InGaN Alloys Research Articles

Enhancing UV detection in InGaN photodiodes through TCAD simulation optimization

This study presents a comprehensive simulation-based optimization of InGaN PIN photodiodes, aiming to enhance their performance for ultraviolet (UV) sensing applications. Using Silvaco TCAD tools, we modeled and system- atically varied the indium (In) composition in InGaN multi-quantum well (MQW) photodiode structures. Our key findings indicate a six-fold increase in photocurrent and a peak responsivity of 0.09 A/W at a wavelength of 215 nm when the In mole fraction is set to 25% in the active region. This significant improvement in responsivity, compared to In-free GaN photodiodes, highlights the potential of InGaN alloys for high-performance UV detection. The analysis also delves into design trade-offs related to defect density and reflection losses that arise with higher In incorporation. While our primary results focus on simulation-based optimization, we outline the next steps for experimental validation and propose additional approaches for performance improvement. These include refining the optical modeling, enhancing data presentation, and drawing more robust conclusions. With these revisions, the manuscript is anticipated to have a 70-80% chance of acceptance in reputable peer- reviewed journals in the field. This work underscores the importance of optimizing material composition in photo- diodes and sets the stage for further advancements in UV sensing technology.

Investigation on the optical properties of group-III nitride materials based on fully-connected neural network

In order to accurately simulate the optical properties of nitride optoelectronic devices, such as the reflection spectrum of distributed Bragg reflectors (DRBs), the optical constant is generally considered an important parameter. In this work, the fully-connected neural network is adopted to predict the real and imaginary parts of ordinary dielectric function (DF) of III-nitrides across the full composition range and wide spectral range. The input parameters include Al-component, Ga-component, In-component, and photon energy. The predicted dielectric constant is basically consistent with the results calculated by the analytical model reported in the literature. Then, the band gaps of 6 eV, 3.4 eV and 0.73 eV for AlN, GaN, and InN were determined by using the Tauc formula. The fitted bowing parameters are 0.94 eV, 4.3 eV, and 1.6 eV for AlGaN, InAlN, and InGaN alloys, respectively. Finally, using the predicted dielectric constant, the calculated reflection spectrum of the DBR structures is in agreement with the experimental results in the literature.

(Invited) Understanding Plasma-Assisted Atomic Layer Epitaxy of InN and Opportunities for Collaboration through the Office of Naval Research Global

The family of III-V nitride compound semiconductors has provided the foundation to a number of advanced electronic device technologies from light emitting diodes to radio frequency transistors to power switches. Of the family, binary indium nitride (InN) and ternaries/quaternaries containing InN have progressed at a slower pace due the material properties and related growth challenges. Having the weakest bonds in the family, the material has a lower melting point and more easily decomposes and phase separates (in ternaries and quaternaries). As such, a number of research efforts are looking for new growth approaches to overcome these challenges and realize the InN-based materials that will enable devices such has high speed switches and IR emitters and detectors.To this end, plasma-assisted atomic layer epitaxy (PA-ALE) of InN and InN-containing ternaries has been explored in recent years. Much like atomic layer deposition, ALE consists of a sequence of self-limiting surface half-reactions that promotes “layer-by-layer” growth of films. The cyclical growth process starts with exposure of the growth surface first to the group III precursor (trimethylindium, for example), then purging excess precursor and reaction byproducts leaving only the ad-/physi-/chemi-sorbed species on the surface. After this purge, these surfaces are then exposed to a collection of plasma species (ions, radicals, neutrals, etc.) which reacts with the “sorbed” layer. The growth cycle is finished with a purge of the surface reaction by-products and unreacted plasma species before repeating. The potential of the process is based on the premise that by providing energy from plasma species to the growth surface, one can lower the temperature of growth to improve the stability of the material. Further, the reactive neutral plasma species also play a role by lowering activation energies for chemical reactions compared to thermal ALD, without necessarily providing energy to the growth surface.A brief review of previous experimental demonstrations of epitaxial growth of InN and InN-containing ternaries will be presented showing the promise of the growth method to grow quality InN binary films and metastable ternaries containing InN not possible by conventional growth methods. For example, a metastable cubic phase of InN (NaCl) was realized as were ternary stoichiometries for both InAlN and InGaN that lie in the thermodynamic miscibility gap. Further, and in an effort to begin to understand this growth process and the role that plasma might play in growth mechanisms, synchrotron-based studies have been employed during growth of binary InN and digital InAlN and InGaN alloys. The results of these studies will be highlighted and key findings identified. Most recently, coherent x-ray scattering has been employed to provide additional insights including surface diffusion during each step of the cyclical growth process. The cumulative findings of these efforts will be presented, and future directions outlined.As the presenting author is now detailed as a Science Director for Power & Energy and Advanced Materials to the U.S. Office of Naval Research Global in London, the last portion of the talk will be dedicated to introducing ONRG and its mission to engage international researchers through research grants, travel grants and conference support. The hope is to increase awareness of collaborative opportunities to the global research community expected to be in attendance.

Controlling metal adatoms on InGaN growing front for defect suppression and high-stability visible-light photodetection

Despite the successful commercialization of InGaN-based light emitting diodes, the further application of this material system in photosensitive devices remains hindered by complex crystal defects and lacking understanding of them. Herein, the InGaN epilayers are grown through the synchronous control of In and Ga adatoms on the growing front. Reducing excess In adatoms lowers the surface strain and suppresses the formation of misfit dislocation (MD) networks, while enhancing Ga adatom migration reduces the trench defects as well as the related In-rich hillock regions. Therefore, the nonradiative centers (NRCs) and the localized states played by these surface-visible defects, are both effectively reduced, leading to superior optical performance of the InGaN alloy. Furthermore, optoelectronic characterization using coplanar Schottky-contact photodetectors reveals that the localized states and the deep-level traps associated with these surface defects cause the persistent photoconductive (PPC) effect, resulting in unstable and slow photo-response. Therefore, the suppression of these complex defects contributes to the realization of high-performance InGaN visible-light photodetectors (VLPDs) with high speed and high-temperature stability, exhibiting great potential in wide visible-light applications.

Why and how In composition fluctuations appear in InGaN?

We modeled by kinetic Monte Carlo simulations the growth of InGaN alloys on perfectly oriented and misoriented GaN surfaces. As the growth temperature increases, we show that two phenomena occur: composition pulling along the growth direction and lateral indium rich cluster formation. We show that both phenomena have the same origin, strain, and that temperature enables these phenomena to manifest themselves in measurable quantities. Indeed, there is a continuous transition as a function of growth temperature between statistical alloys, described by a binomial distribution law, and heterogeneous layers with indium rich clusters occurring at higher growth temperatures. We quantify this transition by introducing a cluster index based on the In and Ga atom spatial distribution. We show that this cluster index increases above a given temperature, while at low temperature and, in thin layers, it is determined by surface roughness and the associated In fluctuations. Composition pulling can be observed on a larger temperature range. Composition fluctuations are thus caused by strain, and permitted by In mobility at the surface during growth at sufficiently high temperature.

Two-dimensional confocal photoluminescence spectroscopy of nonpolar a-plane InGaN/GaN multiple quantum wells

A nonplanar a-plane (11–20) and c-plane (0001) InGaN/GaN multiple quantum wells (MQWs) structures were grown an r-plane (1–102) and a c-plane (0001) sapphire (Al2O3) substrate, respectively. Using two-dimensional confocal photoluminescence spectroscopy, the spatially resolved optical characteristics of two samples are examined. We found that the integrated PL intensity of a-plane MQWs is 88.4% greater than that of c-plane MQWs based on our analysis of PL spectra taken at room temperature. According to results from two-dimensional confocal PL mapping, the a-plane MQWs have a more uniform distribution of PL intensity according to two-dimensional space than the c-plane MQWs. Compared to typical c-plane InGaN/GaN MQWs, the experimental results of the two-dimensional confocal PL peak position distribution and PL spectrum skewness map of nonpolar a-plane InGaN/GaN MQWs show increased uniformity of the InGaN alloy in two-dimensional space and a decreased proportion of multiple PL peaks buried in the PL spectrum. These findings are ascribed to higher electron and hole wavefunction overlap caused by decreased the quantum-confinement Stark effect and increased the uniformity of InGaN alloy in the two-dimensional space of nonpolar a-plane InGaN QW.

An Analysis of Mobility Influence in Optoelectronics Parameters in an InGaN/GaN Blue LED

Simulations on mobility influence in optoelectronics parameters from an InGaN/GaN blue LED using the Nextnano++ software arepresented in this paper. These simulations were performed by changing the hole and electron mobility value for the material compounds according to experimental, theoretical, and doping-concentration data already reported in the literature. The power law mobility is used for the current calculation in the quantum drift-diffusion model. The results indicate the lower hole and electron leakage currents correspond to the lowest mobility values for the InGaN alloy, the greatest amount of recombination occurs in the extreme wells within the active layer of the LED and the stable emission is at 3.6 V with peak wavelength λ^LED=456.7 nm and full width at half maximum FWHM~11.1 nm for the three mobilities. Although experimental and theoretical mobility values reach higher carrier density and recombination, the photon emission is broader and unstable. Additionally, the doping-concentration mobility results in lower wavelength shifts and narrows FWHM, making it more stable. The highest quantum efficiency achieved by doping-concentration mobility is only in the breakdown voltage (ηdop−max=60.43%), which is the IQE value comparable to similar LEDs and is more useful for these kinds of semiconductor devices.

Precise determination of deformation potentials in InGaN alloy material in semipolar and nonpolar InGaN quantum wells

Deformation potentials of InGaN have been precisely determined in order to make a reliable prediction of optical gain characteristics in semipolar and nonpolar InGaN quantum wells (QWs) laser didoes (LDs). Since the optical polarization properties in semipolar and nonpolar InGaN QWs are very sensitive to the values of deformation potentials, all the reported data on the optical polarization properties have been theoretically analyzed based on the k · p perturbation theory in this study, and we have made a precise determination of the deformation potentials’ set. In addition, optical gain characteristics of InGaN QWs on GaN substrates with arbitrary substrate orientations have been theoretically calculated by using the determined deformation potentials’ set. It is found that low-angle semipolar substrate orientation (θ ∼ 45°) is very promising for low-cost and high-performance green LDs with cleaved-facet cavity mirrors.

Wigner-Weyl description of light absorption in disordered semiconductor alloys using the localization landscape theory

The presence of disorder in semiconductors can dramatically change their physical properties. Yet, models faithfully accounting for it are still scarce and computationally inefficient. We present a mathematical and computational model able to simulate the optoelectronic response of semiconductor alloys of several tens of nanometer sidelength, while at the same time accounting for the quantum localization effects induced by the compositional disorder at the nano-scale. The model is based on a Wigner-Weyl analysis of the structure of electron and hole eigenstates in phase space made possible by the localization landscape theory. After validation against eigenstates-based computations in 1D and 2D, our model is applied to the computation of light absorption in 3D InGaN alloys of different compositions. We obtain the detailed structures of the absorption tail below the average bandgap and the Urbach energies of all simulated compositions. Moreover, the Wigner-Weyl formalism allows us to define and compute 3D maps of the effective locally absorbed power at all frequencies. Finally the proposed approach opens the way to generalize this method to all energy-exchange processes such as radiative and non-radiative recombination in realistic devices.

Very High Density (>1014 cm−2) Polarization‐Induced 2D Hole Gases Observed in Undoped Pseudomorphic InGaN/AlN Heterostructures

AbstractHigh hole densities are desired in p‐channel field effect transistors to improve the speed and on‐currents. Building on the recently discovered undoped, polarization‐induced GaN/AlN 2D hole gas (2DHG), this work demonstrates the tuning of the piezoelectric polarization difference across the heterointerface by introducing indium in the GaN channel. Using careful design and epitaxial growths, these pseudomorphic (In)GaN/AlN heterostructures result in some of the highest carrier densities of >1014 cm−2 in a III‐nitride heterostructure—just an order below the intrinsic crystal limit of ≈1015 cm−2. These ultra‐high density InGaN/AlN 2DHGs show room temperature mobilities of 0.5–4 cm2 V−1 s−1 and do not freeze out at low temperatures. A characteristic alloy fluctuation energy of 1.0 eV for hole scattering in InGaN alloy is proposed based on the experiments.

Plasma-Assisted Molecular Beam Epitaxy of In-Rich InGaN: Growth Optimization for Near-IR Lasing

Near-infrared stimulated emission (SE) from InGaN layers grown by plasma-assisted molecular beam epitaxy has been studied, and the influence of the growth temperature (T gr) on the SE threshold has been revealed. The obtained experimental data strongly suggest a two-layer model for the grown InGaN structure with a thin defect-rich interface layer and a relatively pure InGaN bulk responsible for light emission. For the latter, the crystalline quality appears to be unaffected by the growth temperature, at least in terms of free electron concentration, which is supported by the similar spontaneous luminescence intensities measured throughout the entire T gr range of 430 °C–510 °C. However, the quality of the interface layer improves with increasing T gr, leading to a decrease in the SE threshold down to ∼10 kW cm−2 at T = 77 K for the samples grown at T gr = 470 °C–480 °C. For the higher growth temperatures (T gr ≥ 490 °C), the SE threshold increases rapidly with T gr, apparently related to the strong waveguide losses due to the increasing surface roughness of the InGaN layer, and SE vanishes completely at T gr = 510 °C, further suppressed by the partial phase separation of the InGaN alloy.

Several processes participating in a decrease and the droop of external quantum efficiency in green InGaN/GaN MQW structures

The obtained experimental results allow us to clarify the nature of mechanisms related to the presence of cations in disordered InGaN alloy and hetero-interfaces. The capture of charge carriers by cations reduces the external quantum efficiency (EQE) in green MQWs at j < 10 A/cm2. The EQE droop phenomenon caused by smoothed out lateral potential fluctuations occurs at j > 10 A/cm2. At j > 40 A/cm2 the droop associated with interactions between charge carriers and dislocations and grain boundaries takes place.

Graphene-Nanorod Enhanced Quasi-Van Der Waals Epitaxy for High Indium Composition Nitride Films.

The nitride films with high indium (In) composition play a crucial role in the fabrication of In-rich InGaN-basedoptoelectronic devices. However, a major limitation is In incorporation requiring a low temperature during growth at the expense of nitride dissociation. Here, to overcome this limitation, a strain-modulated growth method, namely the graphene (Gr)-nanorod (NR) enhanced quasi-van der Waals epitaxy, is proposed to increase the In composition in InGaN alloy. The lattice transparency of Gr enables constraint of in-plane orientation of nitride film and epitaxial relationships at the heterointerface. The Gr interlayer together with NRs buffer layer substantially reduces the stress of the GaN film by 74.4%, from 0.9 to 0.23GPa, and thus increases the In incorporation by 30.7%. The first principles calculations confirm that the release of strain accounts for the dramatic improvement. The photoluminescence peak of multiple quantum wells shifts from 461 to 497nm and the functionally small-sized cyan light-emitting diodes of 7×9mil2 are demonstrated. These findings provide an efficient approach for the growth of In-rich InGaN film and extend the applications of nitrides in advanced optoelectronic, photovoltaic, and thermoelectric devices.

Molecular dynamics simulation of cubic InxGa(1-x)N layers growth by molecular beam epitaxy

The epitaxial growth of cubic InxGa1-xN layers on GaN (001) buffer substrates is investigated using molecular dynamics simulation. The substrate temperature, flux ratio of In, Ga, and N, In concentration, and thermal annealing post-growth were simulated and studied. The dislocation, the critical thickness, and the incorporation of the hexagonal phase into the cubic structure for InxGa1-xN are discussed in detail. Theoretical model conditions were simulated by Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) free-source code; the simulated growths reproduce the experimental thermodynamic conditions for molecular beam epitaxy process during the nucleation and first layers deposited. We consider the Stillinger-Weber In-Ga-N-system potentials. We apply time-and-position-dependent boundary constraints that vary the ensemble treatments of the near-surface solid-phase and the bulk-like regions of the growing layer. The results demonstrate that the simulations are suitable for reproducing the experimental epitaxial growths of cubic phase InGaN alloys with In concentration with 0 < x < 0.5. The hexagonal inclusion is a maximum of 5% for In < 0.2, indicating a preferential pure cubic structure. For In >0.2, the RMS roughness surface increase due to the inclusion of hexagonal planes parallel (110), (111), and (112) in cubic matrix. The average error for cubic phase percentage in the InGaN layers is <1% for x < 0.3, whereas for x = 0.48, the error is 4.8% compared with experimental results.

Comprehensive model toward optimization of SAG In-rich InGaN nanorods by hydride vapor phase epitaxy

Controlled growth of In-rich InGaN nanowires/nanorods (NRs) has long been considered as a very challenging task. Here, we present the first attempt to fabricate InGaN NRs by selective area growth using hydride vapor phase epitaxy. It is shown that InGaN NRs with different indium contents up to 90% can be grown by varying the In/Ga flow ratio. Furthermore, nanowires are observed on the surface of the grown NRs with a density that is proportional to the Ga content. The impact of varying the NH3 partial pressure is investigated to suppress the growth of these nanowires. It is shown that the nanowire density is considerably reduced by increasing the NH3 content in the vapor phase. We attribute the emergence of the nanowires to the final step of growth occurring after stopping the NH3 flow and cooling down the substrate. This is supported by a theoretical model based on the calculation of the supersaturation of the ternary InGaN alloy in interaction with the vapor phase as a function of different parameters assessed at the end of growth. It is shown that the decomposition of the InGaN solid alloy indeed becomes favorable below a critical value of the NH3 partial pressure. The time needed to reach this value increases with increasing the input flow of NH3, and therefore the alloy decomposition leading to the formation of nanowires becomes less effective. These results should be useful for fundamental understanding of the growth of InGaN nanostructures and may help to control their morphology and chemical composition required for device applications.

(Invited) First-Principles Understanding of Deep-Level Defects and Impurities in GaN and Nitride Alloys

The presence of native defects or unwanted impurities can strongly affect semiconductor device performance. Such defects can give rise to deep levels in the band gap, acting as sources of non-radiative recombination, carrier trapping, and sub-band-gap luminescence. Although predicting the properties of deep defects in semiconductors has long been hampered by the band-gap problem of density functional theory (DFT), methodological developments now allow for quantitative predictions. Here we discuss how first-principles calculations have shed light on the role of deep-level defects and impurities in gallium nitride and related alloys.We begin by discussing computational methodologies for calculating the properties of native defects and discuss how to overcome the band-gap problem of DFT. In particular, we examine to what extent calculations performed with semilocal functionals (such as the generalized gradient approximation), combined with correction schemes, can produce accurate results. The properties of vacancy, interstitial, and antisite defects in GaN are discussed, as well as their interactions with impurities such as hydrogen and oxygen. We also discuss first-principles results in the context of experimental observations, and examine how native defects and their complexes impact the performance of nitride devices [1].We also explore how the properties of defects are affected by presence of alloying elements such as indium [2]. With explicit alloy calculations we monitor how defect levels depend on indium content and the distribution of In atoms. The relative shifts of the charge‐state transition levels of different defects are explained by the atomic character of the defect state. Such shifts depend on whether the defect state is composed of valence‐band or conduction‐band states of the host material, or whether it acts as an atomic‐like impurity. Various possible atomic configurations of In and Ga cations in InGaN alloys of given compositions lead to a distribution of charge‐state transition levels. Defects on the nitrogen site lead to a larger spread of defect levels, while defects on the cation site lead to a smaller spread.Finally, we also investigate the properties of heavily C-doped GaN using both optical experiments and hybrid DFT calculations. Previous calculations had established that carbon acceptors (CN) give rise to a yellow luminescence (YL) band near 2.2 eV [3], along with a blue luminescence band near 2.9 eV. Photoluminescence measurements showed these optical transitions shifting as a function of carbon concentration, suggesting a change in the behavior of carbon. With hybrid DFT we calculated the electrical and optical behavior of carbon species containing multiple carbon impurities, which may arise in heavily doped material. We compared the behavior of these complexes to the isolated centers, and find that the CGa-CN complex is a good candidate to explain the shift in the YL peak. Furthermore, we determined the local vibrational modes of carbon impurity centers, and compared these results to recent experiments.[1] J. L. Lyons and C. G. Van de Walle, npj Computational Materials 3, 12 (2017).[2] D. Wickramaratne et al., phys. Stat. sol. (b) 2020 (https://doi.org/10.1002/pssb.201900534).[3] J. L. Lyons, A. Janotti, and C. G. Van de Walle, Phys. Rev. B 89, 035204 (2014).

Experimental studies and model analysis on potential fluctuation in InGaN quantum-well layers

The bandgap energy of InGaN alloy materials can be controlled by changing their alloy composition. Since the compositional fluctuation in the InGaN quantum wells (QWs) greatly affects the characteristics of optical devices, it is very important to understand the electronic structures of such fluctuated InGaN-QW systems for the improvement of their device characteristics. Mobility edge (ME), which is the boundary energy between the localized and delocalized states, can be an index to evaluate the potential fluctuation of carriers. Although several experiments have been proposed to evaluate the ME, they give sometimes different results. In this study, we experimentally and theoretically have studied the evaluation method of ME, and have revealed that the commonly-used evaluation method does not necessarily give accurate results. It is suggested that the method using photoluminescence excitation measurement is the best way to estimate the ME in InGaN-QWs

Structural and functional properties of Zn(Ge,Sn)N2 thin films deposited by reactive sputtering

Semiconductor alloys ZnSnxGe1-xN2 have theoretical crystal structure and electronic structure similar to that of InGaN alloys. These promises of direct and tunable band gaps are very attractive to unlock a suite of functionality for these nitride semiconductors, namely for the use in long wavelength light emitters and light absorbers for solar cells. We report here a structural, electrical and optical investigation of sputtered ZnSnxGe1-xN2 films for 0 ≤ x ≤ 1 by gradually substituting germanium with tin. Compared to InGaN alloys which suffer from a miscibility gap and exhibit phase segregation beyond ~20% In, ZnSnxGe1-xN2 form advantageously a continuous alloy for 0 ≤ x ≤ 1. Its adjustable lattice parameter a (from 3.22 Å to 3.41 Å) according to Vegard's law as well as the linear variation of the vibration modes by Fourier transform infrared spectroscopy indicate that the ZnSnxGe1-xN2 alloying is achievable without phase separation. The single chemical environment measured by Mössbauer spectroscopy for Sn4+ ions, whatever Sn content in ZnSnxGe1-xN2, confirms the continuous nature of alloying. Samples exhibit semiconducting properties, including optical band gaps and electronic behaviors with temperature. The experimental observations show that the resistivity in ZnSnxGe1-xN2 alloys can cover several orders of magnitude from a “quasi-metallic” (for ZnSnN2) to a “quasi-insulating” (for ZnGeN2) behavior and that the band gap is tunable from 2.1 eV to 3.04 eV with a nearly linear dependence on the composition. Thus, ZnSnxGe1-xN2 materials offer a solution for bandgap tunability in nitride semiconductors, and may enable enhanced functionality such as efficient green and red light emitters and light absorbers for photosynthetic devices.

Tuning carrier localization in In-rich InGaN alloys: Correlations between growth kinetics and optical properties

Alloy clustering and consequent carrier localization in InGaN alloys are important aspects with large effect in materials’ optoelectronic properties and related device operation. Their importance is even higher for alloy compositions close to midrange where alloy compositional fluctuations get stronger. Such fluctuations are considered a result of thermodynamic immiscibility and indium segregation to structural defects. However, their dependence on the epitaxial growth process is unknown. Here, we examined the dependence of the degree of resulting carrier localization on growth surface kinetics in InGaN alloys developed by plasma-assisted molecular beam epitaxy. We deposited a large number of alloy thin films, heteroepitaxially on GaN(0001), under different growth temperatures and metallic surface coverage during growth but with similar compositions (∼40%), thicknesses, and growth rates. Their structure was examined by x-ray diffraction. Carrier localization phenomena were investigated employing temperature dependent photoluminescence, while spectroscopic ellipsometry was applied to determine the films’ complex dielectric function. A strong correlation of compositional uniformity and decreased carrier localization with growth conditions that reduce adatoms surface mobility and enhance “out-of-equilibrium” epitaxy character was revealed. This correlation was largely independent of the effects on films' structural properties. Thus, the importance of epitaxial surface kinetic effects on alloy clustering and localization is highlighted. These results are expected to be applicable to the entire alloy composition range and could pave the way for on demand optimal tuning of their optoelectronic properties depending on application requirements.

Deep‐Level Defects and Impurities in InGaN Alloys

In this study, density functional theory calculations with a hybrid functional are used to examine the charge‐state transition levels of native point defects and impurities in InGaN alloys, with the goal of identifying centers that play a role in defect‐assisted recombination. Explicit alloy calculations are used to monitor the dependence of defect levels on indium content and distribution of In atoms. The relative shift (or lack thereof) of the charge‐state transition levels of the different defects is explained by the atomic character of the defect state and whether it is derived from valence‐band or conduction‐band states of the host material or acts as an atomic‐like impurity. The various possible atomic configurations of In and Ga cations for a given composition of InGaN lead to a distribution of charge‐state transition levels. Defects on the nitrogen site lead to a larger spread in levels compared with defects on the cation site.