Achieving efficient p-type conductivity is essential for advancing diamond-based high-power and high-frequency electronic devices. In this study, we employ first-principles calculation to evaluate Be as a p-type dopant in diamond and investigate the synergistic enhancement achieved through N-Be co-doping. The high-concentration Be doping can significantly reduce the acceptor ionization energy to 0.35 eV. More importantly, N-Be co-doping substantially reduces defect formation energies and acceptor ionization energies, N-4Be co-doped structure shows the reduced formation energy of 3.37 eV and acceptor ionization energy as low as 0.30 eV. These findings pave the way for the experimental realization of high-performance diamond-based electronic devices and suggest the potential for exploring donor–acceptor co-doping to achieve efficient p-type conductivity.

There is a growing interest in the recent years toward developing wide gap semiconductor nanostructures, and a lot of efforts have been dedicated to ZnO. In order to design core shell structures, a larger bandgap material is needed, which would ideally be similarly environment friendly. ZnS is an interesting possibility and although some efforts were devoted to it in the literature, its properties are not yet fully understood and precisely measured. In this work, we make a thorough analysis of high quality ZnS epilayers, in order to precisely determine the basic optical properties related to excitons and impurities in ZnS. We have made the first precise quantitative determination of residual strain using high-resolution x-ray diffraction. This allows us to demonstrate that, as it was hypothesized in most previous works, thermoelastic strain originating from the layer-substrate expansion coefficient mismatch is responsible for shifts and splitting of exciton photoluminescence lines. The identification of the bound excitons’ optical transitions is analyzed through their temperature/power dependence, in order to precisely assess their exact nature. Combined with the careful determination of donor and acceptor ionization energies in our ZnS sample, we discard the possibility of sodium as the main residual acceptor, as it has often been proposed in the literature.

As the first discovered p-type transparent conductive material, copper(I) iodide (CuI) is considered the most competitive p-type candidate in the field of transparent electronics. Herein, we introduced a low-temperature buffer-layer-assisted strategy to grow γ-CuI with significantly improved structural quality and electrical transport properties by pulsed laser deposition. By adjusting the growth temperature, we can manipulate the rotation domain structure, control the hole concentration Nh from 1014 to 1019 cm−3, and achieve mobility μh = 25 cm2 V−1 s−1 being similar to that of bulk CuI. Based on the temperature-dependent Hall-effect measurement, the ionization energy of a shallow acceptor of EI,S = 137 ± 8 meV and that of a deeper acceptor of EI,D = 262 ± 23 meV were determined. This grown strategy not only enables high-quality CuI film preparation, but also to tailor their electrical properties for integration with n-type semiconductors in transparent electronic circuits.

Deep ultraviolet light-emitting diodes (DUV-LEDs) are hindered by optical losses and high operating voltages, primarily due to p-contact layers such as light absorption in p-GaN or high operating voltages linked to inferior hole injection caused by high acceptor ionization energy for p-AlGaN and large bulk resistance in AlGaN-based tunneling junctions (TJs). To overcome these challenges, we introduce a transparent AlGaN polarized ultrathin tunneling junction (PUTJ). This innovative design features a low-bulk-resistance TJ with ultrathin p- and n-regions (20 nm), incorporating an intrinsic AlGaN interlayer that leverages polarized electric fields to enhance the interband tunneling injection of holes. Benefiting from the significantly reduced TJ thickness, the 273 nm PUTJ DUV-LED achieves minimal absorption losses and a record-low operating voltage of 5.8 V at 30 A/cm2. This advancement represents a substantial leap forward in the development of efficient DUV light sources, potentially revolutionizing III-nitride optoelectronics with reduced optical and electrical losses at the p-contact layer.

Relationship between the hole concentration at room temperature and the Mg doping concentration in p-GaN grown by MOCVD after sufficient annealing was studied in this paper. Different annealing conditions were applied to obtain sufficient activation for p-GaN samples with different Mg doping ranges. Hole concentration, resistivity and mobility were characterized by room-temperature Hall measurements. The Mg doping concentration and the residual impurities such as H, C, O and Si were measured by secondary ion mass spectroscopy, confirming negligible compensations by the impurities. The hole concentration, resistivity and mobility data are presented as a function of Mg concentration, and are compared with literature data. The appropriate curve relating the Mg doping concentration to the hole concentration is derived using a charge neutrality equation and the ionized-acceptor-density [ ] (cm−3) dependent ionization energy of Mg acceptor was determined as = 184 − 2.66 × 10−5 × [ ]1/3 meV.

Recently, LiGa5O8 was claimed to be a p-type dopable ultrawide-bandgap oxide, based on measurements of undoped material. Here, the electronic properties of potential acceptor dopant impurities in LiGa5O8 are calculated using hybrid density functional theory to evaluate their potential for causing p-type conductivity. As with the related compound LiGaO2, the heavy oxygen-derived valence bands lead to stable self-trapped holes in LiGa5O8. Acceptor defects and dopants also bind trapped holes (or small polarons), which lead to large acceptor ionization energies. The calculations here indicate that neither native acceptor defects (such as cation vacancies or antisites) nor impurity dopants can give rise to p-type conductivity in LiGa5O8. Optical transitions associated with these defects are also calculated, in order to allow for possible experimental verification of their behavior.

A major shortcoming of ultrawide-bandgap (UWBG) semiconductors is unipolar doping, in which either n-type or p-type conductivity is typically possible, but not both within the same material. For UWBG oxides, the issue is usually the p-type conductivity, which is inhibited by a strong tendency to form self-trapped holes (small polarons) in the material. Recently, rutile germanium oxide (r-GeO2), with a band gap near 4.7 eV, was identified as a material that might break this paradigm. However, the predicted acceptor ionization energies are still relatively high (∼0.4 eV), limiting p-type conductivity. To assess whether r-GeO2 is an outlier due to its crystal structure, the properties of a set of rutile oxides are calculated and compared. Hybrid density functional calculations indicate that rutile TiO2 and SnO2 strongly trap holes at acceptor impurities, consistent with previous work. Self-trapped holes are found to be unstable in r-SiO2, a metastable polymorph that has a band gap near 8.5 eV. Group-III acceptor ionization energies are also found to be lowest among the rutile oxides and approach those of GaN. Acceptor impurities have sufficiently low formation energies to not be compensated by donors such as oxygen vacancies, at least under O-rich limit conditions. Based on the results, it appears that r-SiO2 has the potential to exhibit the most efficient p-type conductivity when compared to other UWBG oxides.

The high acceptor ionization energy and, thus, low carrier concentration in p-type III-nitride have widely been recognized as the bottleneck preventing the development of high-efficiency light-emitting-diodes (LEDs). In this contribution, the influences of 193 nm pulsed laser annealing on the structure, electrical, and optical properties of p-type GaN were systematically analyzed. The hole concentration of p-GaN first increases and then decreases with increasing laser fluence, regardless of post-growth thermal annealing. The effective dopant activation due to laser annealing can be attributed to the dissociation of Mg–H complexes during the treatment. Laser-annealed p-GaN was utilized in a 280 nm deep ultraviolet LED. A maximum of 1.47 times higher wall-plug-efficiency enhancement factor was obtained compared to that without laser annealing, demonstrating that 193 nm laser annealing plays a decisive role in the boosting of quantum efficiency of optoelectronic devices.

A theoretical explanation is proposed for the shape of the long-wavelength edge of the luminescence line, which is caused by the recombination of a free electron and a hole of a neutral acceptor. The formation of complexes, in which a single hole is localized by the field of two attracting ions (\(A_{2}^{ - }\) complexes) and the subsequent recombination of holes in such complexes with electrons of the conduction band are considered. The Coulomb repulsion in the final state after recombination and the dispersion of the complexes in terms of the interionic distance provide an extended long-wavelength tail of the luminescence line, comparable in magnitude to the ionization energy of a single acceptor.

The ionization energy (IE) offset of a donor–acceptor pair provides the driving force for hole transfer and subsequent free charge carrier generation in low‐bandgap nonfullerene organic solar cells (OSCs). However, the interfacial energetic landscape in bulk heterojunction OSCs is determined by the materials’ electronic structure and intermolecular interactions at the donor/acceptor interface, causing local energy‐level shifts and disorder. Herein, the impact of the IE offset on the charge transfer efficiency and charge carrier dynamics is systematically evaluated by characterizing PM6/ITIC, PM6/IT‐2Cl, and PM6/IT‐4Cl planar heterojunction (PHJ) solar cells. Ultrafast spectroscopy and time‐resolved charge carrier density measurements reveal that an IE offset of about ≈0.5 eV leads to efficient hole transfer and subsequent free charge generation. Furthermore, bimolecular charge recombination and consequently triplet generation are significantly reduced in systems with high IE offset. This work underlines the importance of sizeable donor–acceptor IE offsets in PHJ nonfullerene OSCs as critical for high‐efficiency donor/acceptor material and device design.

Compositions and properties of high-conductivity nitrogen-doped p-type β-Ga2O3 films prepared by the thermal oxidation of GaN in N2O ambient

This work investigates the suppression and compensation effect of oxygen on the behaviors and characteristics of heavily boron-doped microwave plasma chemical vapor deposition (MPCVD) diamond films. The suppression effect of oxygen on boron incorporation is observed by an improvement in crystal quality when oxygen is added during the diamond doping process. A relatively low hole concentration is expected and verified by Hall effect measurements due to the compensation effect of oxygen as a deep donor in diamond. A low acceptor concentration, high compensation donor concentration and relatively larger acceptor ionization energy are then induced by the incorporation of oxygen; however, a heavily boron-doped diamond film with high crystal quality can also be expected. The formation of an oxygen–boron complex structure instead of oxygen substitution, as indicated by the results of x-ray photoelectron spectroscopy, is suggested to be more responsible for the observed enhanced compensation effect due to its predicted low formation energy. Meanwhile, density functional theory calculations show that the boron–oxygen complex structure is easily formed in diamond with a formation energy of –0.83 eV. This work provides a comprehensive understanding of oxygen compensation in heavily boron-doped diamond.

Although Ga2O3 is widely believed to be the among most promising ultrawide-bandgap semiconductors, its inability to be p-type doped hampers future applications. Moreover, alloying with aluminum increases the Ga2O3 band gap, but it is unclear if electrical conductivity of AlGO alloys can be controlled. The properties of group-IV (C, Si, Ge, and Sn) and transition metal (Hf, Zr, and Ta) substitutional dopants in AlGO alloys are systematically explored here using first-principles hybrid functional calculations. In Ga2O3, all dopants act as shallow donors. However, in Al2O3 all are deep defects, characterized by DX behavior or the emergence of positive-U (+/0) levels. Combining our calculations of dopant charge-state transition levels with information of the AlGO alloy band structure, the critical Al composition at which each dopant transitions from being a shallow to a deep donor is estimated. Si is identified as being the most efficient dopant to achieve n-type conductivity in high Al-content AlGO alloys, acting as a shallow donor over the entire predicted stability range for AlGO solid solutions. Compensation by other unintentional impurities (such as H and C) is also assessed.Other oxide materials have also emerged as potential competitors to Ga2O3, but their propensity for hole conductivity is less well known. Here the stability of hole polarons in a set of ultrawide-bandgap oxides (Ga2O3, Al2O3, ZnGa2O4, MgGa2O4, LiGaO2 and GeO2) is examined and compared, both in pristine material and in the presence of acceptor impurities. Holes spontaneously self-trap in all oxides investigated, with varying stabilities. Acceptor impurities further stabilize these trapped holes, leading to large acceptor ionization energies. Hole trapping also leads to characteristic distortions and distinct optical transitions, which may explain some experimentally-observed signals. These results indicate that achieving p-type conductivity in any of these oxides is unlikely, with the possible exception of GeO2.This work was performed in collaboration with Darshana Wickramaratne (NRL), Joel Varley (LLNL), Sai Mu (UCSB), Mengen Wang (UCSB) and Chris Van de Walle (UCSB), and was supported by the ONR/NRL 6.1 Basic Research Program.

MeV level aluminum implants into 4H-SiC were performed as part of superjunction diode fabrication. Measurement of resistance test structures produced resistivities well above expected values with large decreases at elevated temperatures. Capacitance-voltage measurements indicate a high activation rate of the implanted aluminum. Temperature dependent Hall measurements produce reasonable hole mobilities with acceptor ionization energies of approximately 330meV, well above the 200meV expected for low concentration aluminum doping in 4H-SiC.

Although Ga2O3 is widely believed to be one of the most promising ultrawide-bandgap semiconductors, its inability to be p-type doped hampers its future applications. Other oxides have recently emerged as potential competitors to Ga2O3, but their propensity for hole conductivity is less well known. Here, the stability of hole polarons is examined in pristine material and in the presence of impurities for a set of ultrawide-bandgap oxides (Ga2O3, Al2O3, ZnGa2O4, MgGa2O4, LiGaO2, and GeO2). Holes spontaneously self trap in all oxides investigated here. Acceptor impurities (such as group-I elements, N, and F) further stabilize these trapped holes, leading to large acceptor ionization energies. Hole trapping also leads to characteristic distortions and distinct optical transitions, which may explain some experimentally observed signals. These results indicate that achieving p-type conductivity in any of these oxides is unlikely, with the possible exception of GeO2.

Abstract The role of two defects in the ambipolar character of nanocrystalline selenium poor Sb2Se3 is studied. At low temperature, the electrical transport in Sb2Se3 thin films with nm‐sized crystallites and grains is dominated by the ionization of a shallow acceptor, while at high temperature a deep donor is the leading one. The ionization energy of the deep donor agrees with theoretical reports for selenium vacancies. However, the value of the ionization energy of the shallow acceptor is in contradiction with theoretical reports pointing out to an unreported shallow defect. These findings have been confirmed by two independent experimental techniques, Electron Paramagnetic Resonance, and electrical transport as a function of temperature. The mobility of the free carriers has been found not to be limited by grain potential barriers (GPB), in contrast with polycrystalline thin films. Both findings, new shallow acceptor and zero height GPB, constitute advantages for the design of nanostructured Sb2Se3‐based solar cells and other optoelectronic devices. These results not only provide useful information for the growth of nanocrystalline Sb2Se3 thin films with ambipolar transport properties, but also about the complexity of defect physics in low‐symmetry and Q1D semiconductors.

Positive and negative charge trapping GaN HEMTs: Interplay between thermal emission and transport-limited processes

Efficient p-type doping of III-nitride materials is notoriously difficult due to their large bandgaps, intrinsic n-type doping, and the large ionization energy of acceptors. Specifically, aluminum-containing nitrides such as AlN and AlGaN have demonstrated low p-type conductivity, which increases device resistances and reduces carrier injection in optoelectronic applications. Dilute-anion III-nitride materials are a promising solution for addressing this issue and increasing the activation efficiency of p-type dopants. The upward movement of the valence bands in these materials reduces the ionization energy of the dopants, allowing for enhanced p-type conductivity in comparison to the conventional nitrides. Incorporation of a dilute-arsenic impurity into AlN is hypothesized to significantly reduce the ionization energy of Mg-acceptors from 500 meV to 286 meV, allowing for a two-order magnitude increase in activation efficiency in 6.25%-As AlNAs over that of AlN.

Energy-driven multi-step structural phase transition mechanism to achieve high-quality p-type nitrogen-doped β-Ga2O3 films

Due to the large ionization energy of Mg acceptors in GaN, dynamic punch-through will occur in vertical GaN MOSFETs. To avoid this, higher doping and/or a thicker p-body region should be utilized. However, this increases the channel resistance. In this letter, we suggest that the Poole–Frenkel (P–F) effect has significant impact on dynamic punch-through because of the high electric field in the depletion region under a large bias voltage. Systematic TCAD simulations of simplified vertical GaN MOSFET structures were carried out. We show that the device design considering the P–F effect results in a reduction in the increase in channel resistance.