TERM PAPER (EE 311) AlGaN/ GaN HEMT: AN OVERVIEW OF DEVICE OPERATI ON, ITS ADVANTAGES AND LIMITATIONS Ankita Agrawal (Y8096) Kamal Sahni (Y8232) Kanav Gupta (Y8234) Puneet Agr awal (Y8375) Subhali Subhechha (Y8508) Tar un Kr .Bar anwal (Y8529) ABSTRACT: HEMTs are the fastest transistors currently available, as commercial models can already amplify signals of 40 GHz. The unique properties of the HEMT is a result of its use of band gap engineering to create a 2 dimensional electron gas, which is confined into a pure region of the crystal, and can move with the full mobility of the intrinsic material . The HEMT operates much like a normal depletion mode MOSFET, only much faster . The fabrication process is very similar to MESFET one. Conventional flow process includes following stages: growth of buffer layer, alternating layers, active channel, spacer layer, and donor layer. Use of Gallium Nitride (GaN) as a main element in a device allows overall high increase of transistor performance. The characteristics of HEMTs make them ideal for use in high-frequency amplifiers, and hence HEMTs find their way into use in satellite communications, point-to-point microwave communications, and for the electrical components of optical devices. THEORY AND OPERATION: Like JFET and the MESFET, HEMT devices also use the electric field to control the flow of current through the device. The design goal of the HEMT is to create a device that will work at high frequencies, and as a consequence, such a device needs high electron mobility and velocity to keep up with such signals. The HEMT is characterized by its creation of a 2 dimensional electron gas (2DEG). A 2DEG is an effect dictated by the principles of quantum mechanics and a uniquely shaped potential well. A triangular potential well is created. Electrons tunnel into it, but cannot get out. In the well, the electrons obey their wave properties (recalling that everything is both a particle and a wave at the same time), and end up in the part of the well corresponding to the first half-wavelength of the electron, called the first energy sub band. They cannot go any deeper into the potential well because quantum mechanics states that they have a zero probability of taking up a space smaller than their half-wavelength. Of course, this channel only covers one of the dimensions, in this case the thickness of the device. The electrons are free to form a sheet in the other two dimensions (length and width of the device), and since the motion of the charges in the sheet is random, like a gas (especially like the electron gas that is considered to be in metals) we arrive at the term two-dimensional electron gas. Figure 1: Heterojunction Cross Section The typical form of the HEMT is a device containing interfaces between N + Aluminium gallium arsenide (AlGaAs), undoped AlGaAs, and undoped Gallium arsenide (GaAs), although The image cannot be displayed. Your computer may not have enough memory to open the image, or the image may have been corrupted. Restart your computer, and then open the file again. If the red x still appears, you may have to delete the image and then insert it again.