Deep level optical and thermal spectroscopy of traps in n-GaN grown by ammonia molecular beam epitaxy

Abstract

Deep level transient spectroscopy in plasma-assisted molecular beam epitaxy grown Al 0.2 Ga 0.8 N / GaN interface and the rapid thermal annealing effectThe incorporation of deep level defects in n-type GaN grown by ammonia-based molecular beam epitaxy ͑MBE͒ is studied via systematic adjustment of the NH 3 / Ga flux ratio. Deep level optical and transient spectroscopies, which together enable deep level detection throughout the GaN bandgap, reveal defect states whose individual concentrations vary with the NH 3 / Ga flux ratio. A general trend of lower concentration for deep levels at E C − 3.28, E C − 1.28, E C − 0.62, and E C − 0.25 eV with higher NH 3 / Ga flux ratio was observed, with the strongest reduction at the E C − 0.25 eV level, consistent with expectations for a V N -related defect. The known C N impurity state at E C − 3.28 eV and suspected C I -related state at E C − 1.28 eV also showed a moderate decrease in concentration at the higher NH 3 / Ga flux ratio. In contrast, the V Ga -related defect at E C − 2.62 eV was insensitive to the NH 3 / Ga flux ratio over the range studied here. Taken together, ammonia-MBE GaN has deep level defects with different sensitivities in flux ratios suggestive of independent physical sources. However, the total trap concentrations were significantly reduced for higher NH 3 / Ga flux ratios in n-type GaN grown by ammonia-MBE under the range of growth conditions used in this study, suggesting that higher NH 3 / Ga flux ratios will generate higher electronic quality GaN material when using ammonia-based MBE for device applications.

Deep level defects in Ge-doped (010) β-Ga2O3 layers grown by plasma-assisted molecular beam epitaxy

“…Concentrations of each state are found from the magnitude of the SSPC step until the onset of the next deepest energy level shown in Fig. 7(b) according to 26,32 …”

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

“…Hall, AS, DLTS [193,194] ET2 0.12-0.14 2 Â 10 À16 DLTS [197][198][199] [138,206,207,222] correlation of the ET2 traps density with the X-ray rocking curve half-width has been reported [200] suggesting that the traps could be related to dislocations. The logarithmic dependence of the DLTS peak height on the length of the injection pulse supports the assignment of the ET2, ET3 traps with localized centers on dislocations [197][198][199] (this is based on the well known work of Wosinsky in GaAs [11] that explains such logarithmic dependence by the correlated capture by the centers located on the dislocation line).…”

“…ET7 centers with levels near E c À0.4 eV are oftentimes detected in undoped n-GaN layers grown by MBE, particularly, under N-rich conditions [206,207]. These traps were also observed in some nonpolar multi-quantum-well (MQW) GaN/InGaN samples where they were adjacent to the GaN/InGaN MQW region [211].…”

“…DLTS spectra measurements on n-GaN grown by MBE whilst varying the N to Ga flux strongly suggest that the ET5 defects formation is favored by the N-rich growth conditions [206]. The logarithmic dependence of the DLTS peak on the injection pulse length provides serious grounds for assigning the ET5 centers to nitrogen vacancies (or their complexes) decorating dislocations [206,207].…”

Point Defects in GaN

“…It would be logical to assign the E c À2.6 eV signal to a C-related defect. However, Armstrong et al (2004), Arehart et al (2008), andZhang et al (2012) assigned the E c À2.6 eV signal to the V Ga defect.…”