A first-principles study of carbon-related energy levels in GaN. I. Complexes formed by substitutional/interstitial carbons and gallium/nitrogen vacancies

Abstract

Various forms of carbon based complexes in GaN are studied with first-principles calculations employing Heyd-Scuseria-Ernzerhof hybrid functional within the framework of density functional theory. We consider carbon complexes made of the combinations of single impurities, i.e. CN − CGa, CI − CN and CI − CGa, where CN, CGa and CI denote C substituting nitrogen, C substituting gallium and interstitial C, respectively, and of neighboring gallium/nitrogen vacancies (VGa/VN), i.e. CN − VGa and CGa − VN. Formation energies are computed for all these configurations with different charge states after full geometry optimizations. From our calculated formation energies, thermodynamic transition levels are evaluated, which are related to the thermal activation energies observed in experimental techniques such as deep level transient spectroscopy. Furthermore, the lattice relaxation energies (Franck-Condon shift) are computed to obtain optical activation energies, which are observed in experimental techniques such as deep level optical spectroscopy. We compare our calculated values of activation energies with the energies of experimentally observed C-related trap levels and identify the physical origins of these traps, which were unknown before.

A first-principles study of carbon-related energy levels in GaN. II. Complexes formed by carbon and hydrogen, silicon or oxygen

“…The former is obtained by thermal techniques such as DLTS, whereas the latter is obtained by optical techniques such as DLOS. In our previous paper 5 , we assigned the origins of these experimentally observed trap levels to the calculated results obtained by our HSE calculations for carbon-carbon/carbon-vacancy complexes. These assignments are also presented in the right column of Table I.…”

“…In case of the 3+ charge state, the C atom forms a type 3 split interstitial sharing the site with an N atom making a dimer, which is defined in Ref. 5. This configuration is shown in Fig.…”

“…This manuscripts is organized as follows: in Section II, the computational methods are briefly outlined as the detail are similar to the ones presented in our companion work 5 . In Section III, we will present our calculated results for H, Si and O impurities and complexes with C. Our theoretical trap levels are assigned to experimentally observed ones and concentration analysis is performed in Section IV.…”

Electrically active point defects in Mg implanted n-type GaN grown by metal-organic chemical vapor deposition

“…Carbon, which is also present in high concentrations in our samples, can also form complexes with either V Ga or V N , but such complexes possess very high formation energies. 20 A more plausible hypothesis would be the formation of Si-related complexes. As a matter of fact, it was shown that a V Ga -complex, formed with Si, gives rise to an acceptor in FIG.…”

“…19 For these reasons, the hypothesis of an impurity (C or H)-related complex might be favored. As a matter of fact, a DFT study performed by Matsubara and Bellotti 20 reported a level at E C -0.22 eV for the C Ga V N complex.…”