Effect of GaN Buffer Layer Growth Pressure on the Device Characteristics of AlGaN/GaN High-Electron-Mobility Transistors on Si

Abstract

AlGaN/GaN High-electron-mobility transistor (HEMT) structures on silicon were grown by Metalorganic chemical vapor deposition (MOCVD) with various growth pressures during the growth of 1.5 µm thick GaN. The grown samples were characterized by X-ray diffraction, secondary ion mass spectroscopy, and photoluminescence analysis which revealed increased dislocation density, high C impurity compensation of free carriers and yellow luminescence for low pressure samples. For GaN grown at 200 Torr pressure, the formation of highly resistive buffer with C concentration as high as 3.8 ×1017 cm-3 leads to reduced buffer leakage over one order of magnitude and an enhanced breakdown voltage of 425 V for a HEMT with gate–drain spacing of 4 µm. However, unlike atmospheric pressure grown samples, the presence of unintentional C in the semi-insulating GaN degraded the channel conduction and resulted in severe current collapse.