Photoluminescence studies of impurity transitions in Mg-doped AlGaN alloys

Abstract

Deep ultraviolet photoluminescence spectroscopy was employed to study the impurity transitions in Mg-doped AlGaN alloys. A group of deep level impurity transitions was observed in Mg-doped AlxGa1−xN alloys, which was identified to have the same origin as the previously reported blue line at 2.8eV in Mg-doped GaN and was assigned to the recombination of electrons bound to the nitrogen vacancy with three positive charges (VN3+) and neutral Mg acceptors. Based on the measured activation energies of the Mg acceptors in AlGaN and the observed impurity emission peaks, the VN3+ energy levels in AlxGa1−xN have been deduced for the entire alloy range. It is demonstrated that the presence of high density of VN3+ deep donors translates to the reduced p-type conductivity in AlGaN alloys due to their ability for capturing free holes.

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

“…Fig. 19 reproduced from paper [126] shows that, in pAlGaN, a series of PL bands with energies ranging from 2.8 eV in GaN to 4.7 eV in AlN are systematically observed. These transitions were attributed to recombination involving Mg acceptors and triply charged nitrogen vacancies V N 3+ predicted by theory.…”

“…Straight Hall effect/conductivity measurements are relatively easy for Al mole fractions x < 0.2. For higher compositions p-type conductivity has only been reported for carefully optimized growth conditions minimizing the impact of compensating centers among which the prominent role of nitrogen vacancies has been noted (we'll return to this point later) [124][125][126][127][128].…”

“…Growing p-AlGaN with a higher V/III components ratio (and therefore, a reduced density of nitrogen vacancies) greatly suppressed the intensity of such PL lines in favor of more shortwavelength lines attributed to transitions from conduction band to Mg acceptors (respective PL bands at near 3.2 eV in GaN and at near 5.55 eV in AlN [126]). Fig.…”

“…[126] illustrates the proposed levels scheme in the studied p-AlGaN of various compositions. It is suggested that growth under conditions suppressing the formation of V N improves the p-type conductivity in p-AlGaN and AlN due to the lower compensation ratio of Mg [125,126]. Problem here is, of course, that, although theory does in fact predict the predominance of V N 3+ triply charged donors as the major compensating defects in p-GaN and p-AlN [28,43], it places respective levels in the lower half of the bandgap, near E v +0.4 eV in p-GaN and close to E v +1 eV in AlN (see recent calculations in Ref.…”

“…20 taken from Ref. [126] illustrates the proposed levels scheme in the studied p-AlGaN of various compositions. It is suggested that growth under conditions suppressing the formation of V N improves the p-type conductivity in p-AlGaN and AlN due to the lower compensation ratio of Mg [125,126].…”