Evolution of deep centers in GaN grown by hydride vapor phase epitaxy

Abstract

Deep centers and dislocation densities in undoped n GaN, grown by hydride vapor phase epitaxy (HVPE), were characterized as a function of the layer thickness by deep level transient spectroscopy and transmission electron microscopy, respectively. As the layer thickness decreases, the variety and concentration of deep centers increase, in conjunction with the increase of dislocation density. Based on comparison with electron-irradiation induced centers, some dominant centers in HVPE GaN are identified as possible point defects.

Traps in AlGaN∕GaN∕SiC heterostructures studied by deep level transient spectroscopy

“…Actually, trap A 1 has been repeatedly observed in thin GaN layers grown by various techniques and is often associated with line defects, i.e., dislocations. [7][8][9][10] This trap was also reported in AlGaN/ GaN HEMTs by measuring drain leakage current at different temperatures 2 and current DLTS. 4 On the other hand, trap A 2 can be induced by electron irradiation, simultaneously with another well-known trap, E ͑0.16 eV͒.…”

Plasma-etching-enhanced deep centers in n-GaN grown by metalorganic chemical-vapor deposition

“…According to a detailed study by Wosinski 7 of a dislocation-related electron trap ͑a line-defect͒ in plastically deformed n-type GaAs crystals, an increase in the slope of the n T versus ln(W f ) lines means an increase in the density of strain-related dislocations. Therefore, in our case, we believe that the plasma treatments do not cause any meaningful increase in dislocation density, even under an etching biasvoltage of Ϫ150 V. Trap D, with E T ϭ0.23-0.27 eV and n ϭ(1 -2)ϫ10 Ϫ15 cm 2 , has been observed in thin GaN layers by many groups, using various techniques, including hydride vapor phase epitaxy ͑HPVE͒, [8][9][10] MOCVD, [11][12][13] and MBE. 14,15 Three of these studies are consistent with the proposition that trap D is at least sometimes related to threading dislocations.…”

“…Trap D, owing to its association with high dislocation density, could be a complex of V N -V Ga , as discussed in Ref. 10. Furthermore, trap C has been associated with RIE-induced surface damage in free-standing GaN.…”

“…For example, the concentration of trap D in HVPE GaN increases with increasing dislocation density, corresponding to decreasing epilayer thickness. 9,10 Furthermore, the concentration of trap E 1 ͑similar to trap D͒ in MOCVD GaN increases with increasing concentration of edge dislocations, as measured by the broadening of the ͑102͒ Bragg peak as the buffer-layer growth rate is reduced. 13 We can summarize our major results as follows: ͑i͒ trap D and the other traps are bulk-like in the unetched sample; ͑ii͒ trap D is greatly enhanced by plasma-etching at high bias-voltages, but the additional trap-D concentration is closer to the surface; ͑iii͒ traps A 1 , C, and E 1 are also enhanced in the surface region; and ͑iv͒ all of these traps behave as dislocation-related line defects.…”

Optical investigation of shallow acceptor states in GaN grown by hydride vapor-phase epitaxy

“…Indeed, recent TEM studies have shown a decrease of dislocation and defect densities with the thickness of HVPE films. 13,14 This conclusion is further confirmed by comparing the low temperature PL features of the 3.5-m-HVPE layer with those of a 2-m-homoepitaxial GaN layer grown by MOCVD ͑see Fig. 3͒, where the latter was shifted by 4.9 meV to higher energy side in order to align the free A-exciton peaks.…”