Tunable strong-field response mediated by deep donor state in V-doped zinc selenide

ConspectusAntimony chalcogenides, including Sb2S3, Sb2Se3 and alloyed Sb2(S,Se)3, have emerged as promising new generation solar cell materials owing to their excellent stability, tunable bandgap in 1.1-1.8 eV, and high extinction coefficient. Different from all the previous solar cell materials, the crystal structures of this class of semiconductors are composed of quasi-one-dimensional ribbons, which renders efficient directional carrier transport along the one-dimensional Sb4(S/Se)6 ribbon. This ribbon structure could generate inert grain boundaries since there is no dangling bond at the side of the ribbons. With these unique properties, it has attracted intense interests in solar cell applications. Over the past decades, device efficiencies have increased from ∼1% to above 11%. The advances in film fabrication, defect passivation and orientation control contribute to the efficiency breakthrough. However, there is still a large gap between current performance and the theoretical efficiency limit of ∼33%. It has been realized that the deep-level point defect plays critical role in increasing the efficiency. In this case, a comprehensive understanding of defect formation and passivation is essential for the fabrication of high quality Sb2(S,Se)3 films for further efficiency breakthrough.Building on the foundational work from our research, this Account presents a unified conceptual framework that traces the defect chemistry of Sb2(S,Se)3 from their quasi-one-dimensional ribbon structures to multidimensional collaborative passivation strategies for device optimization. We first describe how the anion chemical potential and S/Se ratio regulate the formation of vacancies and antisite defects. These factors shape local bonding and lattice strain, which, in turn, influence defect energetics and carrier lifetime. We then examine how controlled chemical modification can adjust short-range coordination environments. Such adjustments refine the electronic structure and can transform harmful deep states into electronically benign ones. We also emphasize strategies that target grain boundaries and surfaces, where deep defects often concentrate due to ribbon termination and structural disorder. Well-designed passivation treatments can reconstruct these regions, reduce under-coordinated atoms, and improve interfacial band alignment. Finally, we discuss recrystallization approaches that promote favorable ribbon orientation and suppress chalcogen loss, a key source of deep donor states. Together, these directions have enabled the power conversion efficiency to exceed 11%. By establishing a unified chemical framework for understanding and controlling point defects, this Account provides guiding principles for advancing Sb2(S,Se)3 materials in terms of sophisticated defect-engineering.

First-principles density functional simulations were employed to investigate the geometries, electrical properties, and hyperfine structures of various beryllium-doped diamond configurations, including interstitial (Bei), substitutional (Bes), and beryllium-nitrogen (Be-N) complexes. The incorporation of Be into the diamond lattice is more favorable as a substitutional dopant than as an interstitial dopant, although both processes are endothermic. Interstitial Be could potentially exhibit motional averaging from planar to axial symmetry with an activation energy of 0.1 eV. The most stable Bes configuration has Td symmetry with a spin state of S = 1. Co-doping with nitrogen reduces the formation energy of Bes-Nn (n = 1–4) complexes, which further decreases as the number of nitrogen atoms increases. This is attributed to the smaller covalent radius of nitrogen compared to carbon, resulting in reduced lattice distortion. Bes-N3 and Bes-N4 co-doping introduces shallow donors, while Bes exhibits n-type semiconductivity, but the deep donor level renders it impractical for room-temperature applications. These findings provide valuable insights into the behavior of beryllium as a dopant in diamond and highlight the potential of beryllium-nitrogen co-doping for achieving n-type diamond semiconductors.

Oxygen vacancies are regarded as crucial defects greatly affecting the electronic and optical properties of oxide films and devices, yet systematic studies on κ-Ga2O3 are still lacking. Herein, we investigate the thermodynamic, electronic, and optical properties of oxygen vacancies in κ-Ga2O3 using density functional theory calculations with the hybrid functional. The electronic structure reveals that oxygen vacancies create a deep donor defect in the bandgap, with defect levels and transition energies influenced by Ga atom displacement and localized electron dynamics. This interplay explains the stability of vacancies at specific sites and their connection to experimentally observed defect levels. Additionally, oxygen vacancies generate distinct absorption and electron energy loss peaks in the ultraviolet range. Our results elucidate the nature of oxygen vacancies, and offering a foundation for tuning and optimizing the electrical and optical properties of κ-Ga2O3 films and improving device performance through defect engineering.

With the largest tunable bandgap in the III-N class of semiconductors (6.02eV) and high thermal conductivity, aluminum nitride (AlN) has immense potential for use in high power electronics, heat sinks, and UV detectors. N-type doping of molecular beam epitaxy (MBE) and metal organic chemical vapor deposition (MOCVD) heteroepitaxially grown AlN is typically achieved with Si, a donor in AlN, with a typical ionization energy of approximately 300 meV1.AlN wafers and homoepitaxially grown films consisting of AlN on SiC from different vendors of N- and Al- polarities were measured using Raman spectroscopy and photoluminescence (PL) to better understand the underlying stress and defect bands present. An increasing E2 (high) shift in the Raman data was observed for each of the N-polar samples, though not in the Al-polar samples. This shift was found to be less than one wavenumber across a 2” wafer length from the center to the edge, but was consistent, suggesting existing tensile stress on the central region of the wafer, with decreasing tensile stress towards the edge. PL defect bands of interest include (i) one centered near 2.40eV (516 nm), corresponding to the presence of nitrogen vacancies (VN), (ii) one in the UV region centered around 3.6eV (344 nm) corresponding to oxygen substitution (ON)2 ,(iii) one near 3.0eV (413 nm) representing a secondary defect complex of VAl-ON or VAl-SiAl , potentially significant in helping to measure doping efficiency2, and finally, (iv) a band centered near 2.8eV (443 nm) points to a radiative recombination of highly charged aluminum vacancies (VAl)3-/2- and the valence band, giving rise to a visible orange luminescence3. X-ray diffraction (XRD) was used to look at the crystal quality of the samples tested, atomic force microscopy (AFM) was used to measure surface morphology and Young’s modulus, and optical profilometry was used to investigate the surface topography of the samples on a larger length scale than AFM.To study n-type doping efficiency in AlN, 400nm Si-doped films were grown. Due to the presence of large defect bands in the bulk material and the deep donor level of the Si, many dopants are not ionized and instead become deep acceptors. This leads to a significant reduction in the number of freely ionized carriers in the material, diminishing the potential electrical properties of the material. To solve this issue, the temperature of the sample is increased, which increases the number of ionized carriers, and moves the operational mode closer to the intrinsic region. Temperature dependent Hall effect studies of Al- and N-polar substrates were investigated in this work with regards to carrier concentration and doping efficiency, whose results can then be extrapolated to lower temperatures. Capacitance-voltage (C-V) testing was performed to further characterize the interface trap states, carrier lifetimes, and doping, while the transmission line model (TLM) was used to measure the impact of defects on metal-semiconductor contact resistivity. In this work, doping efficiency, defect structures, and electrical transport properties in AlN were characterized, with an eye on enhancing its electrical performance and practical applications.

Understanding the effects of native oxygen vacancy (VO) and gallium vacancy (VGa) in two-dimensional (2D) Ga2O3semiconductors is critical for optimizing device efficiency and developing innovative applications. In this work, the structural stability, electronic structure, carrier mobility and conductivity of thickness-dependent 2D Ga2O3induced by native VOand VGaare systematically studied. In Ga2O3VOconfiguration, the newly occupied mid-gap states primarily composed of O-2p, Ga-3p, and Ga-3d orbitals are formed, demonstrating a deep donor feature. The created impurity levels lower the bandgaps of monolayer, bilayer, and trilayer Ga2O3VOto 1.60, 1.64, and 1.53 eV, respectively. The electron mobility exhibits a high value up to ∼12 154.89 cm2V-1s-1in bilayer Ga2O3VO. Shallow acceptor states primarily composed of O-2p and Ga-3d orbitals are introduced for Ga2O3VGaconfiguration, suggesting the effective p-type doping behavior. The bandgaps of monolayer, bilayer, and trilayer Ga2O3VGaare of respectively 2.31, 1.90, and 1.84 eV, accompanying with the monotonous decreasing of hole mobilities from 261.46-85.75 cm2V-1s-1alongx-direction. Meanwhile, the thickness dependent n-type and p-type conductivities are endowed with the similar trends as those of carrier mobilities. Distinct dimensional induced band features and transport properties have been resolved in VOand VGacases. The high carrier mobility and strong anisotropic observed in vacancy-deficient 2D Ga2O3highlight the insights into defect engineering strategies for next-generation wide-bandgap semiconductors.

Abstract We investigate the formation and characteristics of vacancy clusters (VCs) in gallium nitride (GaN) grown by metal–organic chemical vapor deposition. The research identifies vacancy-type defects, particularly V Ga –H i complexes, using positron annihilation spectroscopy, in as-grown sample which are transformed into VCs 2V Ga –2V N during low-energy electron beam irradiation. The study employs photoluminescence and cathodoluminescence spectroscopy to analyze the luminescence properties, demonstrating that yellow band and excitonic near-band-edge emission are greatly enhanced during the VC process. The results indicate that the luminescence spectra of the samples change significantly during electron beam irradiation, highlighting the dynamic behavior of defects in GaN under different conditions. The dominant change affecting the luminescence properties seems to be the elimination of a deep donor acting like a non-radiative centrum. The experimental evidence suggests that this deep donor is V N . The findings contribute to a deeper understanding of the role of nitrogen vacancy, vacancy complexes and clusters in GaN, which is crucial for optimizing its applications in optoelectronic devices and their processing.

Aluminum nitride (AlN) has attracted considerable attention for its promising applications in short-wavelength optoelectronic devices. However, undesirable blue and violet luminescence from MOCVD-grown AlN films has impeded their development. This study has experimentally investigated the blue luminescence at 2.7 eV originated from the donor-acceptor pair (DAP) transitions between VAl acceptor and deep donors, and the violet luminescence at 3.0eVoriginated from the transitions between Al(NOy)x complex and conduction band or shallow donor level. Additionally, incorporating a small amount of Ga into the AlN layer during the growth can modulate the defect types and suppress violet luminescence. This study is crucial for improving the performance of AlN-based optoelectronic devices.

Abstract AlGaN nanowires are promising for deep ultraviolet optoelectronic applications, but their performance is significantly affected by defects, and the mechanism of defect regulation remains unclear. In this work, the effect of vacancy and interstitial defects on the stability, structural and electronic properties of AlGaN nanowires are systematically investigated via first-principles. Our results demonstrate that the N vacancy exhibits the lowest formation energy of 3.68 eV, indicating that it is the most thermodynamically favorable defect type in AlGaN nanowires. Besides, as the defect position migrates from the center to the surface layer of nanowires, the stability of N vacancy gradually decreases (formation energy increases from 3.68 eV to 4.56 eV), while that of Ga vacancy progressively enhances (formation energy decreases from 8.06 eV to 7.88 eV). In addition, the introduction of defects induces significant relaxation in the atomic structure, with bond length variations up to 4.35% ∼ 7.50% for Ga-Ga around N vacancy and 9.92% ∼ 13.95% for N-N around Ga vacancy. Despite the incorporation of point defects, AlGaN nanowires preserve the direct bandgap characteristic. Moreover, Al vacancy, Ga vacancy and N interstitial introduce shallow acceptor levels at 0.12 ∼ 0.37 eV above the valence band maximum, while N vacancy, Ga interstitial and Al interstitial induce deep donor levels at 0.42 ∼ 1.58 eV below the conduction band minimum. Furthermore, Mulliken charge calculations reveal that atomic charge alterations induced by defects mainly occur within the neighboring coordination shell, verifying the localized nature of defect effects.

Ultrawide bandgap AlN is a highly attractive material for power and radio frequency electronics. Unipolar n-AlN Schottky barrier diodes have demonstrated their strengths, whereas further development of AlN-based bipolar devices is desired but lacked. In this letter, we report single-crystalline p-Si/n-AlN p-n diodes (PNDs) with superior performance, accomplished by grafting a p-type Si nanomembrane onto an n-AlN film. Improved Ohmic contact directly on n-AlN was obtained through high temperature annealing at 1100 °C with contact resistivity of 4.9×10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> Ω cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>. The PNDs exhibited remarkable uniformity across the wafer, excellent rectifying characteristics with a high ratio of ~3×10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> at ±10 V, low leakage current density of ~6.25×10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-9</sup> A/cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at -10 V, and hysteresis-free operation from -10 V to 30 V. Furthermore, the devices demonstrated superior thermal stability, with the on-resistance decreasing from 15.8 to 0.33 Ωcm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> as temperature increased from room temperature to 100 °C, revealing an activation energy of ~425 meV for deep donor state in AlN. No destructive breakdown of the devices was observed up to –894 V. These results highlight the Si/AlN PNDs’ potential for development of AlN-based electronic devices.

Abstract A consistent increase in conductance in La‐doped BaSnO 3 (BLSO) is observed after forming an interface with the non‐polar perovskite SrHfO 3 (SHO). The conductance enhancement at the SHO/BLSO interface is measured as a function of the thickness of the SHO layer and the La doping rate in the BLSO layer. A monotonic increase of conductance as a function of the SHO thickness is observed, unlike the case of polar interfaces of LaInO 3 /BaSnO 3 and LaScO 3 /BaSnO 3 . The first several unit cells of SHO have the most significant impact on conductance. It is also found that the SHO/BLSO interface requires little doping (≈0.2%) to compensate for the deep acceptors in BaSnO 3 . To determine the charge carrier distribution, capacitance–voltage profiling is employed, which indicates that the charge carriers are confined within 1–2 nm of the interface. The observed 2D electron gas behavior at the interface is analyzed using a self‐consistent Poisson‐Schrödinger equation solver. This analysis provides a consistent picture of the SHO thickness and the La‐doping dependence of conductance enhancement at the SHO/BLSO interface, suggesting that the large conduction band offset at the SHO/BLSO interface and the intrinsic deep donor states in SHO are responsible for formation of a potential well in the BLSO side.

Abstract Oxygen vacancies are regarded as crucial defects greatly affecting the electronic and optical properties of oxide films and devices, yet systematic studies on k-Ga2O3 are still lacking. Herein, we investigate the thermodynamic, electronic, and optical properties of oxygen vacancies in k-Ga2O3 using density functional theory calculations with the hybrid functional. The electronic structure reveals that oxygen vacancies create a deep donor defect in the bandgap, with defect levels and transition energies influenced by Ga atom displacement and localized electron dynamics. This correlation links the stability of oxygen vacancies at specific sites and the contribution of oxygen orbitals to charge density at the valence band maximum with the microscopic origins of experimental defect levels in oxygen vacancy states. Oxygen defects give rise to additional peaks in the lower energy ultraviolet regions of the absorption and electron energy loss spectra, consistent with earlier experimental studies. Our results elucidate the nature of oxygen vacancies, and offering a foundation for tuning and optimizing the electrical and optical properties of κ-Ga2O3 films and improving device performance through defect engineering.

We investigated the origin of electrical degradation in ion implantation doping and discussed the lowest limit of doping concentration. In this study, we particularly performed the light B doping of acceptor boron from 1016 to 1017 cm−3 concentrations by ion implantation to clarify the influence of defects induced by ion bombardment to electrical properties. The electrical properties were analyzed by Hall effect measurement compared to theoretical calculations strictly dealing with charge compensation effects. As a result, we clearly observed excellent p-type conduction and an ionization energy of 0.38 eV. The sample with a doping concentration of 2.7 × 1017 cm−3 showed the smallest compensation ratio and the highest mobility of 510 cm2 V−1 s−1 at 300 K. This is the highest value among the previous reports in the Hall mobility observed for B-doped diamond by ion implantation, but still only half of the ideally expected value. On the other hand, the lightly doped diamond with less than 1017 cm−3 concentrations also showed p-type conductivity but a significantly high compensation ratio, and we found a compensating deep donor level at 0.90 eV measured from valence band maximum. Compared to the previous theoretical calculation, it can be the substitutional B and vacancy complex. The compensating donor concentration gradually increased with increasing doping concentration, suggesting that the donor-like centers induced by the doping process with ion implantation probably affect the carrier transport. Fixed space charge generated by acceptor compensation was found to be the most primary factor determining the upper limit of mobility in ion implantation doping.

Abstract The charging effect of deep-level defects (DLD) in GaN based power high electron mobility transistors (HEMTs) on Si substrate is one of the reasons for their conductance stability issues during the switching loop, yet a comprehensive understanding of their behaviors on channel conductance is still lacking. In this study, in addition to the acceptor DLD resulted from the carbon doping, a donor-like DLD was observed with its energy level, and its physical location in the AlGaN/GaN HEMT epi-structure was also confirmed by using channel transient current measurement under the negative substrate bias condition. By the assistance of finite element numerical simulation, the transient current behavior was believed to be decided by the ionizing competition process between the deep donor and deep acceptor under the substrate bias induced electric field, which is due to the differences in density, ionization energy, and the ionizing time constant of both donor- and acceptor-DLD.

We show with hybrid density functional theory calculations that chalcogen donors other than oxygen (i.e. SN, SeN, and TeN) give rise to deep donor states in aluminum nitride. These donors trap a localized electron in their neutral charge state, leading to deep (+/0) donor levels that are 0.45 eV or more from the conduction-band edge. As such, this behavior is distinct from theDXbehavior leads to deep (+/-) levels which affects other donors such as ONand SiAl. We highlight how these results hint at the formation of small electron polarons in AlN, which are found to be unstable in the bulk, but metastable when bound to donor dopants like SiAland the chalocogens, with activation energies on the order of 0.2-0.3 eV. These results indicate that S, Se, and Te are not shallow donor dopants in aluminum nitride and identify origins of the experimentally observed ∼200-300 meV activation energies for dopant activation in donor-doped samples.

Abstract To improve the blocking capability of U-shaped trench gate MOSFETs (UMOSFETs) based on nitrogen-implanted current blocking layer (CBL), the post-implantation annealing atmosphere is optimized. Compared to the UMOSFET annealed in nitrogen, the oxygen-annealed device shows an improved breakdown voltage, increasing from 830 V to 1330 V, while maintaining similar specific on-resistance. By analyzing the leakage mechanisms of CBLs, the lower leakage current in the oxygen-annealed device is attributed to the reduced concentration of certain deep donors and the change in trap energy level involved in the Poole–Frenkel (PF) emission. This work validates oxygen annealing as an effective approach to optimizing nitrogen-implanted β-Ga2O3 power MOSFETs.

Radiative transitions in MgAl 2 O 4 spinel single crystal were investigated after irradiation with He + ions of fluence ∼10 17 particles/cm 2 . Photoluminescence (PL), PL excitation spectra and PL decay curves were measured at cryogenic temperatures of 8 K. It is shown that PL decay kinetics of 5 eV (250 nm) and 3 eV (420 nm) bands are similar because of the common excited state. Furthermore, after irradiation PL band at ∼5 eV preserved characteristic behaviour of the donor-acceptor pair transitions. The PL channels involve electronic transitions of antisite defects, Mg Al (shallow acceptor) and Al Mg (shallow donor), and oxygen vacancy V O (deep donor), while Al Mg served an intermediate of the electronic excitation channel. The intense emissions were assigned to V O • ∗ → V O • (3 eV) and V O • ∗ → Mg Al × (5 eV), which involve respectively energy and energy-electron transfer. Participation of the doubly-ionized oxygen vacancy V O •• in the energy/electron transfer is suggested. The obtained data enabled a generalised scheme of electronic transitions in MgAl 2 O 4 spinel in presence of intrinsic defects. • Low-temperature photoluminescence (PL) of MgAl 2 O 4 spinel crystal was analyzed. • Single-ionized oxygen vacancy (F + ) is common excited state of PL at 5 and 3 eV. • PL of irradiated MgAl 2 O 4 involves defect clusters containing oxygen vacancies. • Scheme of radiative transitions in MgAl 2 O 4 with intrinsic defects is proposed.

In this study, zinc oxide (ZnO) and copper-doped zinc oxide nanoparticles (Cu-ZnO NPs) were synthesized using a green method that employed Rosmarinus officinalis leaf extract as a reducing agent. Copper was incorporated as a dopant at concentrations of 3% and 5%. Zinc acetate dihydrate and copper acetate served as the precursors and dopants, respectively. The synthesized samples were characterized utilizing a range of techniques, including XRD, SEM, EDX, Raman spectroscopy, UV-visible spectroscopy, and PL spectroscopy. XRD and Raman spectroscopy analyses validated the effective incorporation of Cu²⁺ ions into the ZnO wurtzite structure. SEM analysis indicated that the nanoparticles displayed a spherical morphology, while EDX analysis confirmed the presence of zinc (Zn), copper (Cu), and oxygen (O), thereby validating the sample's purity. UV-visible spectra revealed a reduction in the optical band gap with increasing Cu concentration. Photoluminescence peaks observed at 383 nm and 565 nm were ascribed to electron transitions from deep donor levels, particularly from Zn interstitials to Zn and oxygen vacancies. The 5% Cu-doped ZnO NPs demonstrated the highest photocatalytic activity, achieving 90% degradation of Rhodamine B (RhB) dye under UV irradiation in 135 minutes. They also exhibited significant antibacterial activity, particularly against Gram-positive bacteria (Staphylococcus aureus) compared to Gram-negative bacteria (Escherichia coli).

The “photo‐gain effect” amplifying the DC photocurrent of κ‐Ga 2 O 3 UV‐C photoresistors is analyzed by means of 2D numerical simulations and linked to the capture of photogenerated holes by deep donor levels, probably associated with oxygen vacancies. The resulting ionization of the deep donors leads to an increase in the electron density, hence to enhanced conductivity under illumination.

Bismuth has been investigated as a potential n-type dopant in hybrid lead halide perovskites, but its behavior in all-inorganic perovskites such as CsPbBr3 has not been thoroughly characterized. We show that Bi behaves as a deep defect in CsPbBr3 and gives rise to broad near-infrared emission, similar to its behavior in hybrid perovskites, but a phenomenon not previously reported in CsPbBr3. Using inverse temperature crystallization, we synthesized a series of Bi-doped CsPbBr3 crystals and quantified their Bi concentrations by inductively coupled plasma optical emission spectroscopy. Bi incorporation redshifted the absorption edge, and hybrid density functional theory calculations show that this increased absorption comes from excitation into the deep donor level of Bi, not from narrowing of the bandgap of CsPbBr3. All Bi-doped crystals emitted both narrow band-edge (2.37 eV) and broad defect-level (1.16 eV) photoluminescence, consistent with our theoretical prediction. Time-resolved photoluminescence measurements indicate that Bi incorporation decreases the lifetime of the band-edge emission and gives rise to long-lived defect emission. Power-dependent photoluminescence measurements conducted at 14 K show that the band-edge peak intensity scales as expected for a free or bound exciton, while the sublinear scaling of the infrared defect peak is consistent with recombination between a free hole and a trapped electron, as proposed by theory. These results demonstrate the quantitative accuracy with which current theoretical approaches predict defect behavior in halide perovskites; such theory is key to guiding the experimental development of doping in these materials.