges of n-GaN MSM photodetector. In order to have low dark current and high speed, metallization on GaN is a crucial factor of the MSM structure, since it strongly influences the performance of a device. 4 The previously reported electrical I–V characteristic 5–7 of GaN MSM photodetectors shows that dark current is much higher due to the low barrier heights between metal and semiconductor. To produce high-performance MSM UV photodiodes, it is important to achieve a large Schottky barrier height at the metal–semiconductor interface that leads to lowdark current and high breakdown voltage which could result in improving responsivity and photocur- rent. To achieve a large Schottky barrier height on GaN, one can choose metals with high-work functions. 8 How- ever, many of the high-work function metals are not stable at high temperatures. Thermal study is also very important to see how the device performs at severe conditions. The transient response has been mostly studied for GaAs based MSM photodetectors. 9–11 However, response time has been studied 12 of submicron MSM UV photodiodes on GaN and found that the response speed retards due to space- charge screening effect. Similarly, the transient response has been studied 13 for GaN based MSM photodetectors by varying epilayer thickness and contact spacing. In the present study, we firstly reported the analysis of the optical Energy Environ. Focus 2013, Vol. 2, No. 3 2326-3040/2013/2/001/005 doi:10.1166/eef.2013.1048 1