A 2-D simulation of off-state breakdown voltage (VBD) for AlGaN/GaN high electron mobility transistors (HEMTs) with multi field-plates (FPs) is presented in this paper. The effect of geometrical variables of FP and insulator layer on electric field distribution and VBD are investigated systematically. The FPs can modulate the potential lines and distribution of an electric field, and the insulator layer would influence the modulation effect of FPs. In addition, we designed a structure of HEMT which simultaneously contains gate FP, source FP and drain FP. It is found that the VBD of AlGaN/GaN HEMTs can be improved greatly with the corporation of gate FP, source FP and drain FP. We achieved the highest VBD in the HEMT contained with three FPs by optimizing the structural parameters including length of FPs, thickness of FPs, and insulator layer. For HEMT with three FPs, FP-S alleviates the concentration of the electric field more effectively. When the length of the source FP is 24 μm and the insulator thickness between the FP-S and the AlGaN surface is 1950 nm, corresponding to the average electric field of about 3 MV/cm at the channel, VBD reaches 2200 V. More importantly, the 2D simulation model is based on a real HMET device and will provide guidance for the design of a practical device.

A comprehensive model for 2DEG characteristics of InxAl1−xN/AlN/GaN heterostructure has been presented, taking both polarization and bulk ionized charge into account. Investigations on the 2DEG density and electron distribution across the heterostructure have been carried out using solutions of coupled 1-D Schrödinger-Poisson equations solved by an improved iterative scheme. The proposed model extends a previous approach allowing for estimating the quantum mechanical effect for a generic InAlN/GaN-based HEMT within the range of the Hartree approximation. A critical AlN thickness (~2.28 nm) is predicted when considering the 2DEG density in dependence on a lattice matched In0.17Al0.83N thickness. The obtained results present in this work provide a guideline for the experimental observation of the subband structure of InAlN/GaN heterostructure and may be used as a design tool for the optimization of that epilayer structure.

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