Journal
JOURNAL OF ELECTRONIC MATERIALS
Volume 32, Issue 5, Pages 388-394Publisher
SPRINGER
DOI: 10.1007/s11664-003-0163-6
Keywords
AlGaN/GaN HEMTs; defects; surface passivation; AFM; DLTS; capacitance-voltage measurements; gate-lag measurements; current-voltage measurements; large signal measurements
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Device performance and defects in AlGaN/GaN high-electron mobility transistors (HEMTs) have been correlated. Surface depressions and threading dislocations, revealed by optical-defect mapping and atomic force microscopy (AM, compromised the effectiveness of the SiNx surface-passivation effect as evidenced by the gate-lag measurements. The residual carriers in the GaN-buffer layer observed from the capacitance-voltage depth profile have been attributed to the point defects and threading dislocations either acting as donors or causing local charge accumulations. Deep-level transient-spectroscopy measurements showed the existence of several traps corresponding to surface states and bulk-dislocation defects. The formation of electron-accumulation regions on the surface or (and) in the GaN-buffer layer was confirmed by current-voltage measurements. This second, virtual gate formed by electron accumulations can deplete the channel and cause a large-signal gain collapse leading to degraded output power. A good correlation was established between the device performance and defects in AlGaN/GaN HEMT structure.
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