Deep-level defects and n-type-carrier concentration in nitrogen implanted GaN

Abstract

We analyzed the intrinsic defects and the n-type-carrier concentration generated by nitrogen ion implantation in n-type GaN by deep-level-transient spectroscopy and by capacitance–voltage measurements, respectively. The samples were grown on sapphire by metalorganic vapor-phase epitaxy. Nitrogen implantation with different ion doses and postimplantation rapid-thermal annealing (RTA) were investigated. We observed a growing n-type-carrier concentration and increasing defect concentration with increasing nitrogen ion implantation doses. After RTA the concentration of free carriers and deep levels as found in the as-grown state are restored. We also address contrarily seeming results from measurements of sheet resistance after N implantation published recently.

Deep centers in n-GaN grown by reactive molecular beam epitaxy

“…3, is close to E 3 ͑0.665 eV͒ 3 and D3 ͑0.67 eV͒. 4 Trap B, peaked at ϳ335 K with E T ϭ0.62 eV and T ϭ7.4 ϫ10 Ϫ15 cm 2 , which is close to E 2 ͑0.58 eV͒, D2 ͑0.60 eV͒, and DLN 3 ͑0.59 eV͒ reported by Hacke et al, 3 Haase et al, 4 and Götz et al, 5 respectively, was also found 7 to be a dominant trap in both MOCVD and HVPE GaN layers, with trap densities from 1 to 2ϫ10 14 cm Ϫ3 . Trap D, peaked at ϳ160 K with E T ϭ0.24 eV and T ϭ2.0ϫ10 Ϫ15 cm 2 , which is close to E 1 ͑0.264 eV͒ 3 and DLN 1 ͑0.25 eV͒, 5 was also found 7 in both MOCVD and HVPE GaN, but with trap densities in the low-10 14 cm Ϫ3 .…”

“…Based on the effects of 270-keV N 2ϩ implantation and annealing, Haase et al have suggested that two centers, D2 and D3, with activation energies of 0.60 and 0.67 eV, are the N antisite and N interstitial, respectively. 4 Recently, some of the present authors have reported an electron-irradiation-induced trap, located at E C -0.18 eV, in both MOCVD and HVPE GaN. This trap is most likely associated with the N vacancy.…”

“…8, the crystal stoichiometry or the N richness of RMBE GaN films seems to be determined mainly by the growth temperature, rather than the ammonia flow rate. ͑Note that the ammonia cracking rate is strongly temperature dependent.͒ On the other hand, the dominance of trap B, which is close to trap D2, 4 in both MOCVD and HVPE GaN materials, implies that these materials are more N rich, since the center D2 has been tentatively identified to be related to the N-antisite defect, based on a study of N 2ϩ implantation and annealing, 4 as mentioned above.…”

“…A number of deep centers in n-GaN, measured by deep-level transient spectroscopy ͑DLTS͒, with activation energies in the range of 0.15-0.8 eV and trap densities in the range of 10 13 -10 15 cm Ϫ3 , have been reported by several groups. [3][4][5] Most of the studies have so far dealt with n-GaN materials grown by either metalorganic chemical-vapor deposition ͑MOCVD͒ or hydride vapor-phase epitaxy ͑HVPE͒. The origin of the observed deep centers remains an open question.…”

Radiation-induced defects in GaN bulk grown by halide vapor phase epitaxy

“…In a later study, Fang et al suggested the peak to be related to the divacancy V N -V Ga . 18 The trap D3 at $Ec-0.60 eV has been previously reported 10,11,16,19,20 and one of the suggested defect models is the N antisite (N Ga ). 19 However, later studies of electronirradiated HVPE-grown GaN 21 ruled out the model of a simple intrinsic defect since no change of the concentration was observed after irradiation.…”