A simple yet comprehensive unified physical model of the 2d electron gas in deltadoped and uniformly doped high electron mobility transistors shreepad karmalkar

This paper presents a new approach to model the 2DEG concentration (ns) versus gate voltage (VG) behavior and the equilibrium 2DEG concentration (ns0) in a HEMT. The approach results in a model which is "comprehensive" in the following sense. It is valid for both deltadoped and uniformly doped HEMT's. It captures all the three nsVGnonlinearities (subthreshold gradual pinchoff and gradual saturation) and the effects of all the device parameters including temperature in relation expressing ns as an explicit closedform integrable function of VG having continuous first derivatives; thus the function readily yields a device currentvoltage/capacitancevoltage (IV/CV) model which can be incorporated in softwares meant for simulation of circuits particularly of the analog variety. The simple model is shown to predict the results of complex numerical calculations and experiments. The closedform ns0 expression of the model is the first of its kind reported for deltadoped HEMT's and reveals an interesting feature unexposed by earlier ns0 models: the reciprocal of ns0 in both deltadoped and uniformly doped devices decreases linearly with reduction in spacer width and saturates at low spacer widths in some deltadoped devices. It is shown that the measured ns0 in deltadoped devices is predicted correctly if the electrons in the Vshaped well are assumed to be trapped at the donor sites rather than to be filling the conduction subbands. © 2000 IEEE.