Spatial location of the Ec-0.6 eV electron trap in AlGaN/GaN heterojunctions

Abstract

Deep trap spectra in AlGaN/GaN high electron mobility transistor (HEMT) structures were studied by capacitance deep level transient spectroscopy. A major trap with an ionization level near Ec-0.6 eV was detected and attributed to states in the GaN buffer close to the AlGaN interface. These states have a signature very similar to the previously reported traps in AlGaN/GaN HEMTs responsible for the device degradation under electric stress.

Deep traps in GaN-based structures as affecting the performance of GaN devices

“…The 0.6 eV trap was similar to the trap pinning the Fermi level in the GaN:Fe buffer and could be associated with the main center in the buffer. However, the high sheet density of these traps on the order of 10 12 cm À2 suggests that we rather observed the accumulation of such traps near the AlGaN/GaN interface [187]. This accumulation was more prominent after oxygen annealing at 750-800 8C [186] (see Fig.…”

“…In MOCVD grown GaN:Fe buffers of the AlGaN/GaN HEMT structures, the two different states of that kind, one with the level near E c À0.59 eV and electron capture cross section of 3.3 Â 10 À13 cm 2 , the other at E c À0.6 eV and the electron capture cross section 6.8 Â 10 À15 cm 2 , could be clearly seen [186,187]. The latter trap pinned the Fermi level in the semi-insulating buffer as determined by PICTS that also showed the presence of a deeper center near E c À0.8 eV or E v +0.8 eV (PICTS cannot easily discriminate between the traps in the upper and lower half of the bandgap [186]).…”

“…The ET9 centers with levels near E c À0.52-0.55 eV are encountered in MOCVD and MBE-grown undoped n-GaN films, often together with the deeper ET10 traps at E c À0.6 eV [186,187]. Not much is known about the nature of these traps.…”

“…ODLTS measurements performed on oxygen-annealed AlGaN/ GaN(Fe) structures in Ref. [187] (Fig. 48) revealed the presence of several hole traps H1 (1.1 eV, s p = 4.2 Â 10 À12 cm 2 ), H2 (0.41 eV, 2.3 Â 10 À15 cm 2 ), H3 (0.28 eV, 2.3 Â 10 À16 cm 2 ) not present in the semi-insulating GaN(Fe) buffer probed by photoinduced current transient spectroscopy (PICTS) spectra measurements (s p here is the hole capture cross section).…”

Identifying the spatial position and properties of traps in GaN HEMTs using current transient spectroscopy

“…In this device, both Tp1 and Tp2 have been found to be thermally activated with E a = 0.65eVand0.37eV, respectively. Traps with the similar levels have been reported and identified in the GaN buffer close to the interface (~0.6 eV) [29], in heterostructure's interface (0.642 eV) [30], in the GaN film (0.59-0.63 eV) attributed to the edge dislocations by DLTS [31], in AlGaN barrier layer (0.3 eV-0.54e V) detected from transconductance dispersion and admittance curves [26], and in the AlGaN layer (0.37 eV) based on dynamic on-resistance (NDR) [32], respectively. It was suggested that Tp1 in the GaN layer are close to the AlGaN/GaN interface [29][30][31].…”