Defect Characterization in High-Electron-Mobility Transistors with Regrown p-GaN Gate by Low-Frequency Noise and Deep-Level Transient Spectroscopy

To investigate the defects from the gate regrowth process, samples with and without regrowth p-GaN process are fabricated by metalorganic chemical vapor deposition (MOCVD). The DC characteristics indicate larger gate leakage (I-gs) between the GaN channel and the p-GaN gate in the regrowth sample than in the nonregrowth counterpart. In addition, significant Si/O impurities are introduced by the regrowth process at the interface between channel and regrown AlGaN barrier. The low-frequency noise (LFN) measurement and deep-level transient spectroscopy (DLTS) are further carried out to investigate the defectivity at the AlGaN barrier and channel interface, giving a 2-3 times higher border trap density in the AlGaN barrier (depth approximate to 5 nm from the channel interface) and a 10 times increase in interface trap density at the channel interface, corresponding with a band of shallow levels E3 = E-c-0.02-0.15 eV. Three additional bulk traps E2/E5 (E-c-0.8 eV, sigma n=5x10-15 cm2 / E-c-0.17 eV, sigma n=5x10-22 cm2) and E4 (E-c-0.23 eV, sigma n=5x10-19 cm2) are also found in the regrowth and nonregrowth samples, respectively. Their possible spatial locations and origins are discussed.