Increased p-type conductivity in GaNxSb1−x, experimental and theoretical aspects

Abstract

The large increase in the p-type conductivity observed when nitrogen is added to GaSb has been studied using positron annihilation spectroscopy and ab initio calculations. Doppler broadening measurements have been conducted on samples of GaN x Sb 1Àx layers grown by molecular beam epitaxy, and the results have been compared with calculated first-principle results corresponding to different defect structures. From the calculated data, binding energies for nitrogen-related defects have also been estimated. Based on the results, the increase in residual hole concentration is explained by an increase in the fraction of negative acceptor-type defects in the material. As the band gap decreases with increasing N concentration, the ionization levels of the defects move closer to the valence band. Ga vacancy-type defects are found to act as positron trapping defects in the material, and the ratio of Ga vacancy-type defects to Ga antisites is found to be higher than that of the p-type bulk GaSb substrate. Beside Ga vacancies, the calculated results imply that complexes of a Ga vacancy and nitrogen could be present in the material. V C 2015 AIP Publishing LLC.

Intrinsic point defects and the n - and p -type dopability of the narrow gap semiconductors GaSb and InSb

“…As Sb Ga are positively charged and Ga Sb and V Ga negatively charged for E F within the band gap, these defects self compensate and one would expect E F to remain trapped roughly midgap, resulting in an intrinsically insulating material (we note that the formation energy of Ga i is also low in this range of E F and we expect that this defect will play a minor rôle in the self-compensation mechanism). These formation energies suggest significant concentrations of V Ga will be present, in agreement with PAS studies, [53][54][55]109 but the insulating nature contradicts the p-type activity of GaSb observed in many differently produced samples. It may be the case that, in non-equilibrium growth techniques, formation of the compensating Sb Ga may be suppressed, which would result in a p-type material where the hole concentration arises from the ionisation of V Ga and Ga Sb .…”

“…As-grown GaSb has been shown to be p-type regardless of growth conditions, 12,16,[47][48][49][50] although the acceptor concentrations can be decreased slightly by varying the V/III flux when growing with molecular beam epitaxy (MBE). 51,52 Gallium vacancies (V Ga ) have been shown to occur in GaSb using positron annihilation spectroscopy (PAS), 53 but have been ruled out as the dominant acceptor; instead, it has been inferred in further PAS studies that the gallium antisite (Ga Sb ) is responsible for the observed p-type activity, 54,55 based on earlier density functional theory (DFT) calculations using the local density approximation (LDA). 56 While the LDA was also used to investigate the rôle of H in GaSb, 57 this approach suffers from the well-known band gap underestimation error, which is particulary problematic in narrow gap semiconductors such as GaSb and InSb.…”

Reactively Sputtered Sb-GaN Films and its Hetero-Junction Diode: The Exploration of the n-to-p Transition

“…The n-to-p conversion by incorporating Sb is special. Limited data were reported for the group V anion instead of cation doping on GaN [18][19][20][21][22]. Our work can have its contribution on the HMA field for further development.…”

Instability of the Sb vacancy in GaSb

“…In both irradiated samples, τ ave is higher after annealing than it is in as-grown GaSb indicating a permanent increase in the vacancy defect concentrations as a result of the irradiation. In previous studies, the positron lifetime at different vacancy-type defects in GaSb has been estimated both experimentally [22] and computationally [23]. An experimental positron lifetime of τ V Ga = 285 ps was estimated for the V Ga , an increase of 40 ps compared to the estimated bulk lifetime of τ B = 245 ps.…”

“…Most recent experimental and theoretical work show that V Ga and Ga Sb are the dominant acceptor-type native defects in GaSb [17,[21][22][23], but their relative importance depends on the crystallization conditions [21][22][23]. For Czochralski-grown bulk GaSb crystals the concentration of Ga antisites is an order of magnitude higher than that of the Ga vacancies, making the antisite the * natalie.segercrantz@aalto.fi main cause for p-type behavior.…”