A simple yet comprehensive unified physical model of the donor layer electrons in delta-doped and uniformly doped HEMT's

The trapped and free electrons in the donor layer of a high electron mobility transistor (HEMT) play an important role in limiting the current modulation efficiency and the current-gain cutoff frequency of the device. This paper presents a simple model, which closely tracks accurate but complex numerical calculations of the concentration and capacitance of these electrons as a function of the gate voltage. The model is comprehensive in the sense that it captures the effects of all device parameters including temperature on trapped as well as free electrons, and encompasses both uniformly doped and delta-doped HEMT's. A simple power law charge voltage function, which is both differentiable and integrable, is shown to adequately represent the behavior of the two types of donor layer electrons in both the HEMT's. The model is useful in the design and simulation of ac performance of HEMT devices and circuits. Together with the n/sub s/-V/sub G/ model proposed recently by the authors of this paper, it gives a complete yet simple analytical picture of all the charges of significance in a general HEMT.