Study of the Effects of GaN Buffer Layer Quality on the dc Characteristics of AlGaN/GaN High Electron Mobility Transistors

The influence of different buffer layer quality on AlGaN/GaN high electron mobility transistors (HEMTs) dc characteristics was investigated. Dc measurement by parameter analyzer and gate pulse measurement were performed to compare two different buffer layer quality samples. The same Al concentrations of AlGaN with 2µm and 5µm GaN buffer layers on sapphire substrates from two different vendors were used. The defect densities of 2 µm and 5 μm GaN buffer layer's HEMTs structures measured by transmission electron microscopy (TEM) were 7 × 109 cm-2 and 5 × 108 cm-2, respectively. There was small difference in drain saturation current and transfer characteristics in HMETs for these two types of buffer. Non-passivated HEMT with 5 µm GaN buffer layer showed no dispersion in gate-lag pulsed measurement at 100 kHz but HEMT with 2 µm GaN buffer layer showed 71% drain current reduction at 100 kHz gate-lag pulsed measurement.