The electronic levels of vanadium in semi-insulating 4H- and 6H-SiC have been reinvestigated using temperature dependent Hall effect and resistivity measurements at temperatures up to 1000 K in conjunction with electron paramagnetic resonance (EPR) and optical absorption measurements... (Read more)

We study the effect of confinement on the spin polarization of holes bound to Mn acceptors in paramagnetic GaAs:Mn/AlAs multiple quantum wells. It is demonstrated that the polarization of these bound holes is governed by the properties of the host material rather than by quantum confinement. The... (Read more)

Silicon carbide nanotubes have a great potential for biological applications. It is of interest to explore the electronic properties of these nanotubes, and how those are modified in the presence of impurities. Hydrogen is a common impurity that can appear during the growth of silicon carbide... (Read more)

We have investigated the superconductivity discovered in boron-doped diamonds by means of ¹¹B-NMR on heteroepitaxially grown (111) and (100) films. ¹¹B-NMR spectra for all of the films are identified to arise from the substitutional B(1) site as single occupation and lower... (Read more)

The asymmetry doping problem has severely hindered the potential applications of many wideband gap (WBG) materials. Here, we propose a possible approach to overcome this long-standing doping asymmetry problem for WBG semiconductors. Our approach is based on the reduction of the ionization energies... (Read more)

The Stark splitting of a single fourfold degenerate impurity located within the built-in potential of a metal-semiconductor contact is investigated using low temperature transport measurements. A model is developed and used to analyze transport as a function of temperature, bias voltage, and... (Read more)

Existing defect models for In₂O₃ and ZnO are inconclusive about the origin of conductivity, nonstoichiometry, and coloration. We apply systematic corrections to first-principles calculated formation energies ΔH, and validate our theoretical defect model against... (Read more)

Boron strongly modifies electronic and diffusion properties of graphite. We report the first ab initio study of boron interaction with the point defects in graphite, which includes structures, thermodynamics, and diffusion. A number of possible diffusion mechanisms of boron in graphite are... (Read more)

The spin relaxation process of acceptor-bound excitons in wurtzite GaN is observed by spin-dependent pump and probe reflectance measurement with subpicosecond time resolution. The time evolutions measured at 15–50 K have a single exponential component corresponding to the electron spin... (Read more)

Recombination centers in thin asymmetrical p-n junctions were analyzed in the context of capacitance transient experiments. The combined effect of the thin low-doped region of the junction and the nonzero value of the occupation factor of the recombination center in the depletion layer... (Read more)

The authors report the observation of both acceptor- and donorlike defects in ZnO by deep level transient spectroscopy. The observation is facilitated by using a p-n junction allowing the injection of holes and electrons. The junction is realized by implanting a n-conducting ZnO... (Read more)

We investigate photoluminescence from reproducible Li-doped p-type ZnO thin films prepared by dc reactive magnetron sputtering. The Li_Zn acceptor state, with an energy level located at 150 meV above the valence band maximum, is identified from free-to-neutral-acceptor transitions.... (Read more)

The current-voltage characteristics with acceptor segregation at grain boundaries have been investigated in H₂-sintered SrTiO₃. Al-added SrTiO₃ was sintered in H₂ and then annealed in air for selective oxidation of grain boundaries. The samples showed... (Read more)

Phosphorus-doped ZnO films were grown by molecular-beam epitaxy with a GaP effusion cell as dopant source. Three growth regions were identified to obtain ZnO films with different conduction types. In the oxygen-extremely-rich region, phosphorus-doped ZnO films show n-type conduction with... (Read more)

This paper addresses some of the fundamental issues and critical advantages in reducing the grain size/feature size to the nanoscale regime. We find that as the grain size or feature size is reduced, there is a critical size below which the defect content can be reduced virtually to zero. This... (Read more)

The discovery of ferromagnetism in Mn-doped GaAs1 has ignited interest in the development of semiconductor technologies based on electron spin and has led to several proof-of-concept spintronic devices2, 3, 4. A major hurdle for realistic applications of Ga_1-XMn_XAs, or other dilute magnetic semiconductors, remains that their ferromagnetic transition temperature is below room temperature. Enhancing ferromagnetism in semiconductors requires us to understand the mechanisms for interaction between magnetic dopants, such as Mn, and identify the circumstances in which ferromagnetic interactions are maximized5. Here we describe an atom-by-atom substitution technique using a scanning tunnelling microscope (STM) and apply it to perform a controlled study at the atomic scale of the interactions between isolated Mn acceptors, which are mediated by holes in GaAs. High-resolution STM measurements are used to visualize the GaAs electronic states that participate in the Mn–Mn interaction and to quantify the interaction strengths as a function of relative position and orientation. Our experimental findings, which can be explained using tight-binding model calculations, reveal a strong dependence of ferromagnetic interaction on crystallographic orientation. This anisotropic interaction can potentially be exploited by growing oriented Ga_1-XMn_XAs structures to enhance the ferromagnetic transition temperature beyond that achieved in randomly doped samples. (Read more)

The density (N_A) and energy level (E_A) of an acceptor in a p-type wide-band-gap semiconductor (e.g., SiC, GaN, and diamond) are determined by a least-squares fit of the charge neutrality equation to the temperature dependence of the hole... (Read more)

We applied x-ray absorption spectroscopy and x-ray magnetic circular dichroism (XMCD) at the Mn 2p-3d resonances to study the Mn 3d electronic configuration and the coupling of Mn 3d magnetic moments in various Ga_1−xMn_xAs films.... (Read more)

Experimental studies of Zn_1−xCo_xO as thin films or nanocrystals have found ferromagnetism and Curie temperatures above room temperature and that p- or n-type doping of Zn_1−xCo_xO can change its magnetic... (Read more)

p-type doping is a great challenge for the full utilization of ZnO as short-wavelength optoelectronic material. Due to a large electronegative characteristic of oxygen, the ionization energy of acceptors in ZnO is usually too high. By analyzing the defect wave-function character, we propose... (Read more)

B diffuses in crystalline Si by reacting with a Si self-interstitial (I) with a frequency g and so forming a fast migrating BI complex that can migrate for an average length λ. We experimentally demonstrate that both g and λ strongly depend on the free hole... (Read more)

The role of Pr doping on double Schottky barrier formations at ZnO single grain boundaries was investigated by the combination of current-voltage measurements, atomic-resolution Z-contrast scanning transmission electron microscopy, and first-principles calculations. Although Pr segregated to... (Read more)

The microscopic process involved with thermal activation of the Mg acceptors in GaN epitaxial films is investigated using electron paramagnetic resonance (EPR) spectroscopy. Samples were heat treated in dry N₂ for 30 min at temperatures between 200 and 1000 °C. Below 850 °C, the... (Read more)

Band gap states of platinum and iridium in the hexagonal polytype 4H of silicon carbide are investigated by means of deep level transient spectroscopy (DLTS) in n- as well as p-type epitaxial layers. To establish a definite chemical assignment of band gap states to Pt and Ir the... (Read more)

The interstitial and vacancy mediated boron diffusion in silicon carbide is investigated with an ab initio method. The boron interstitials in p-type and n-type materials are found to be far more mobile than the boron-vacancy complexes. A kick-out mechanism and an interstitialcy... (Read more)

The diffusion of interstitial atomic hydrogen in 4H-SiC was investigated theoretically, using the local density approximation of density functional theory. We have found that the diffusion barrier in the perfect crystal is 0.6 eV. Comparing this value with the calculated zero point vibration... (Read more)

In this paper we analyze, by means of first-principles electronic structure calculations, the structural, energetic, and diffusive properties of B impurities in SiC as well as of vacancies. We focus our study on (i) determining the equilibrium structures of the impurity in the lattice by means of... (Read more)

Electron paramagnetic resonance (EPR) has been used to investigate molecular nitrogen and isolated nitrogen acceptors in single crystals of ZnO. These samples were grown by the seeded chemical vapor transport method with N₂ added to the gas stream. A five-line EPR spectrum is observed at... (Read more)

The oxidation states of Mn in epitaxial GaN films grown by plasma induced molecular beam epitaxy were investigated by electron spin resonance (ESR), elastic recoil detection, superconducting quantum interference device magnetization, and photothermal deflection spectroscopy measurements. Comparison... (Read more)

A defect associated with Li in ZnO is reported. This is an optical system which absorbs strongly in the red part of the spectrum: a doublet, the zero phonon lines are at 1.884 and 1.879 eV, respectively. The chemical nature of the centre is identified through isotope substitution. This is the first... (Read more)

Nitrogen acceptors are formed when undoped single crystals of zinc oxide (ZnO) grown by the chemical-vapor transport method are annealed in air or nitrogen atmosphere at temperatures between 600 and 900 °C. After an anneal, an induced near-edge absorption band causes the crystals to appear... (Read more)

We will highlight our recent work on the properties of residual defects and dopants in GaN heteroepitaxial layers and on the nature of recombination from InGaN single quantum well (SQW) light emitting diodes (LEDs) through magnetic resonance techniques. Electron paramagnetic resonance (EPR) and... (Read more)

Previous calculations on n-type doping of diamond by P and S predicted that S has a shallower level and a higher solubility than P. Our first-principles calculations show that the opposite is true: Phosphorus impurity in diamond gives rise to a shallower donor level, and has a higher bulk solid... (Read more)

Electron paramagnetic resonance (EPR) and optically detected magnetic resonance (ODMR) experiments have been performed on a set of GaN epitaxial layers doped with Mg from 2.5?10¹⁸ to 5.0?10¹⁹ cm^-3. The samples were also characterized by secondary-ion-mass... (Read more)

Photosensitive electron paramagnetic resonance (EPR) investigations of unintentionally doped, semi-insulating (s.i.) 4H?SiC have been made at 37 GHz and 77 K including photoexcitation and photoquenching experiments. In the dark the EPR spectrum consists of a low intensity line due to boron on the... (Read more)

We have used EPR and ODMR to study state-of-the-art bulk ZnO single crystals. Most of the samples are n-type; however, under certain conditions (e-irradiated or annealed), we observe a center due to residual nitrogen (g||=1.9953, g=1.9633 and Aiso=1.225 mT, Aaniso=0.864 mT). The N center is a... (Read more)

Semi-insulating (SI) silicon carbide is important for applications in high-power, high-frequency electronics, such as SiC MESFETs and GaN FETs. In this work, we discuss the use of low-temperature electron paramagnetic resonance (EPR), room- and low-temperature FTIR and photoluminescence as potential... (Read more)

Magnetic resonance experiments, including optically detected magnetic resonance (ODMR) and electron paramagnetic resonance (EPR), have been performed on Si-doped homoepitaxial GaN layers grown by MOCVD and on high quality, free-standing (200 μm-thick) GaN grown by HVPE. This allowed us to... (Read more)

Nominally undoped and Mg-doped wurtzite GaN grown with MOVPE on sapphire substrates were investigated with photoluminescence-detected electron paramagnetic resonance (PL-EPR). For enhanced resolution a microwave frequency of 72 GHz (V-band) was used. PL-EPR was measured via the yellow luminescence... (Read more)

A high-frequency (95 GHz) and conventional-frequency (9.3 GHz) pulsed electron paramagnetic resonance and electron-nuclear double resonance (ENDOR) study is reported on the deep boron acceptor in 6H-SiC. The results support a model in which the deep boron acceptor consists of a boron on a silicon... (Read more)

Investigations of nitrogen donors in 6H-, 4H- and 3C-SiC using conventional electron paramagnetic resonance (EPR), electron nuclear double resonance (ENDOR) and optical detection of EPR and ENDOR as well as optical absorption and emission spectroscopy are reviewed and critically discussed. An... (Read more)

The B-H complex in Si can be aligned by stress and reorients with an activation energy of roughly 0.2 eV. We combine new measurements of the reorientation kinetics of the B-H complex made by the stress-induced dichroism technique with previous internal friction results to show that the reorientation... (Read more)

Optically detected magnetic resonance has been observed from GaN. Two magnetic resonances have been detected on the 2.2 eV-deep photoluminescence band. The first resonance is sharp [full width at half-maximum (FWHM) ~2.2 mT] with g=1.9515±0.0002 and... (Read more)

The interactions between interstitial H and substitutional B, C, and Si in crystalline silicon and germanium are studied in molecular clusters at the ab initio Hartree-Fock level with large basis sets. The energetics, electronic structures, and relative stabilities of these pairs are determined. Our... (Read more)

Tungsten deep levels are investigated to clarify energies, which are inconsistent among current research. Hole traps located at 0.41 eV above the top of the valence band are determined to be due to tungsten impurities. The concentration of hole traps is almost one-third of that of the tungsten... (Read more)

The elastic energy loss between 60 and 300 K was measured in SiB_xH_y at frequencies between 2.4 and 32 kHz. A single-time relaxation process appears in the neighborhood of 130 K, which is due to the stress-induced jumps of H around B, with a relaxation time... (Read more)

The behavior of hydrogen in crystalline silicon is examined with state-of-the-art theoretical techniques, based on the pseudopotential-density-functional method in a supercell geometry. Stable sites, migration paths, and barriers for different charge states are explored and displayed in total-energy... (Read more)

The motion of hydrogen in the B-H complex in silicon has been studied. An applied stress is used to produce a preferential alignment of the B-H complex at temperatures sufficiently high for the H to move within the complex (above ∼60 K). This alignment of the complexes is detected by comparing the... (Read more)

B-doped Si wafers were subjected to atomic-deuterium (D) plasmas to simulate the reactions of atomic hydrogen with substitutional B acceptor levels. Secondary ion mass spectrometry was used to profile the in- and out-diffusion of D, and spreading resistance was used to measure the distribution of... (Read more)

Experimental results are presented which identify the following chemical reaction as being responsible for compensation of shallow-acceptor impurities when single-crystal silicon is exposed to monatomic hydrogen: A^-+h⁺+H⁰↔(AH)⁰, where A^-... (Read more)

Application of optically detected ESR to the yellow photoluminescence of Li doped ZnO gives ESR spectra for shallow donor - lithium acceptor pairs, showing that at least a fraction of the yellow emission is donor-acceptor (D-A) luminescence. The distribution of separations rDA gives a spectrum of... (Read more)

The solubilities of substitutional and interstitial copper (Cu^s and Cuⁱ) have been measured in intrinsic and extrinsic n- and p-type Ge, Si, and GaAs, using Cu⁶⁴. These measurements show that Cu^s is a triple acceptor in... (Read more)

A theory of paramagnetic resonance on acceptor centres in deformed and non-deformed Ge and Si type crystals is developed. The splitting of the ground state under the action of the deformation and magnetic field is determined and the probability of transitions between levels is estimated. Using the... (Read more)

I. Introduction (p.258): II. Emprical Properties (p.261): 1. Energy Levels (p.261), a. Ionization Energies, b. Spectra of Excited States, 2. Spin Resonance (p.266), a. Electron Spin Resonance, b. Double Resonance, 3. Static Magnetic Susceptibility (p.271), III. Structure of Donor States (p.271): 4. Conduction Bands of Silicon and Germanium (p.271), a. Silicon, b. Germanium, 5. Effective Mass Theory of Donor States (p.274), a. Single Band Minimum at k=0, b. Several Conduction Band Minima, c. Matrix Elements for Radiative Transitions, 6. Numerical Results and Comparison with Experiments (p.285), a. Energy Levels, b. Wave Functions, 7. Corrections to the Effective Mass Formalism (p.289), a. General Considerations, b. Corrected Wave Functions, c. Comparison with Experiment, IV. Structure of Acceptor States (p.297): 8. Valence Bands of Silicon and Germanium (p.297), a. Silicon, b. Germanium, 9. Effective Mass Equations for Acceptor States (p.300), 10. Approximate Solutions and Comparison with Experiment (p.301) a. Germanium b. Silicon V.Effects of Strains and of Static Electric and Magnetic Fields (p.306): 11. Strains (p.306) a. Donor States, b. Acceptor States, 12. Stark Effect (p.311)