New developments in theoretical studies of defects and impurities in III-Nitrides as pertinent to compensation and recombination in these materials are discussed. New results on experimental studies on defect states of Si, O, Mg, C, Fe in GaN, InGaN, and AlGaN are surveyed. Deep electron and hole traps data reported for GaN and AlGaN are critically assessed. The role of deep defects in trapping in AlGaN/GaN, InAlN/GaN structures and transistors and in degradation of transistor parameters during electrical stress tests and after irradiation is discussed. The recent data on deep traps influence on luminescent efficiency and degradation of characteristics of III-Nitride light emitting devices and laser diodes are reviewed.

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

In high-purity GaN grown by hydride vapor phase epitaxy, the commonly observed yellow luminescence (YL) band gives way to a green luminescence (GL) band at high excitation intensity. We propose that the GL band with a maximum at 2.4 eV is caused by transitions of electrons from the conduction band to the 0/+ level of the isolated ${\mathrm{C}}_{\mathrm{N}}$ defect. The YL band, related to transitions via the \ensuremath{-}/0 level of the same defect, has a maximum at 2.1 eV and can be observed only for some high-purity samples. However, in less pure GaN samples, where no GL band is observed, another YL band with a maximum at 2.2 eV dominates the photoluminescence spectrum. The latter is attributed to the ${\mathrm{C}}_{\mathrm{N}}{\mathrm{O}}_{\mathrm{N}}$ complex.

/pdf/carbon-defects-as-sources-of-the-green-and-yellow-2vq3am07g5.pdf

Carbon defects as sources of the green and yellow luminescence bands in undoped GaN

http://absimage.aps.org/image/MAR15/MWS_MAR15-2014-001413.pdf

Acceptor defects and impurities play a critical role in the performance of GaN-based devices. Mg is the only acceptor impurity that gives rise to p-type conductivity, while other acceptors (such as CN impurities and VGa defects) act as sources of compensation and trapping. From the point of view of theory, understanding the physics of acceptor species in GaN has long been a challenge. In the past, limitations of computational techniques made it difficult to quantitatively predict crucial quantities such as thermodynamic and optical transition levels. However, advances in first-principles calculations, including the use of hybrid functionals in density functional theory, have led to a resurgence in efforts to understand properties of acceptors in nitrides. After briefly discussing advances in theoretical techniques, we review recent computational work on acceptor impurities in GaN and compare theoretical results with the available experimental data. We also present new hybrid density functional calculations on the transition levels of VGa and its complexes with O and H impurities. The results indicate that donor impurities significantly lower VGa transition levels, and that VGa3H and VGaON2H complexes give rise to yellow luminescence. We also discuss the properties of acceptor impurities in AlN and InN.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/pssb.201552062

First‐principles theory of acceptors in nitride semiconductors

Quantum technology has grown out of quantum information theory and now provides a valuable tool that researchers from numerous fields can add to their toolbox of research methods. To date, various systems have been exploited to promote the application of quantum information processing. The systems that can be used for quantum technology include superconducting circuits, ultracold atoms, trapped ions, semiconductor quantum dots, and solid-state spins and emitters. In this review, we will discuss the state-of-the-art of material platforms for spin-based quantum technology, with a focus on the progress in solid-state spins and emitters in several leading host materials, including diamond, silicon carbide, boron nitride, silicon, two-dimensional semiconductors, and other materials. We will highlight how first-principles calculations can serve as an exceptionally robust tool for finding novel defect qubits and single-photon emitters in solids, through detailed predictions of electronic, magnetic, and optical properties.

Material platforms for defect qubits and single-photon emitters

We demonstrate that yellow luminescence often observed in both carbon-doped and pristine GaN is the result of electronic transitions via the C(N)-O(N) complex. In contrast to common isolated defects, the C(N)-O(N) complex is energetically favorable, and its calculated optical properties, such as absorption and emission energies, a zero phonon line, and the thermodynamic transition level, all show excellent agreement with measured luminescence data. Thus, by combining hybrid density functional theory and experimental measurements, we propose a solution to a long-standing problem of the GaN yellow luminescence.

Yellow luminescence of gallium nitride generated by carbon defect complexes.

The blue luminescence band with a maximum at 3.0 eV and the zero-phonon line at 3.33 eV (labeled BL2) is observed in high-resistivity GaN. Under prolonged ultraviolet (UV) light exposure, the BL2 band transforms into the yellow luminescence (YL) band with a maximum at 2.2 eV. Our hybrid functional calculations suggest that the BL2 band is related to a hydrogen-carbon defect complex, either CNON-Hi or CN-Hi. The complex creates defect transition level close to the valence band, which is responsible for the BL2 band. Under UV illumination, the complex dissociates, leaving as byproduct the source of the YL band (CNON or CN) and interstitial hydrogen.

Hydrogen-carbon complexes and the blue luminescence band in GaN

Gallium nitride is an attractive, important system for high-power electronics, but device performance is limited by the presence of intrinsic point defects, which are present even in material of the highest purity. Over the past 20 years, many contradictory results about these defects have emerged from both experiment and theory. The authors use a state-of-the-art approach to calculate electronic and optical properties of all common, native defects in GaN, and compare the results to experiment. They also show the likelihood of native defects to be radiative or nonradiative, which is important for improving device fabrication.

/pdf/native-point-defects-in-gan-a-hybrid-functional-study-2je75w76c3.pdf

Native Point Defects in GaN: A Hybrid-Functional Study

http://absimage.aps.org/image/MAR16/MWS_MAR16-2015-002052.pdf

Hydrogen-carbon complexes and the blue luminescence band in GaN.

The problem of magnesium acceptor in gallium nitride is that experimental photoluminescence measurements clearly reveal a shallow defect state, while most theoretical predictions favor a localized polaronic defect state. To resolve this contradiction, we calculate properties of magnesium acceptor using the Heyd-Scuseria-Ernzerhof (HSE) hybrid functional, tuned to fulfill the generalized Koopmans condition. We test Koopmans tuning of HSE for defect calculations in GaN using two contrasting test cases: a deep state of gallium vacancy and a shallow state of magnesium acceptor. The obtained parametrization of HSE allows calculations of optical properties of acceptors using neutral defect-state eigenvalues, without relying on corrections due to charged defects in periodic supercells. Optical transitions and vibrational properties of $\mathrm{M}{\mathrm{g}}_{\mathrm{Ga}}$ defect are analyzed to bring the dual (shallow and deep) nature of this defect into accord with experimental photoluminescence measurements of the ultraviolet band in Mg-doped GaN samples.

https://link.aps.org/accepted/10.1103/PhysRevB.97.205205

Magnesium acceptor in gallium nitride. II. Koopmans-tuned Heyd-Scuseria-Ernzerhof hybrid functional calculations of its dual nature and optical properties

I. C. Diallo

Papers

Yellow luminescence of gallium nitride generated by carbon defect complexes.

Hydrogen-carbon complexes and the blue luminescence band in GaN

Native Point Defects in GaN: A Hybrid-Functional Study

Hydrogen-carbon complexes and the blue luminescence band in GaN.

Magnesium acceptor in gallium nitride. II. Koopmans-tuned Heyd-Scuseria-Ernzerhof hybrid functional calculations of its dual nature and optical properties