Deep Donor Level Research Articles

First principles investigation on the Boron‐VA (VA=N, P, As, Sb) complexes in diamond for possible n-type conductivity

The possibility of group VA mono-doping and B-VA (VA=N, P, As, Sb) co-doping impurities being effective shallow donors in diamond is explored through first principles calculations. It is found that the solubility of VA atoms in diamond can be improved by the introduction of B atom. The defect formation energy is minimum and the solubility is highest for the B-N co-doping system. The configurations of adjacent impurity atoms are easier to form in B-N co-doping diamond, i.e. NBN and BNN. The NBN impurity can introduce a shallow donor level (0.55 eV) in diamond, while the enhanced contribution of N atoms to the impurity state leads to the creation of deep donor level in diamond for the BNN impurity. The current paper clearly demonstrates that the NBN complex is a possible candidate for the preparation of n-type diamond from the theoretical aspect, providing a solid theoretical basis for experimental studies on the B and N co-doping scheme.

Tailoring the electric, dielectric and optical properties of template-free hydrothermally synthesized CuO nanostructures via Co doping

Facile template-free hydrothermal method was utilized for preparing CuO nanostructures (NSs) doped with Co element (Cu1-xCoxO (x = 0.0, 0.02, 0.04, 0.06 and 0.08)). A single-phase monoclinic crystal with changing in morphology from rod-to sphere-like nanoparticles was observed. The temperature dependency of DC electrical conductivity revealed that the shallow and deep donor levels are responsible for the DC conduction in low and high temperature ranges, respectively. The Ac electrical conductivity, dielectric constant and dielectric loss were also measured as functions in frequency and temperature. The frequency dependence of the AC conductivity was well represented by the Jonscher's universal power law. The AC conduction was governed by the Correlated Barrier Hopping model where the inter-well and intra-well hopping mechanisms contribute to the electrical conduction in the low and high frequency ranges, respectively. The activation energies and the barrier height decreased while the dielectric constant and dielectric loss increased with increasing the Co content. The relaxation and deformational polarizations predominate and the overall behavior of dielectric constant fits well with the Koops' model. The Cole-Cole plots indicated a decrease in the sample resistance with increasing temperatures and Co concentrations. UV–vis absorption spectra exhibited two peaks at wavelengths 252 and 323 nm. The optical energy gap was calculated using Tauc's equation and decrease from 2.24 to 2.1 eV with increasing the Co concentrations. The effect of Co-doping on CuO was explored for oxygen evolution reaction (OER) and found a decrease in the overvoltage (μ) about 50 mV at 0.08 ratios, which declares that the doping of Co element enhances the electrical conductivity and feasibility for further electrocatalytic improvement.

Green Synthesis of Metal-Doped ZnO Nanoparticles Using Bauhinia racemosa Lam. Extract and Evaluation of Their Photocatalysis and Biomedical Applications.

A fascinating problem in the fields of nanoscience and nanobiotechnology has recently emerged, and to tackle this, the production of metal oxide nanoparticles using plant extracts offers numerous benefits over traditional physicochemical methods. In the present investigation, ZnO nanoparticles were fabricated from Bauhinia racemosa Lam. (BR) leaves extract with various transition metal (TM) dopants (Ni, Mn, and Co). Plant leaves extract containing metal nitrate solutions were utilized as a precursor to synthesize the pristine and TM-doped ZnO nanoparticles. Structural, functional, optical, and surface properties of the fabricated samples were studied by using physicochemical and photoelectrochemical measurements. The organic pollutants tetracycline (TC), ampicillin (AMP), and amoxicillin (AMX) were used in the photocatalytic degradation assessment of the fabricated samples. Through X-ray diffraction (XRD) and transmission electron microscopy (TEM) investigation, the fabricated nanoparticles wurtzite crystal structure was verified. Moreover, Fourier transform infrared (FT-IR) analysis verified the existence of functional groups in the fabricated nanoparticles. The migration of electrons from the deep donor level and zinc interstitial to the Zn-defect and O-defect is related to the emission peaks seen at 468, 480, 534, and 450 nm in photoluminescence (PL) spectra. Co-ZnO nanoparticles demonstrated potent and excellent photocatalytic degradation performance for TC (91.09%), AMP (87.97%), and AMX (92.42%) antibiotics within 210, 180, and 150 min of visible light irradiation. Co-ZnO nanoparticles also demonstrated strong antimicrobial performance against Escherichia coli, Staphylococcus aureus, Klebsiella pneumoniae, Aspergillus flavus, Aspergillus niger, and Bacillus subtilis. Further investigation of in vitro cytotoxic potential against the A549 cell line (IC50 = 24 ± 0.5 μg/mL) utilizing MTT assay and the free radical scavenging performance of Co-ZnO nanoparticles estimated by DPPH assay utilizing l-ascorbic acid as a reference was also performed. Anti-inflammatory potential is also reviewed by comparing it with the standard drug Diclofenac, and the maximum activity was obtained for Ni-ZnO nanoparticles (IC50 = 72.4 μg/mL).

Electron-Phonon Coupling-Mediated Ultralong Carrier Lifetime in an All-Inorganic Two-Dimensional Cs2PbI2Cl2 Perovskite: Explanation for the High Antisite Defect Tolerance.

Two-dimensional (2D) halide perovskite are appealing candidates for applications in optoelectronics and photovoltaics, but their energy conversion efficiency is severely limited by nonradiative electron-hole recombination. In most investigations, point defects with deep defect levels and deep charge-state transition levels in the band gap are treated as the carrier recombination centers. For the all-inorganic 2D Css 2PbI2Cl2, the IPb antisite defect is the most likely to form and cause nonradiative electron-hole recombination. By using density functional theory and ab initio nonradiative molecular dynamics calculations, we found that the IPb defect can introduce the deep acceptor and donor levels into the band gap. Because electron-phonon coupling gives rise to weak nonadiabatic coupling and rapid loss of electronic coherence, those levels lead to a reduction of the carrier loss and the prolongation of the excited-state carrier lifetime, thereby enhancing the photoelectric and defect tolerance properties of the Cs2PbI2Cl2 material. These results could deepen the understanding of the chemistry of defects and carrier dynamics in perovskite materials.

Comprehensive electrical characterization and theoretical analysis of Mn and As doped β-FeSi2 through DFT: A promise to rectification and photovoltaic applications

The effects of Mn and As doping in β-FeSi2 have been studied by theoretical simulations and electrical characterizations by analyzing Hall parameters within the temperature range of 20–300 K using mobility and the dual band model. The Hall resistivity ρ of doped samples increases linearly from a negative to a positive magnetic field (B), demonstrating the normal Hall effect at room temperature. High temperature Hall concentration increases significantly with the gradual increase in both Mn and As doping due to more and more ionization of the deep donor level. High temperature activation energies of Mn doped β-FeSi2 are considerably greater than that of low temperature energies, which demonstrates clear evidence of the dual band model. From density functional theory calculations, the origin of the dual band model has been validated from the electronic structure of β-FeSi2. Both density of states and charge transfer to the system upon doping have been investigated through the density functional theory, which demonstrates the Mn and As doped systems to be p-type and n-type, respectively. Both Mn and As doped β-FeSi2 exhibit p-type and n-type conductivities for spin down and spin up channels, respectively, in the presence of an external magnetic field, which will encourage its applications in novel spintronic devices. In addition, a β-FeSi2 based homo-junction diode fabricated from the Mn and As doped β-FeSi2 exhibits a cut-in voltage of 0.82 V, a reverse breakdown voltage of −10 V, and an ideality factor of 3.87. Thus, doped β-FeSi2 will be very much useful for fabricating an efficient and cost-effective solar cell if fabricated physically.

Optical, structural, electrical and photocatalytic properties of aluminum doped zinc oxide nanostructures

The Al-doped ZnO (Zn1-xAlxO, x = 0.00, 0.02, 0.04, 0.06, and 0.08) nanostructures were synthesized by the chemical vapor deposition technique. Analysis by X-ray diffraction reveals that both undoped and Al-doped ZnO nanostructures are crystallized in a single-phase wurtzite structure with a preferred orientation along the (101) plane. The addition of Al was studied to see how it influenced bond length, crystallite size, unit cell volume, lattice strain, and dislocation density. Field-emission scanning electron microscope imaging showed a significant variation in the morphology with increasing the Al doping level. Absorption spectra in the UV–Visible range revealed that introducing Al3+ ions into the ZnO lattice causes a blue shift in the optical band gap, which was explained according to Burstein-Moss effect and variation of the electronic structure. The direct electrical conductivity measurement showed a transformation between two conduction mechanisms upon variation of the temperature. Transition of the charge carriers from shallow and deep donor levels dominated in the low and high temperature ranges, respectively. The photodegradation rate constants and degradation efficiency were determined as well as the photocatalytic mechanism was described. Upon reaching the x = 0.08 Al doping level, the photocatalytic efficiency of the examined samples increased by 1.7-fold. The obtained results demonstrate that Al doping can tune the electrical, optical, and photocatalytic properties of ZnO nanostructures that make them applicable for many optoelectronic applications.

Determination of CN deep donor level in p-GaN with heavy Mg doping via a carrier statistics approach

An equilibrium carrier statistics approach with a partial ionization model is proposed to determine the energy level of CN deep donors in p-type GaN with heavy Mg doping. Unlike usual compensating centers that are assumed to be fully ionized under equilibrium, partial ionization of the CN donor was taken into consideration. The energy level of the CN donor is determined to be EV + (0.20 ± 0.01) eV at elevated temperatures (∼350 K) using such a partial ionization model. The donor level for an isolated C center at a low temperature limit is further calculated considering the doping and temperature effects, which is EV + (0.32 ± 0.01) eV. Furthermore, the ionization ratio of CN is found to be dependent on the C concentration and can then be estimated to be in the range of 0.3–0.8. Such a partial ionization characteristic of CN may capture/emit free carriers during device operation and should be taken into account when analyzing device reliability.

Enhanced thermoelectric performance of InSb through deep level impurity donor state induced by La doping

As one member of III-V semiconductors that have a variety of applications, InSb also shows great potential in thermoelectrics owing to its high mobility. In this work, the thermoelectric performance of n-type polycrystalline InSb is improved by La doping, which induces deep level impurity donor state and massive defects, synergistically optimizing both electrical and thermal transport properties. The peak power factor of La-doped InSb is enhanced from 42 to 58 μW cm−1 K−2 at 773 K due to the enlarged carrier concentration provided by the deep level donor state. Meanwhile, lattice thermal conductivity decreases from 3.2 to 1.7 W m−1 K−1 at 773 K due to In precipitates, point defects and local atomic disorder. Consequently, the peak zT of La-doped InSb is promoted to 0.85 at 773 K, which is among the best value in III-V compounds.

Electronic transport properties of Ti-supersaturated Si processed by rapid thermal annealing or pulsed-laser melting

In the scope of supersaturated semiconductors for infrared detectors, we implanted Si samples with Ti at high doses and processed them by rapid thermal annealing (RTA) to recover the crystal quality. Also, for comparative purposes, some samples were processed by pulsed-laser melting. We measured the electronic transport properties at variable temperatures and analyzed the results. The results indicate that, for RTA samples, surface layers with a high Ti concentration have negligible conductivity due to defects. In contrast, the implantation tail region has measurable conductivity due to very high electron mobility. This region shows the activation of a very shallow donor and a deep donor level. While deep levels have been previously reported for Ti in Si, such a shallow level has never been measured, and we suggest that it originates from Ti-Si complexes. Finally, a decoupling effect between the implanted layer and the substrate seems to be present, and a bilayer model is applied to fit the measured properties. The fitted parameters follow the Meyer–Neldel rule. The role of the implantation tails in Si supersaturated with Ti is revealed in this work.

Intrinsic defect-induced magnetism and enhanced photocatalytic activity in Zn1−xZrxO (0.0 ≤ x ≤ 0.07) nanoparticles for spintronic device and photocatalytic application

In this study, ZnO nanoparticles were synthesized by sol-gel auto combustion technique with and without Zr4+ doping. The synthesized nanoparticles were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray analysis (EDAX), selected area diffraction pattern (SAED), transmission electron microscopy (TEM), photoluminescence spectroscopy (PL), fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance spectroscopy (EPR). A rietveld refinement analysis was performed using fullprof software on the XRD patterns of ZnO and Zr4+ doped ZnO nanoparticles, analysis showed a hexagonal wurtzite structure with an average crystallite size between 19 and 15 nm. SEM were employed to examine the surface morphology. TEM used to determine the particle size and size distribution histogram. SAED pattern confirmed the single-crystalline wurtzite structure. The compositional stoichiometry was verified by energy dispersive spectroscopy (EDAX). The PL spectrum reveals UV emission at the near band edge, as well as defect-related blue and green emission. In the PL spectrum, the green emission of Zr doped ZnO nanoparticles correlates strongly with their magnetic properties.An oxygen vacancy defect was confirmed by EPR studies for Zr doped ZnO nanoparticles. Sample (x = 0.03) exhibited very high coercivity value due to higher oxygen vacancies (Vo). X-ray photoelectron spectroscopy showed the oxidation state of Zn and Zr4+ atoms exist as Zn2+ and Zr4+ in the ZnO structure respectively. A vibrating sample magnetometer (VSM) was used to quantify the magnetic properties. Field-dependent magnetization measurements show diamagnetic behavior for pristine and Zr (x = 0.01 mol) doped ZnO. However, other doped samples (x = 0.03, 0.05, and 0.07 mol) exhibited ferromagnetic behavior at room temperature due to intrinsic defects (Zni and Vo). A UV–visible absorption spectrum was used to determine the energy band gap. Compared with pristine ZnO nanoparticles, doped samples exhibit a redshift in absorption edge. In addition, the photocatalytic activity of synthesized samples was determined by degrading the dye methylene blue (M.B.) in the presence of sunlight. An extensive evaluation of the effect of Zr concentrations on photocatalytic degradation was conducted. Zr4+ doped ZnO nanoparticles exhibit emission peaks detected at 424, 446, and 573 nm. These emission peaks result from electron movement from the deep donor level, zinc interstitial (Zni), and oxygen vacancy(Vo), which ultimately leads to higher photocatalytic efficiency.

Assessing defect-assisted emissions in indirect bandgap BaSi2 by photoluminescence

Undoped BaSi2 epitaxial layer on Si(111) substrate grown at a Ba-to-Si deposition rate ratio (RBa/RSi) of 0.7,1.2 and 3.7 were studied by power dependent photoluminescence (PL). At 10 K, sample 0.7 and 1.2 showed weak PL spectra while sample 3.7 showed two distinct peaks at high energy side and a broad emission at low energy side. The PL spectra were then deconvoluted using two to four Gaussian curves. The results displayed a non-linear power law suggesting a transition between two limiting power law exponents. Then, power law exponents for cases with shallow and deep levels were calculated and compared to the experiment. It was found that for low RBa/RSi, transition between shallow donor and shallow acceptor dominated the luminescence (PL peak energy of 1.12 eV). Deep donor and deep acceptor started to appear with increasing RBa/RSi and lead to additional transitions with energies of 1.05, 0.976 and 0.878 eV. Analysis carried out suggested that the donor levels may correspond to Si vacancies while deep and shallow acceptors may correspond to Ba antisites and Si interstitials, respectively. We propose that BaSi2 should be grown at low RBa/RSi to avoid the formation of deep donor level and high density of Ba antisites.

Defect engineered blue photoluminescence in ZnO:Al/TiO2 heterostructures

Tailoring the blue photoluminescence (PL) in Al-doped ZnO (AZO)/TiO2 heterostructures is demonstrated by a controlled induction of shallow defect centers by 50 keV Ar+-ions. This is established by a combination of temperature dependent PL and electron paramagnetic resonance spectroscopy. The dominant blue-violet PL in an as-grown sample comprises a near band-edge emission, along with a peak associated with a radiative recombination of the electrons in shallow donor levels (Zn interstitials) and the holes from the valence band. However, the evolution of an additional yellow-green PL band at a fluence of 1 × 1015 ions/cm2 is governed by deep donor levels, particularly ionized oxygen vacancies. Irradiation at 1 × 1016 ions/cm2 further leads to the formation of Zn vacancies (shallow acceptors) owing to the development of an O-rich surface. The structural modifications of these samples have been investigated by field-emission scanning electron microscopy , transmission electron microscopy, and Rutherford backscattering. While small micro-cracks are found at a fluence of 2 × 1016 ions/cm2, the formation of graded layers is obtained at the highest fluence of 5 × 1016 ions/cm2 owing to ballistic intermixing and diffusion of the constituents. Detailed investigation suggests that a significant amount of Ti atoms is diffused in AZO by a complete deterioration of the AZO/TiO2 matrix at the highest fluence.

Magnetic Order, Electrical Doping, and Charge-State Coupling at Amphoteric Defect Sites in Mn-Doped 2D Semiconductors.

Two-dimensional (2D) dilute magnetic semiconductors (DMSs) are attractive material platforms for applications in multifunctional nanospintronics due to the prospect of embedding controllable magnetic order within nanoscale semiconductors. Identifying candidate host material and dopant systems requires consideration of doping formation energies, magnetic ordering, and the tendency for dopants to form clustered domains. In this work, we consider the defect thermodynamics and the dilute magnetic properties across charge states of 2D-MoS2 and 2D-WS2 with Mn magnetic dopants as candidate systems for 2D-DMSs. Using hybrid density functional calculations, we study the magnetic and electronic properties of these systems across configurations with thermodynamically favorable defects: 2D-MoS2 doped with Mn atoms at sulfur site (MnS), at two Mo sites (2MnMo), on top of a Mo atom (Mn-top), and at a Mo site (MnMo). While the majority of the Mn-defect complexes provide trap states, MnMo and MnW are amphoteric, although previously predicted to be donor defects. The impact of cluster formation of these amphoteric defects on magnetic ordering is also considered; both MnMo-MnMo (2Mn2Mo) and MnW-MnW (2Mn2W) clusters are found to be stable in ferromagnetic (FM) ordering. Interestingly, we observed the defect charge state dependent magnetic behavior of 2Mn2Mo and 2Mn2W clusters in 2D-TMDs. We investigate that the FM coupling of 2Mn2Mo and 2Mn2W clusters is stable in only a neutral charge state; however, the antiferromagnetic (AFM) coupling is stable in the +1 charge state. 2Mn2Mo clusters provide shallow donor levels in AFM coupling and deep donor levels in FM coupling. 2Mn2W clusters lead to trap states in the FM and AFM coupling. We demonstrate the AFM to FM phase transition at a critical electron density nce = 3.5 × 1013 cm-2 in 2D-MoS2 and 2D-WS2. At a 1.85% concentration of Mn, we calculate the Curie temperature of 580 K in the mean-field approximation.

A DFT study on the electronic structure, magnetic and optical properties of Er doped ZnO: Effect of Er concentration and native defects

We report on first-principles study of the effect of Er concentration and intrinsic defects (VO and VZn) on the electronic structure and optical properties of Er-doped ZnO using the GGA + U method. The lattice constants and band gap of ZnO calculated in this work are in agreement with experimental values. The results showed that the band gap of Er-doped ZnO decreases with increasing Er concentration, while it increases with the presence of O or Zn vacancies. Furthermore, the existence of VO causes the formation of a deep donor level in the band gap. Er–ZnO + VZn is a degenerate p-type semiconductor, and shallow acceptor states are created near the Fermi level. The magnetic moment of doped ZnO increases and Er 4f electrons are responsible for the induced magnetic moments. The absorption coefficient enhances in the visible range in Er doped ZnO. In the Er–ZnO + VO model, both absorption and reflection are relatively enhanced in the visible range, leading to a decrease in light transmittance. Hence, the magneto-optoelectronic properties of ZnO could be improved by an optimal concentration of Er as well as with the presence of oxygen vacancies.

Fabrication of inversion p-channel MOSFET with a nitrogen-doped diamond body

A normally-off inversion p-channel metal-oxide-semiconductor field-effect transistor (MOSFET) with a nitrogen (N)-doped diamond body deposited using microwave plasma-enhanced chemical vapor deposition (MPECVD) was fabricated. The MOSFET exhibited a drain current density of −1.7 mA/mm. Thus far, this value is similar to the device performance of the inversion p-channel MOSFET fabricated using a phosphorus (P)-doped n-type diamond body. The N2 used for N-doping is safer than the PH3 used for P-doping; moreover, the doping concentration is highly controllable. Because the MOSFET, which is a classical electronic device, is driven by a gate voltage, smooth functioning was possible even at a deep donor level. The observed characteristics of the classic MOSFET operating via an N-doped body are crucial for the development of diamond power devices. In this paper, we discuss the significance of the N-doped diamond body and electrical characteristics of the inversion p-channel MOSFET fabricated using an N-doped diamond body.

Optical and structural characterization of high crystalline β-Ga2O3 films prepared using an RF magnetron sputtering

β-Ga2O3 films have been prepared on sapphire (0001) substrate using an RF magnetron sputtering. The highly oriented β-Ga2O3 films with a high crystallinity could be obtained at Ts above 700 °C. The sputtered film in pure Ar showed a low optical band-gap and a strong optical absorption in UV and visible region, possibly due to non-stoichiometry, oxygen-deficiency. Raman modes of β-Ga2O3 started to evolve at Ts of 400 °C and then, were clearly defined and dominant at Ts above 600 °C in a good consistence with XRD result. In the PL spectra at Ts above 600 °C, UV emission peaked at 3.75 eV and red-emission composed of broad band and sharp peaks were predominant. These emissions are the first report in PL spectra of β-Ga2O3 and have been tentatively assigned to high energy excitons caused by electrons trapped with holes at deeper acceptor level, and optical transition between deep donor level and delocalized/clustered acceptor levels, respectively.

Green synthesis of Cu-doped ZnO nanoparticles and its application for the photocatalytic degradation of hazardous organic pollutants

In recent times, the synthesis of metal nanoparticles (NPs) using plant extracts has recently emerged as an intriguing issue in the field of nanoscience and nanobiotechnology, with numerous advantages over conventional physicochemical approaches. In the current study, ZnO NPs were synthesized from Synadium grantii leaf extricate with varying Cu-dopant concentrations. In order to the synthesis of the pure and Cu-doped ZnO NPs, zinc nitrate hexahydrate and copper nitrate trihydrate were used as a precursor in leaf extracts of the plant. XRD, TEM, FTIR, XPS, and PL measurements were carried out to examine the physical and optical properties of the synthesized samples. The photocatalytic studies of the prepared samples were studied using Methylene blue (MB), Indigo Carmine (IC), and Rhodamine B (RhB) organic pollutants. The wurtzite crystal structure of synthesized samples was confirmed by XRD and TEM analysis. Further, the presence of functional groups in the prepared samples was confirmed by FTIR analysis. XPS analysis confirmed that the binding energies of a host material and dopant ions. The emission peaks identified at 424, 446 and 573 nm are associated with the electron movement from the deep donor level, zinc interstitial to the zinc vacancy and oxygen vacancy. 3% and 5% Cu-doped samples exhibited superior photocatalytic activity for MB, IC, and RhB dyes. The green synthesized ZnO NPs showed enriched photocatalytic performance, signifying that bio-synthesis can be an outstanding approach to develop versatile and environmental products.

More Se Vacancies in Sb2Se3 under Se‐Rich Conditions: An Abnormal Behavior Induced by Defect‐Correlation in Compensated Compound Semiconductors

It was believed that the Se-rich synthesis condition can suppress the formation of deep-level donor defect VSe (selenium vacancy) in Sb2 Se3 and is thus critical for fabricating high-efficiency Sb2 Se3 solar cells. However, here it is shown that by first-principles calculations the density of VSe increases unexpectedly to 1016 cm-3 when the Se chemical potential increases, so Se-rich condition promotes rather than suppresses the formation of VSe . Therefore, high density of VSe is thermodynamically inevitable, no matter under Se-poor or Se-rich conditions. This abnormal behavior can be explained by a physical concept "defect-correlation", i.e., when donor and acceptor defects compensate each other, all defects become correlated with each other due to the formation energy dependence on Fermi level which is determined by densities of all ionized defects. In quasi-1D Sb2 Se3 , there are many defects and the complicated defect-correlation can give rise to abnormal behaviors, e.g., lowering Fermi level and thus decreasing the formation energy of ionized donor VSe 2+ in Se-rich Sb2 Se3 . Such behavior exists also in Sb2 S3 . It explains the recent experiments that the extremely Se-rich condition causes the efficiency drop of Sb2 Se3 solar cells, and demonstrates that the common chemical intuition and defect engineering strategies may be invalid in compensated semiconductors.

Distinguishing persistent effects in an undoped GaAs/AlGaAs quantum well by top-gate-dependent illumination

Persistent photoconductivity of GaAs/AlGaAs heterostructures has hampered the measurement of charge- and spin-related quantum effects in gate-defined quantum devices and integrated charge sensors due to Si-dopant-related deep donor levels (DX centers). In this study, this effect is overcome by using an undoped GaAs/AlGaAs heterostructure for photonic purposes. We also measure the electron transport before and after LED illumination at low temperatures. In addition to a regular rapid saturation showing the increased carrier density, a slow accumulation of illumination effects appeared when different top-gate voltages were applied during illumination, which indicated the redistribution of charge at the oxide–GaAs interface. This study provides interesting insights into the development of optically stable devices for efficient semiconductor quantum interfaces.

A comparable study of structural models and donor levels for S doping and B–S co-doping in diamond

In this study, we predict two kinds of stable structural models of B–S co-doped diamond through molecular dynamic simulations and geometrical optimization by density functional theory. The bond lengths and electron distribution near the dopants are similar with those of substitutional S in diamond with C3v symmetry. The B–S co-doped diamond shows the deep donor level, which is mainly contributed by the dopants and adjacent C atoms. Furthermore, the structures show the localized electron distribution near the dopants from the lone-pair electron around S atom.