International Conference and Workshop on Emerging Trends in Technology (ICWET 2010) – TCET, Mumbai, India 923 Impact of Concentration Dependent Carrier Mobility & Lifetime on Opaque Gate Controlled MESFET R B Lohani Dept of Electronics and Telecommunication Engineering Goa College of Engineering (Govt of Goa) Farmagudi, Ponda Goa, India +91-8322336341 rblohani@gec.ac.in J Gaitonde Dept of Electronics and Telecommunication Engineering Goa College of Engineering (Govt of Goa) Farmagudi, Ponda Goa, India +91-9420690070 vupgaitonde@rediffmail.com ABSTRACT Optically controlled MESFET are useful device for optical communication and as photodetectors. Mobility and life time of carriers are strongly function of impurity concentration. In this paper the IV characteristerstics of an opaque gate Optically controlled MESFET is presented at the low impedance state of the device. Considering concentration dependent carrier mobility and life time of carrier. The result indicate that the concentration dependent mo Mobility and life time have strong effect on optical controlled opaque gate MESFET characteristics. Categories and Subject Descriptors B.7.1 [Integrated Circuits]: Advanced Technology General Terms Measurement, Performance, Experimentation, Standardization, Theory, Legal Aspects, Verification Keywords Opaque Gate MESFET, Optical controlled MESFET, GaAs Devices, High Speed Optical Devices, Photodetectors, Dual Memory Device in computers, mobility and lifetime 1. INTRODUCTION In recent years experimental studies indicates that electrical characteristics are very responsive to the light of the visible and infrared frequencies. These prompted optically controlled MESFET, from GaAs, with transparent or semitransparent schottky gate. It has been indicated that the optical controlled MESFET can be used as a dual memory device in computers wth one gate been real where the voltages apply and the other gate virtual (where the radiation is allowed to fall)[5]. Experimental and theoretical work has been published on optical effects in GaAs MESFETs[1-4] which shows enhancement in device current and transconductance. The result is due to channel conductivity modulation and photo voltaic effect within the device. However the accurate device modeling, we have considered different transport parameters in appropriate form. In the present work, we have considered two parameters mobility and lifetime of carrier of an opaque gate, optically controlled MESFET where radiation is absorbed through the spacing of source and gate and drain. And consider them as function of active layer. It is particularly important because the doping concentration in the active region is significantly high(~>10 17 /cm) in GaAs MESFET. For the closed channel form solution, in the active layer is assumed to be constant. 2. Theory The schematic structure of optically controlled opaque gate GaAs MESFET is same as considered in[4]. The mobility of electron is considered to have concentration dependence as given in equation 1 below[6]. μ n =μ on [1+(N D /N Dr ) 0.5 ] -1 (1) where μ on is the mobility independent of doping concentration. N D is the donor concentration in the active region and N Dr is a reference concentration and vary from material to material. For GaAs, N Dr is taken as 10 17 /cc. The minority carrier lifetime has the concentration dependence given in equation 2 below[1]. n,p = n,po [1+(N D /N Dr )] -1 (2) where n,po is the doping independent minority carrier life time. po =10 -8 sec and no =10 -6sec . The excess carriers are solved using continuity equations for holes and electronics. Taking into consideration taking into consideration the photo generation and both surface and bulk recognition the total channel charge is given Q t =Q 2ch +Q 3dep +Q i (3) Where Q 2ch is that in the channel, Q 3dep is the charge generated in the channel substrate depletion and Q i is due to impurities in the channel. As the gate is opaque no charge is generated in the gate depletion region. The current is calculated for low impedance state of the optically controlled opaque gate MESFET using the relation given in equation 4. V DS Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. To copy otherwise, or republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee. ICWET’10, February 26–27, 2010, Mumbai, Maharashtra, India. Copyright 2010 ACM 978-1-60558-812-4…$10.00.