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In this paper, the performance difference of AlGaN/GaN high-electron mobility transistors (HEMTs) with same epitaxial structure fabricated silicon carbide (SiC) and transferred to diamond substrate is examined based on the surface-potential (SP) model. The thermal resistances of these devices are extracted through finite element method (FEM) thermal analysis. Results show that GaN-ondiamond device has a lower thermal resistance than conventional GaN-on-SiC device, which demonstrates the thermal performance improvement of GaN-on-Diamond technology. By embedding thermal characteristic into carrier mobility in the conventional SP model, the effectiveness of model is validated through good agreement between simulation and measurements of DC and RF performance. Additionally, large-signal performance (output power P out , power added efficiency P AE and Gain) on these two similar devices are compared under identical bias and temperature conditions based on the improved SP model, making this work be effective for improving the process of GaN-on-Diamond HEMTs. The excellent performance of GaN materials including wide bandgap, high thermal conductivity, high electron saturation drift velocity makes it very suitable for the development of highfrequency, high-power microwave and millimeter-wave device and circuit applications.1,2 SiC material is presently a major choice to implement high-performance GaN HEMT due to its high thermal conductivity that is an order of magnitude greater than that of other materials such as sapphire. However, the heat dissipation issue appears more and more prominent with the development to direction of smaller size, greater output power and higher frequency. Therefore, to solve the degradation of device performance and reliability caused by heat dissipation, it is of utmost importance to reduce thermal resistance to get good thermal management. [3][4][5] Recently, GaN HEMT devices fabricated on diamond substrate (GaN-on-diamond) have been developed 6,7 due to its high thermal conductivity (2000 W/m · K) that is three to four times that of SiC. The application of diamond substrate can significantly reduce the temperature rise of device, which is expected to solve the performance degeneration under conditions of high bias and power drive. [8][9][10] Accurate device model, especially physical model, is essential for predicting device performance and guiding process development. This paper discusses the comparison result of performance between GaN HEMTs fabricated on SiC and diamond substrates based on the SP model. The paper is organized as follows. In Device structure and fabrication section, the structure and fabrication process of GaN-onDiamond HEMTs are described in detail. Then the 3D FEM model and SP model are described briefly in Thermal analysis setup and results section and SP model description for following performance verification and discussion in RF Performance verification section. Finally, Conclusion section is the conclusion. Device Structure and FabricationThe cross-section view o...

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AlGaN/GaN high-electron-mobility transistor (HEMT) structures with two and three Al-containing step-graded AlGaN buffer layers (BLs) were grown on silicon (111) substrates by metal organic chemical vapor deposition. Considerable tensile stress was observed in the GaN grown with only two 0.8 µm AlGaN BLs, while a large in-plane compression in GaN grown with three 2.3 µm AlGaN BLs. The reverse gate leakage current in the HEMT with three AlGaN BLs was approximately 0.1 µA/mm, which was more than one order of magnitude smaller than that for the HEMT with two AlGaN BLs. A three-terminal off-state breakdown voltage of 265 V and a vertical gate-to-substrate breakdown voltage of 510 V were obtained in the HEMT with three AlGaN BLs. Detailed analysis was performed on the basis of the structural properties of AlGaN/GaN heterostructures.