The development of systems using microwaves for military telecommunications and consumer, requires discrete components and power that can operate at high frequencies. It is efficient components for operating systems such as high electron mobility transistor (HEMT). The potential of transistors HEMTs based heterostructure AlGaN / GaN high interest to the international scientific community and are certainly the most currently studied worldwide. They have emerged as attractive candidates for applications in high voltage, high frequency to microwave power. By the spontaneous and piezoelectric polarization, they have the facility to produce a two-dimensional electron gas (2DEG) at the interface with a high concentration without doping intensional. The market for power components based on this material is booming for many applications. In this article we studied some properties of nitride materials existing in the structure for a better functioning of the component, it is necessary to have a physical simulation model for describing the heterojunction AlGaN / GaN, and the fundamental principles of electrical operation a HEMT transistor. In this model, this electron mobility 2DEG depending on the gate voltage in the transistor channel and the Al concentration.