High Sensitivity Photodetector Using Si/Ge/GaAs Metal Semiconductor Field Effect Transistor (MESFET) Rajni Gautam 1 , Manoj Saxena 2 , R.S.Gupta 3 , and Mridula Gupta 1 1 SDRL, Deptt. Of Elect. Sci., University Of Delhi, South Campus, Benito Juarez Road, New Delhi -110021, India 2 Department Of Electronics, Deen Dayal Upadhyaya college, University Of Delhi, Karampura, New Delhi -110015, India 3 Deptt. Of ECE,Maharaja Agrasen Institute Of Technology, Sector 22, Rohini, Delhi- 110086, India Email: rajni7986@gmail.com, saxena_manoj77@yahoo.co.in, rsgu@bol.net.in, mridula@south.du.ac.in Abstract. The paper presents the comparative study of MESFET as photodetector for three different channel materials: Si, Ge and GaAs using ATLAS 3D device simulator. Common semi-insulating substrate i.e. sapphire is used for all the three MESFETs. Effect of illumination on the performance of the device has been studied in detail in terms of ratio of dark current to current under illumination, threshold voltage shift and enhanced drain current. Keywords: ATLAS-3D, MESFET, photodetector, sensitivity PACS: 85.30.Tv, 85.60.Gz INTRODUCTION The Optically controlled MESFET (OPFET) has drawn considerable attention for last two decades for the designing of various optically controlled monolithic microwave integrated circuits (MMIC’s) and optoelectronic integrated circuits (OEIC’s) [1]. The dc and microwave characteristics of such a device can be controlled precisely by applying optical radiation on it. In optical communication systems, OPFET photodetectors [2] are supposed to be very promising. Recent efforts to develop photodetectors have centered around high data rate applications where the main focus of device structure and design has been to achieve high quantum efficiency and lower dark current. Two dimensional image sensors require small monolithic photodetectors with high sensitivity. Another application of small photodetector is optical on-chip interconnection in which high sensitivity detector is used as a receiver. Photodetectors can be fabricated from a broad range of materials. The material selection is based on a number of factors including optical properties (refractive index, absorption), electrical properties (mobility and conductivity), stability and process compabilities. Depending upon the absorption at the desired wavelength in the UV, visible and near IR regions of spectrum we have simulated MESFET based photodetector for three channel materials: Si, Ge and GaAs. Silicon technology [3],[4] is all pervasive and underpins the IT revolution that is now reshaping society. The technology keeps improving year on year as chip sizes are being continually reduced and transistor speed increases. In order to achieve higher detection efficiency, absoption at wider range of frequencies new channel materials are being used. Ge [5]-[7] has particularly become of great interest as a channel material for IR detection. GaAs has many advantages over Silicon such as higher electron mobility, shorter transit time, higher rresistivity, lower thermal conductance and is commonly used for optically controlled MESFET devices [8]-[9]. In this paper, we have studied the performance of MESFET based photodetector for three different channel materials: Si, Ge and GaAs using ATLAS 3D device simulator [10]. Common semi-insulating substrate i.e. sapphire is used for all the three MESFETs. The three photodetectors have been optimized to have same threshold voltage (i.e. V th = -0.18 V) under dark so as to compare their performance in terms of ratio of drain current under illumination to the drain current under dark conditions i.e. I illum /I dark at different biasing conditions. The impact of variation of intensity of incident radiation and its wavelength has also been studied in detail through extensive simulations. DEVICE STRUCTURE The schematic structure of a MESFET under illumination is shown in Fig. 1. Optics: Phenomena, Materials, Devices, and Characterization AIP Conf. Proc. 1391, 232-234 (2011); doi: 10.1063/1.3646835 © 2011 American Institute of Physics 978-0-7354-0960-6/$30.00 232 Downloaded 01 Nov 2011 to 202.141.127.2. Redistribution subject to AIP license or copyright; see http://proceedings.aip.org/about/rights_permissions