Preetam Jain Int. Journal of Engineering Research and Applications www.ijera.com ISSN : 2248-9622, Vol. 5, Issue 3, ( Part -3) March 2015, pp.111-116 www.ijera.com 111 | Page Three Dimensional Modelling of MISFET Preetam Jain, Lochan Jolly ME Student Department of Electronics & Telecommunication, TCET Mumbai Professor Department of Electronics & Telecommunication, TCET Mumbai Abstract— Recent research shows the tremendous potential for the development of optical devices viz. photo-detector, optical sources, connectors and applications etc. This is mainly because of the success of optical communication in the recent for gigabit transmission and is intended for terabits transmission in future. In this paper, mathematical model for the optical dependence of I-V, C-V characteristics of MISFET structure (to be used as photo-detector) is reported. Model is based on solution of Poisson‟s and current c ontinuity equation. Proposed structure of MISFET includes, In 0.53 Ga 0.47 As used as substrate material and InP as insulator. Light is made to incident perpendicular to the surface. Drain current can be controlled optically by means of varying light intensity of incident radiation. There is significant effect of intensity modulation on IV and CV characteristics of MISFET. As a result of intensity modulation, drain current increases significantly in presence of illumination mainly due to change in carrier concentration of channel results from photo-generated carriers. Simulation of mathematical model is carried out in MATLAB. Keywords—MISFET; Modeling; Optical I. INTRODUCTION Ever since ancient times, people had a principle need to communicate with one another. This need created interests in devicing communication system for sending messages from one distant place to another. Optical communication methods were of special interest among the many systems. The basic function of an optical fiber link is to transport a signal from communication equipment at one location to corresponding equipment at another location with a high degree of reliability and accuracy.The main constituents of an optical fiber communication link are transmitter consisting of optical source, an optical cable and a receiver consisting of a photo-detector. Photo-detector is the first element of the photo receiver circuit which interprets the information contained in the optical signal.They demodulate the optical signal that are subsequently amplified and processed to obtain the actual information signal. For such applications, photo-detectors must have high sensitivity, high responsivity and minimum noise. In addition, the photo-detectors should be compact in size, use low biasing voltage and current, reliable under operating condition, and preferably integrated circuit compatible[1,2]. Field effect transistors (FET) devices are sensitive to light, having high package density and are suitable for microwave applications. Lots of efforts are carried out in the development of microwave transistors from III-V compound semiconductor material systems [4]. Presently the GaAs Schottky- gate FET (MESFET) is the only such device commercially available. Irrespective of remarkable microwave gain and noise performance, this device suffers from the limitations of a restricted range of enhancement operations. Schottky contact gate structure of GaAs MESFET produces large gate leakage current, when used on InP and InGaAs. MIS structure offers very low leakage current and reduces gate capacitances. In x Ga 1-x As is a promising material for advanced optoelectronic devices. In 0.53 Ga 0.47 As is a good substrate for such circuits. In 0.53 Ga 0.47 As lattice matched to semi-insulating InP has higher low field mobility, high drift mobility and peak electron velocity [5,6]. Therefore, InGaAs MISFETs have potential for better microwave performance. In the paper an optically gated Metal-Insulator-Semi conductor Field-Effect-Transistor (MISFET) structure has been characterized theoretically to examine its potential as an photo-detector in 1 to 1.6 μm wavelength region. Numerical calculations have been carried out to determine the I-V characteristics of the device in various illuminated conditions. Quantum efficiency of MISFET is also calculated. II. THEORY The schematic structure of the MISFET under consideration is shown in fig.1 for the case of a n- channel formed on a p-type substrate. The n + source and drain regions can be formed by using ion- implantation into the relatively lightly doped p-type substrate. A thin semi-insulating InP (InP:Fe) layer separates the semi-transparent metal gate from the InGaAs surface. The thickness of the device is considered along the x-axis, length along the y-axis and width along the z-axis. The optical radiation is incident in the x-direction and drain to source current flows in y direction. The doping concentration of p- RESEARCH ARTICLE OPEN ACCESS