Study On AlGaN/GaN MOS-HEMT's Characteristics

Recent progress in AlGaN/GaN Heterostructure Field Effect Transistors (HFETs) has demonstrated that they are key devices for high-power microwave application. However, many questions related to the material quality such as defect states and trapping effects in a heterostructure and following device performance reliability are still open. Passivated HFETs with a gate insulator, metal-oxide semiconductor (MOS)HFETs are therefore under systematic studies because they lead to smaller gate leakage current and allow the suppression of surface state defects and thus increase in the output power. On the other hand, high band gap of GaN opens an application area for devices they can operate at elevated temperatures.In this paper, a Metal Oxide Semiconductor High-Electron-Mobility Transistor (MOS-HEMT) with Atomic Layer Deposition (ALD) 10nm Al2O3 gate dielectric is manufactured. The superiorities on saturation current and leakage current of the novel MOS-HEMT devices are verified through room temperature characteristics contrast of the MOS-HEMT and traditional MES-HEMT devices. This paper also illustrates the statistics analysis of the device feature variation at 30-180℃range, which shows the distinction of degradation degree by temperature between the two kinds of devices. Thus, the conclusion that the device saturation currents and the transconductance degradations are mainly caused by transport characteristic degradation can be summarized. Dependence of capaticance on temperature shows difference in the two kinds of devices, which is supposed that, the number of traps in the surface between Al2O3 gate and AlGaN in the MOS structure is smaller than that in the Schottky contact. In order to quantitatively analyze an influence of traps on performance of MES-HEMT and MOS-HEMT, the curve of temperature dependence of the threshold voltage is fitted. All those statistics and analysis results witnesses the significant role played by the reduced surface state in the surface of the AlGaN in optimizing the characteristics of the device.