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Physics based threshold voltage (V th ) models for Al x GaN 1-x /AlN/GaN and double channel (DH-Al x GaN 1-X ) HEMT devices are presented. Based on the concept that donor like surface states located on the AlGaN top are the source of electrons in the 2DEG, analytical Schottky barrier height (ϕ b ) expression is derived and used in the development of the threshold voltage models. The calculated V th values for sample AlGaN/AlN/GaN and DH-Al x GaN 1-X HEMT devices are consistent with the values extracted from published experimental data. Moreover, the V th models are incorporated in a recently proposed charge based I-V model for GaN HEMTs and DC characteristics of the devices under test are simulated. The model predictions are strongly correlated with experimental data in both the output and transfer characteristics cases over a full range of biasing conditions.

In this paper, DC characteristics of an AlGaN/GaN on sapphire high-electron mobility transistor (HEMT) are measured, numerically simulated, and modelled accounting for selfheating effects (SHEs), with the main electrical parameters being extracted. Decomposing the transistor thermal resistance into the buffer and substrate components, our study can be easily extended to other substrate materials. Thus, sapphire is substituted with silicon, molybdenum, and SiC, which reduce current-collapse due to SHEs thanks to their considerably higher thermal conductivity, which improves transistor performance. Furthermore, we implement a compact model available for AlGaN/GaN HEMTs, incorporating the temperature dependence of extrinsic source/drain ohmic resistances, which are numerically evaluated for the different substrates.

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