The stability, electronic and optical properties of nonmetal doped g-GaN: A first-principles calculation

First-principles theoretical results are presented for substitutional and interstitial carbon in wurtzite GaN. Carbon is found to be a shallow acceptor when substituted for nitrogen (CN) and a shallow donor when substituted for gallium (CGa). Interstitial carbon (CI) is found to assume different configurations depending on the Fermi level: A site at the center of the c-axis channel is favored when the Fermi level is below 0.9 eV (relative to the valence band maximum) and a split-interstitial configuration is favored otherwise. Both configurations produce partly filled energy levels near the middle of the gap, and CI should therefore exhibit deep donor behavior in p-type GaN and deep acceptor behavior in n-type GaN. Formation energies for CN, CGa, and CI are similar, making it likely that CN acceptors will be compensated by other carbon species. CGa is predicted to be the primary compensating species when growth occurs under N-rich conditions while channel CI is predicted to be the primary compensating species under Ga-rich growth conditions. Self-compensation is predicted to be more significant under Ga-rich growth conditions than under N-rich conditions. Experimental evidence for self-compensation is discussed. Four carbon complexes are discussed. CN–VGa is found to be unstable when the Fermi level is above the middle of the gap due to the high stability of gallium vacancies (VGa). The CN–VGa complex was previously suggested as a source of the broad 2.2 eV luminescence peak often observed in n-type GaN. The present results indicate that this is unlikely. The CI–CN complex is capable of forming in carbon doped GaN grown under Ga-rich conditions if the mobility of the constituents is high enough. Experimental evidence for its existence is discussed.

This brief report examines the influence of Ga/N flux conditions on Mn incorporation in GaN. Mn-doped GaN layers were grown at 680 °C by molecular beam epitaxy on a Ga-polar GaN(0001) template substrate under Ga-rich, N-rich, and no-flux conditions (i.e., Mn δ doping). Mn incorporation was the highest under an N-rich condition, lowest under a Ga-rich condition, and intermediate in the absence of Ga and N fluxes. For the growth conditions examined in this study, the corresponding Mn sticking coefficients, relative to that of the N-rich condition, were determined to be 0.31 for no-flux growth and 0.01 for the Ga-rich growth.

Growth of high-quality cubic GaN on Si (0 0 1) coated with ultra-thin flat SiC by plasma-assisted molecular-beam epitaxy

Ab initio study for adsorption and desorption behavior at step edges of GaN(0001) surface

Self-assembled GaN nano-rods grown directly on (1 1 1) Si substrates: Dependence on growth conditions

Stress dependence on N/Ga ratio in GaN epitaxial films grown on ZnO substrates

First-principles study of the effects of interstitial H and point vacancies on the photocatalytic performance of Be/Mg/Ca-doped GaN

The effects of nonmetal dopants on the electronic, optical and chemical performances of monolayer g–C3N4 by first-principles study

We have evaluated the long-term electrical reliability of GaN/AlGaN high-electron-mobility transistors grown under Ga-rich, N-rich, and NH3-rich conditions. Vpinch-off shifts positively after stress for devices grown under Ga-rich and N-rich conditions, while it shifts negatively for NH3-rich devices. Density functional theory calculations suggest that the hot-electron-induced release of hydrogen from hydrogenated Ga-vacancies is primarily responsible for the degradation of devices grown in Ga-rich and N-rich conditions, while hydrogenated N-antisites are the dominant defects causing degradation in devices grown under NH3-rich conditions.

GaMnN layers have been grown on GaAs(0 0 1) substrates by plasma-assisted molecular beam epitaxy (PAMBE), under both N-rich and Ga-rich conditions, at temperatures from 680 °C down to 186 °C. Under N-rich conditions, a reduction in the growth temperature results in a transition from faulted single-crystalline zinc-blende layer growth to mixed-phase zinc-blende and wurtzite polycrystalline layer growth, whilst being also associated with increasing levels of Mn incorporation. Improved layer crystallinities were associated with PAMBE growth under Ga-rich conditions. In particular, a tilted, mixed-phase growth mode allowing for the deposition of comparably uniform GaMnN alloys, at a level of ∼3.5 at% Mn, was identified for slightly Ga-rich conditions at a reduced temperature of ∼265 °C. No correlation could be established between the GaMnN/GaAs (0 0 1) fine-scale defect structures and the layer functional properties, with all the free-standing layers showing p-type conductivities and comparable mobilities.

Highly efficient and reproducible p-type doping of GaN under nitrogen-rich and low-growth-temperature conditions was demonstrated with the plasma-assisted molecular beam epitaxy technique. The low-temperature range is approximately below 650 °C and refers to growth temperatures at which the thermal desorption of any excess Ga is negligibly slow. The Mg and hole concentrations obtained with the N-rich condition were more than one order of magnitude higher than those obtained with the Ga-rich condition while keeping all other conditions identical. The Mg doping under such N-rich conditions was also found to show Mg-mediated suppression of background impurities, good epitaxy quality on GaN templates, and relatively low surface roughness. Over the investigated growth temperature range from 580 °C to 650 °C, the Mg incorporation efficiency under the N-rich condition was found to be close to unity (70%-80%) and independent of the growth temperature. High hole concentrations of up to 2×1019 cm-3 and activation efficiencies of up to 16.6% were obtained. The result rules out the Mg surface sticking probability as the limiting mechanism for Mg incorporation in this temperature range, as it would be temperature dependent. Instead, the Mg incorporation rate was more likely governed by the availability of substitutional sites for Mg on the surface, which should be abundant under the N-rich growth conditions. Excellent diode characteristics and electroluminescence results were observed when this p-type doping method was employed in the growth of full device structures.

Al x Ga 1−x N films were grown by plasma-assisted molecular-beam epitaxy on (0001) sapphire substrates under Ga-rich conditions. To control the AlxGa1−xN composition over the entire range, the Al and Ga arrival rates were fixed while the nitrogen arrival rate was varied. We have found that the Al fraction increased with decreasing N flow due to preferentially favorable bonding of Al and N over Ga and N. Consequently, the growth rate decreased as the Al mole fraction increased. A photoluminescence quantum efficiency at 15 K was markedly higher for the AlxGa1−xN layers grown under Ga-rich conditions (3%–48%) compared to the layers grown under N-rich conditions (1%–10%), indicating much reduced nonradiative recombination in samples grown under Ga-rich conditions.

Hexagonal GaN films were grown on Si(111) covered with a thin flat SiC buffer layer under both N- and Ga-rich growth conditions. A flat 2.5-nm-thick SiC layer was an effective buffer layer for GaN growth. The growth mode and microstructure of GaN depended strongly on the Ga/N flux ratios. Under N-rich growth conditions, the growth mode was three dimensional; GaN showed statistical roughening of the surface and a characteristic columnar structure. Under Ga-rich conditions, the GaN growth mode was two dimensional; GaN films with a flat surface and an almost stacking-fault-free microstructure were obtained. The two-dimensional growth mode was facilitated by strong wetting between Ga and SiC(111) at the first Ga-layer deposition on SiC.

We present a detailed study of Mg acceptor, p-type doping of GaN grown by plasma-assisted molecular beam epitaxy in both Ga-rich and N-rich conditions at low (∼580 °C) to high growth temperatures (∼740 °C). A growth map is constructed using results from a broad range of growth conditions, which shows the dependence of Mg incorporation and surface roughness on the III/V ratio and growth temperatures. Detailed secondary ion mass spectroscopy and atomic force microscopy studies confirmed that N-rich conditions are favorable for significantly higher Mg-incorporation efficiency (∼80%), whereas the Ga-rich growth condition is preferable for achieving a smooth surface morphology (root mean square roughness: ∼1–2 nm) with poor Mg incorporation. The room temperature Hall measurement confirms that the hole concentration in the range of ∼7 × 1017 to 2 × 1019 cm−3 can be achieved in Ga-rich and N-rich conditions, respectively, at a fixed Mg flux depending on the growth conditions. Our detailed study provides a proper guideline for realizing an efficient Mg-doped GaN layer and is applicable, in principle, to different nitride-based electronic and photonic devices.

In order to construct efficient solar-driven devices, many potential materials have been explored in search of desirable photocatalyts for water splitting. Layered structure nitride halides have received significant attention from different fields because of their unusual electronic properties. In this work, we have systematically studied the electronic structures and potential photocatalytic properties of single-layer Group-IVB nitride halides (MNX, M = Ti, Zr, Hf; X = Cl, Br, I) in different forms using first-principles calculations. The results show that the single-layer nitride halides have very low formation energies, which indicates that the isolation of these single-layer MNX materials should not be difficult. The calculated band structures reveal that all of the single-layer MNX are semiconductors, while each of them shows a distinct type of electronic properties. Among these semiconducting nitride halides, ten members of the single-layer MNX family are feasible photocatalysts for splitting water. Interestingly, single-layer α-ZrNX (X = Cl, Br, I) and α-HfNI are direct band gap semiconductors with desirable band gaps (2.23–2.83 eV), and the calculated optical adsorption spectra further confirm their excellent light absorption in visible light region. Finally, the electronic properties and optical absorption in visible light region of single-layer MNX can be easily tuned through hybridisation or doping between them because of the similarity of the MNXs. Their high stability, versatile electronic properties, and high optical absorption make single-layer Group-IVB nitride halides promising candidates for application in photocatalytic water splitting.