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We report on the analysis of a combined mid-infrared spectroscopic ellipsometry and mid-infrared optical Hall effect investigation of wurtzite structure c-plane oriented, crack-free, single crystalline, and high-Al-content AlxGa1-xN layers on 4H-SiC. For high-Al-content AlxGa1-xN, a two mode behavior is observed for both transverse and longitudinal branches of the infrared-active modes with E1 symmetry, while a single mode behavior is found for the longitudinal modes with A1(LO) symmetry. We report their mode dependencies on the Al content. We determine and discuss static and high frequency dielectric constants depending on x. From the analysis of the optical Hall effect data, we determine the effective mass parameter in high-Al-content AlxGa1-xN alloys and its composition dependence. Within the experimental uncertainty limits, the effective mass parameters are found isotropic, which depend linearly on the Al content. The combination of all data permits the quantification of the free electron density N and mobility parameters μ. [ABSTRACT FROM AUTHOR]

Using medium- and high-resolution multi-spectra fitting of deep level transient spectroscopy (DLTS), minority carrier transient spectroscopy (MCTS), optical O-DLTS and optical-electrical (OE)-MCTS measurements, we show that the EH6/7 deep level in 4H-SiC is composed of two strongly overlapping, two electron emission processes with thermal activation energies of 1.49 eV and 1.58 eV for EH6 and 1.48 eV and 1.66 eV for EH7. The electron emission peaks of EH7 completely overlap while the emission peaks of EH6 occur offset at slightly different temperatures in the spectra. OE-MCTS measurements of the hole capture cross section σp0(T) in p-type samples reveal a trap-Auger process, whereby hole capture into the defect occupied by two electrons leads to a recombination event and the ejection of the second electron into the conduction band. Values of the hole and electron capture cross sections σn(T) and σp(T) differ strongly due to the donor like nature of the deep levels and while all σn(T) have a negative temperature dependence, the σp(T) appear to be temperature independent. Average values at the DLTS measurement temperature (∼600 K) are σn2+(T)≈1×10-14 cm², σn+(T)≈1×10-14 cm², and σp0(T)≈9×10-18 cm² for EH6 and σn2+(T)≈2×10-14 cm², σn+(T)≈2×10-14 cm², σp0(T)≈1 ×10-20 cm² for EH7. Since EH7 has already been identified as a donor transition of the carbon vacancy, we propose that the EH6/7 center in total represents the overlapping first and second donor transitions of the carbon vacancy defects on both inequivalent lattice sites. [ABSTRACT FROM AUTHOR]

We carried out Heyd-Scuseria-Ernzerhof hybrid density functional theory plane wave supercell calculations in wurtzite aluminum nitride in order to characterize the geometry, formation energies, transition levels, and hyperfine tensors of the nitrogen split interstitial defect. The calculated hyperfine tensors may provide useful fingerprint of this defect for electron paramagnetic resonance measurement. [ABSTRACT FROM AUTHOR]

Motivated by recent experimental findings on the hyperfine signal of nitrogen donor (NC) in 4H and 6H SiC, we calculate the hyperfine tensors within the framework of density functional theory. We find that there is negligible hyperfine coupling with 29Si isotopes when NC resides at h site both in 4H and 6H SiC. We observe measurable hyperfine coupling to a single 29Si at k site in 4H SiC and k1 site in 6H SiC. Our calculations unravel that such Si hyperfine coupling does not occur at k2 site in 6H SiC. Our findings are well corroborated by our new electron paramagnetic resonance studies in nitrogen doped 6H SiC. [ABSTRACT FROM AUTHOR]

The early stages of InGaN/GaN quantum well growth for In-reduced conditions have been investigated for varying thickness and composition of the wells. The structures were studied by monochromated scanning transmission electron microscopy-valence electron energy loss spectroscopy spectrum imaging at high spatial resolution. It is found that beyond a critical well thickness and composition, quantum dots (width >20 nm) are formed inside the well. These are buried by compositionally graded InGaN, which is formed as GaN is grown while residual In is incorporated into the growing structure. It is proposed that these dots act as carrier localization centers inside the quantum wells. [ABSTRACT FROM AUTHOR]

By carefully controlling the surface chemistry of the chemical vapor deposition process for silicon carbide (SiC), 100 μm thick epitaxial layers with excellent morphology were grown on 4° off-axis SiC substrates at growth rates exceeding 100 μm/h. In order to reduce the formation of step bunching and structural defects, mainly triangular defects, the effect of varying parameters such as growth temperature, C/Si ratio, Cl/Si ratio, Si/H2 ratio, and in situ pre-growth surface etching time are studied. It was found that an in-situ pre growth etch at growth temperature and pressure using 0.6% HCl in hydrogen for 12 min reduced the structural defects by etching preferentially on surface damages of the substrate surface. By then applying a slightly lower growth temperature of 1575 °C, a C/Si ratio of 0.8, and a Cl/Si ratio of 5, 100 μm thick, step-bunch free epitaxial layer with a minimum triangular defect density and excellent morphology could be grown, thus enabling SiC power device structures to be grown on 4° off axis SiC substrates. [ABSTRACT FROM AUTHOR]

A technique for the measurement of the electron velocity versus electric field is demonstrated on as-grown and H-intercalated graphene. Van der Pauw, coplanar microbridge, and coplanar TLM structures are fabricated in order to assess the carrier mobility, carrier concentration, sheet resistance, and contact resistance of both epi-materials. These measurements are then combined with dynamic IV measurements to extract a velocity-field characteristic. The saturated electron velocity measurements indicate a value of 2.33 × 107cm/s for the as-grown material and 1.36 × 107cm/s for the H-intercalated material at 300 K. Measurements are taken as a function of temperature from 100 K to 325 K in order to estimate the optical phonon energy Eso of 4H-SiC by assuming an impurity scattering model. The extracted values of Eso are 97 meV for the as-grown sample and 115 meV for the H-intercalated sample. The H-intercalated result correlates to the anticipated value of 116 meV for 4H-SiC, while the as-grown value is significantly below the expected value. Therefore, we hypothesize that the transport properties of epitaxial graphene on SiC are influenced both by intercalation and by remote phonon scattering with the SiC substrate. [ABSTRACT FROM AUTHOR]

Deep levels were detected in Fe-doped n- and p-type 4H-SiC using deep level transient spectroscopy (DLTS). One defect level (EC-0.39 eV) was detected in n-type material. DLTS spectra of p-type 4H-SiC show two dominant peaks (EV + 0.97 eV and EV + 1.46 eV). Secondary ion mass spectrometry measurements confirm the presence of Fe in both n- and p-type 4H-SiC epitaxial layers. The majority of the capture process for Fe1, Fe2, and Fe3 is multi-phonon emission assisted. These three detected peaks are suggested to be related to Fe. [ABSTRACT FROM AUTHOR]

After low-energy electron irradiation of epitaxial n-type 4H-SiC with a dose of 5×1016 cm-2, the bistable M-center, previously reported in high-energy proton implanted 4H-SiC, is detected in the deep level transient spectroscopy (DLTS) spectrum. The annealing behavior of the M-center is confirmed, and an enhanced recombination process is suggested. The annihilation process is coincidental with the evolvement of the bistable EB-centers in the low temperature range of the DLTS spectrum. The annealing energy of the M-center is similar to the generation energy of the EB-centers, thus partial transformation of the M-center to the EB-centers is suggested. The EB-centers completely disappeared after annealing temperatures higher than 700 °C without the formation of new defects in the observed DLTS scanning range. The threshold energy for moving Si atom in SiC is higher than the applied irradiation energy, and the annihilation temperatures are relatively low, therefore the M-center, EH1 and EH3, as well as the EB-centers are attributed to defects related to the C atom in SiC, most probably to carbon interstitials and their complexes. [ABSTRACT FROM AUTHOR]

Donor-acceptor pair luminescence of P-Al and N-Al pairs in 3C-SiC is analyzed. The structures in the spectra corresponding to recombination of pairs at intermediate distances are fitted with theoretical spectra of type I (P-Al pairs) and type II (N-Al pairs). It is shown that in the regions chosen for fitting the line positions obey the equation hω(R)=EG-ED-EA+e2/[variant_greek_epsilon]R, where hω(R) is the energy of the photon emitted by recombination of a pair at a distance R, e is the electron charge, [variant_greek_epsilon] is the static dielectric constant, and EG, ED, and EA are the electronic band gap and the donor and acceptor ionization energies, respectively. The fits yield the values EG-ED-EA for the N-Al (2094 meV) and P-Al (2100.1 meV) cases. Using the known value of the nitrogen ionization energy, 54.2 meV, phosphorus ionization energy of 48.1 meV is obtained. Identification of the sharp lines corresponding to recombination of close pairs in the P-Al spectrum is suggested. [ABSTRACT FROM AUTHOR]

Capacitance-voltage [C(V)] measurements of metal-insulator-semiconductor-heterostructure capacitors are used to investigate the interface between silicon nitride passivation and AlGaN/AlN/GaN heterostructure material. AlGaN/AlN/GaN samples having different silicon nitride passivating layers, deposited using three different deposition techniques, are evaluated. Different interface state distributions result in large differences in the C(V) characteristics. A method to extract fixed charge as well as traps from the C(V) characteristics is presented. Rough estimates of the emission time constants of the traps can be extracted by careful analysis of the C(V) characteristics. The fixed charge is positive for all samples, with a density varying between 1.3×1012 and 7.1×1012 cm-2. For the traps, the peak density of interface states is varying between 16×1012 and 31×1012 cm-2 eV-1 for the three samples. It is concluded that, of the deposition methods investigated in this report, the low pressure chemical vapor deposited silicon nitride passivation shows the most promising results with regards to low densities of interface states. [ABSTRACT FROM AUTHOR]

AlGaN/AlN/GaN high electron mobility transistor heterostructures grown by metal-organic chemical vapor deposition have been studied by temperature dependent time-resolved photoluminescence. The AlGaN-related emission is found to be sensitive to the excitation power and to the built-in internal electric field. In addition, this emission shows a shift to higher energy with the reduction in the excitation density, which is rather unusual. Using a self-consistent calculation of the band potential profile, we suggest a recombination mechanism for the AlGaN-related emission involving electrons confined in the triangular AlGaN quantum well and holes weakly localized due to potential fluctuations. [ABSTRACT FROM AUTHOR]

Optical detection of magnetic resonance (ODMR) was used to study defects in ZnO substrates irradiated with 3 MeV electrons at room temperature. The Zn vacancy and some other ODMR centers were detected. Among these, the Zn vacancy and two other centers, labeled as LU3 and LU4, were also commonly observed in different types of as-grown ZnO substrates. The LU3 and LU4 are related to intrinsic defects and act as dominating recombination centers in irradiated and as-grown ZnO. [ABSTRACT FROM AUTHOR]

With low energy electron irradiation in the 80–250 keV range, we were able to create only those intrinsic defects related to the initial displacements of carbon atoms in the silicon carbide lattice. Radiation induced majority and minority carrier traps were analyzed using capacitance transient techniques. Four electron traps (EH1, Z1/Z2, EH3, and EH7) and one hole trap (HS2) were detected in the measured temperature range. Their concentrations show linear increase with the irradiation dose, indicating that no divacancies or di-interstitials are generated. None of the observed defects was found to be an intrinsic defect–impurity complex. The energy dependence of the defect introduction rates and annealing behavior are presented and possible microscopic models for the defects are discussed. No further defects were detected for electron energies above the previously assigned threshold for the displacement of the silicon atom at 250 keV. [ABSTRACT FROM AUTHOR]

We have implemented graphite, graphite-tantalum (Ta), and Ta growth environment to the sublimation epitaxy of aluminum nitride (AlN) and have studied development, morphological, and cathodoluminescence emission properties of AlN crystallites. Three apparently different types of crystallites form in the three different types of growth environment, which presumably manifests the relationship between crystallite-habit-type and impurities. Comparison between the cathodoluminescence spectra reveals certain dynamics in the incorporation into AlN of the main residual dopants, oxygen and carbon, when the growth environment changes. At high temperatures, in addition to Al and N2, which constitute the vapor over AlN, vapor molecules of CN, NO, Al2C, and many more can be present in the vapor from which AlN grows and both oxygen and carbon can be incorporated into AlN in varying ratios. Involving calculations of the cohesive energy per atom of such vapor molecules and also of Ta containing molecules, we have considered possible mechanisms how oxygen and carbon get incorporated into AlN and how this kinetics interferes with the growth environment. The positive effect of Ta consists in the marked reduction of residual oxygen and carbon impurities in the vapor from which AlN is growing. However, on the account of this reduction, the overall composition of the vapor changes. We speculate that during AlN nucleation stage small impurity levels may be beneficial in order to provide a better balance between the AlN crystallites development and impurity incorporation issues. We have shown that some impurity containing vapor molecules are acting as essential transport agents and suppliers of nitrogen for the AlN growth. [ABSTRACT FROM AUTHOR]

The electrical degradation of 4H–SiC PiN diodes has recently attracted much interest and is a critical material problem for high power applications. The degradation is caused by stacking faults observed as an increased forward voltage drop after forward injection operation. In this article we have combined electrical, optical, and structural techniques to study the formation and growth of the stacking faults causing degradation. We will show three different sources causing two different types of stacking fault properties. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report the results of a study of the origins of the peak near 3838 Å observed in the photoluminescence (PL) spectrum of 4H-SiC. For n[sup +]-doped 4H-SiC material, it appears as a broad peak that is shown to be related to high-level nitrogen doping, with an energy position depending on the nitrogen concentration. A similar band is observed for 6H material, displaced in energy position by the band-gap difference between the two polytypes. A sharp peak near 3838 Å in the 4H-SiC PL spectrum has a phonon structure containing localized modes. This recombination leading to this PL line is most likely associated with an isoelectronic complex defect. The present results allow a better understanding of the PL spectrum of a low-doped epilayer grown on a heavily doped substrate. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We have studied intrinsic and impurity related defects in silicon carbide (SiC) epilayers grown with fast epitaxy using chemical vapor deposition in a vertical hot-wall reactor. Using capacitance transient techniques, we have detected low concentrations of electron traps (denoted as Z[sub ½], EH6/7 and titanium) and hole traps (denoted as HS1 and shallow boron) in the n-type 4H-SiC epilayers. The concentration of intrinsic defects (Z[sub ½], EH6/7, and HS1 centers) increases with increasing growth temperature. The incorporation of shallow boron (B) decreases at higher growth temperatures, whereas the titanium (Ti) concentration is not sensitive to the growth temperature. The concentration of shallow B and Ti increases with increasing C/Si ratio. The concentration of the EH6/7 and the HS1 centers however, decreases with increasing C/Si ratio. We have also tested graphite susceptors with TaC or SiC coating and observed that the purity of the susceptor material plays a critical role in reducing the background impurity incorporation. The correlation with the carrier lifetime of these epilayers indicates that the EH6/7 and the Z[sub ½] centers may be the lifetime limiting defects in the investigated epilayers. [ABSTRACT FROM AUTHOR]

Presents a study which demonstrated the effect of vapor composition on polytype homogeneity of epitaxial silicon carbide. Utilization of the chemical vapor deposition technique; Proposed model for vapor content controlled growth; Experimental results.

Focuses on a study which determined the nitrogen doping concentration by low-temperature photoluminescence spectroscopy in noncompensated hydrogenated amorphous silicon carbide. Specific physical and electronic properties of silicon carbide; Methodology of the study; Results and discussion.

Focuses on a study which calculated the effect of photon recycling on gallium arsenide (GaAs)/aluminum GaAs double heterostructures. Photon recycling effect; Measurement of photoluminescence decay time as a function of temperature; Explanation for the observed intensity loss at high temperatures.

Presents a study which investigated the manganese acceptor level in gallium arsenide using deep-level transient spectroscopy. Measurements of the emission and capture hole of electrons; Comparison between electron capture rates obtained from space-charge techniques and from photoluminescence decay measurements; Use of the radiative electron capture of the manganese acceptor.

The crystal structure and optical properties of thick (>100 nm) AlN layers grown by hot-wall metalorganic chemical vapor deposition are characterized by infrared spectroscopic ellipsometry, cathodoluminescence, and transmission electron microscopy. The choice of substrates among the available SiC wafer polytype modifications (4H/6H) and misorientations (on-/off-axis cut) is found to determine the AlN defect interaction, stress homogeneity, and luminescence. The growth of thick AlN layers benefits by performing the epitaxy on off-axis substrates because, due to stacking faults, the propagation of threading defects in AlN layers is stopped in a narrow interface region. [ABSTRACT FROM AUTHOR]

Electron paramagnetic resonance (EPR) was used to study the annealing behavior of the positively charged carbon vacancy (EI5 center) in electron-irradiated 4H-SiC. At ∼1000 °C the EPR signal of the defect starts decreasing gradually. Clear ligand hyperfine structure is still observed after annealing at 1350 °C, while the central line can be detected after a 1600 °C anneal. A similar annealing behavior was also observed for the EI6 center suggesting that this defect may be also the positively charged carbon vacancy but at the hexagonal lattice site. [ABSTRACT FROM AUTHOR]

Examines the self-diffusion of carbon in low-doped 4H-SiC. Use of secondary ion mass spectrometry in the study; Preparation of the carbon structure by vapor phase epitaxy; Measurement of carbon concentrations versus depth profiles.

Presents a study which examined deep level defects and their role in carrier recombination processes in electron-irradiated 3C silicon carbide using photoluminescence and optically detected magnetic resonance. Principle behind the technique; Brief background on the sample material; Description of the experimental setup; Findings.

Studies the photoluminescence decay time in a series of high quality gallium arsenide (GaAs)/aluminum GaAs double heterostructure samples. Comparison of the experimentally observed decay time as a function of temperature from 100 to 700 K with a complete calculation of the radiative recombination rate; Explanation for the observed decay time; Reason for the dominance of III-V semiconductor structures as a material for optoelectronic devices and applications.

We report on the fabrication of n+3C/n-4H SiC heterojunction diodes (HJDs) potentially promising the ultimate thermal stability of the junction. The diodes were systematically analyzed by TEM, X-ray diffraction, AFM, and secondary ion mass spectroscopy, indicating the formation of epitaxial 3C-SiC crystal on top of 4H-SiC substrate with continuous interface, low surface roughness, and up to ~7×1017cm–3 dopant impurity concentration. The conduction band off-set is about 1V as extracted from CV measurements, while the valence bands of both SiC polytypes are aligned. The HJDs feature opening voltage of 1.65 V, consistent with the barrier height of about 1.5 eV extracted from CV measurement. We finally compare the electrical results of the n+3C/n-4H SiC heterojunction diodes with those featuring Si and Ge doped anodes in order to evaluate current challenges involved in the fabrication of such devices. [ABSTRACT FROM AUTHOR]

The creation of a semi insulating (SI) buffer layer in AlGaN/GaN High Electron Mobility Transistor(HEMT) devices is crucial for preventing a current path beneath the two-dimensional electron gas(2DEG). In this investigation, we evaluate the use of a gaseous carbon gas precursor, propane, for creating a SI GaNbuffer layer in a HEMT structure. The carbondoped profile, using propane gas, is a two stepped profile with a high carbondoping (1.5 × 1018 cm-3) epitaxial layer closest to the substrate and a lower doped layer (3 × 1016 cm-3) closest to the 2DEG channel. Secondary Ion Mass Spectrometry measurement shows a uniform incorporation versus depth, and no memory effect from carbondoping can be seen. The high carbondoping (1.5 × 1018 cm-3) does not influence the surface morphology, and a roughness root-mean-square value of 0.43 nm is obtained from Atomic Force Microscopy. High resolution X-ray diffraction measurements show very sharp peaks and no structural degradation can be seen related to the heavy carbondoped layer. HEMTs are fabricated and show an extremely low drain induced barrier lowering value of 0.1 mV/V, demonstrating an excellent buffer isolation. The carbondopedGaNbuffer layer using propane gas is compared to samples using carbon from the trimethylgallium molecule, showing equally low leakage currents, demonstrating the capability of growing highly resistive buffer layers using a gaseous carbon source. [ABSTRACT FROM AUTHOR]

The effect of Mg doping on the microstructure of InN epitaxial films in relation to their free-charge carrier properties has been investigated by transmission electron microscopy (TEM) and aberration corrected scanning TEM. We observe a direct correlation between Mg concentration and the formation of stacking faults. The threading dislocation density is found to be independent of Mg concentration. The critical Mg concentration for the on-set of stacking faults formation is determined and found to correlate with the switch from p- to n-type conductivity in InN. Potential mechanisms involving stacking faults and point defect complexes are invoked in order to explain the observed conductivity reversal. Finally, the stacking faults are structurally determined and their role in the reduction of the free electron mobility in highly doped InN:Mg is discussed. [ABSTRACT FROM AUTHOR]

Self-switching diodes (SSDs) were fabricated on as-grown and hydrogen-intercalated epitaxial graphene on SiC. The SSDs were characterized as zero-bias detectors with on-wafer measurements from 1 to 67 GHz. The lowest noise-equivalent power (NEP) was observed in SSDs on the hydrogen-intercalated sample, where a flat NEP of 2.2 nW/HzV2 and responsivity of 3.9 V/W were measured across the band. The measured NEP demonstrates the potential of graphene SSDs as zero-bias microwave detectors. [ABSTRACT FROM AUTHOR]

This study presents analysis of the residual strain and related surface morphology of high-Alcontent Al0 82Ga0.18N layers doped by silicon up to the level of 3 x 1019cm-3. We focus on understanding the basic mechanisms which underlie the formation of the distinct surface morphology of the Al0.82Ga0.18N:Si layers and their conductivity. We discuss the development of certain facet structure (nanopipes) within the doped layers, which is apparent at the high Si doping levels. The formation of nanopipes influences the conductivity of the layers. It is anticipated to give rise to facets with SiN-related coverage, outcompeting the incorporation of Si at substitutional donor sites in the lattice. We do not find evidence for kinetic stabilization of preferential crystallographic facets when a dopant flow of bis(cyclopentadienyl)magnesium (Cp2Mg), instead of silane (SiH4), is implemented in the doping process. [ABSTRACT FROM AUTHOR]

The temperature-dependence of free-charge carrier mobility, sheet density, and effective mass of a two-dimensional electron gas in a AlGaN/GaN heterostructure deposited on SiC substrate is determined using the THz optical Hall effect in the spectral range from 0.22 to 0.32 THz for temperatures from 1.5 to 300 K. The THz optical Hall-effect measurements are combined with room temperature mid-infrared spectroscopic ellipsometry measurements to determine the layer thickness, phonon mode, and free-charge carrier parameters of the heterostructure constituents. An increase of the electron effective mass from (0.22±0.01)m0 at 1.5 K to (0.36±0.03)m0 at 300 K is observed, which is indicative for a reduction in spatial confinement of the two-dimensional electron gas at room temperature. The temperature-dependence of the mobility and the sheet density is in good agreement with electrical measurements reported in the literature. [ABSTRACT FROM AUTHOR]

In high resistance AlN irradiated with 2 MeV electrons, an electron paramagnetic resonance (EPR) spectrum, labeled EI-1, with an electron spin S=1/2 and a clear hyperfine (hf) structure was observed. The hf structure was shown to be due the interaction between the electron spin and the nuclear spins of four 27A nuclei with the hf splitting varying between ∼6.0 and ∼7.2 mT. Comparing the hf data obtained from EPR and ab initio supercell calculations we suggest the EI-1 defect to be the best candidate for the neutral nitrogen vacancy in AlN. [ABSTRACT FROM AUTHOR]

Tungsten was incorporated in SiC and W related defects were investigated using deep level transient spectroscopy. In agreement with literature, two levels related to W were detected in 4H-SiC, whereas only the deeper level was observed in 6H-SiC. The predicted energy level for W in 3C-SiC was observed (EC-0.47 eV). Tungsten serves as a common reference level in SiC. The detected intrinsic levels align as well: E1 (EC-0.57 eV) in 3C-SiC is proposed to have the same origin, likely VC, as EH6/7 in 4H-SiC and E7 in 6H-SiC, respectively. [ABSTRACT FROM AUTHOR]

In unintentionally Si-doped AlN, the electron paramagnetic resonance (EPR) spectrum of the Si shallow donor (g=1.9905) was observed in darkness at room temperature. The temperature dependence of the EPR signal suggests that Si in AlN is a DX center with the DX- state lying at ∼78 meV below the neutral shallow donor state. With such relatively small thermal activation energy, Si is expected to behave as a shallow dopant in AlN at normal device operating temperatures. [ABSTRACT FROM AUTHOR]

Electron paramagnetic resonance was used to study semi-insulating (SI) 4H-SiC substrates doped with vanadium (V) in the range of 5.5×1015–1.1×1017 cm-3. Our results show that the electrical activation of V is low and hence only in heavily V-doped 4H-SiC, vanadium is responsible for the SI behavior, whereas in moderately V-doped substrates, the SI properties are thermally unstable and determined by intrinsic defects. We show that the commonly observed thermal activation energy Ea∼1.1 eV in V-doped 4H–SiC may be related to deep levels of the carbon vacancy. [ABSTRACT FROM AUTHOR]

Ab initio supercell calculations have been carried out to investigate the complexes of boron acceptors with carbon self-interstitials in cubic silicon carbide. Based on the calculated binding energies, the complex formation of carbon interstitials with shallow boron acceptor and boron interstitial is energetically favored in silicon carbide. These bistable boron defects possess deep, negative-U occupation levels in the band gap. The theoretical results can explain the observed activation rates in carbon-boron coimplantation experiments. [ABSTRACT FROM AUTHOR]

We report observation of recombination enhanced defect annealing in 4H–SiC detected by capacitance transient spectroscopy and low temperature photoluminescence (PL). Intrinsic defect centers, created by 160 keV electron irradiation, reduce in concentration after illumination at temperatures much lower than previously reported annealing temperatures of 400 and 800 °C. The effect is observed after both external intense above band gap laser excitation, and with recombination in a forward biased pin diode. PL measurements show that several lines, normally detected after electron irradiation, have almost or entirely disappeared by recombination enhanced annealing at room temperature. From capacitance transient measurements, the annealing enhancement is found to be largest for the HS2 hole trap, while the EH1 and EH3 electron traps also anneal out by recombination enhanced reaction but at a lower rate. [ABSTRACT FROM AUTHOR]

Shubnikov-de Haas (SdH) and Hall effect measurements performed in a temperature range between 1.8 and 275 K, at an electric field up to 35 kV m-1 and magnetic fields up to 11 T, have been used to investigate the electronic transport properties of monolayer graphene on SiC substrate. The number of layers was determined by the use of the Raman spectroscopy. The carrier density and in-plane effective mass of electrons have been obtained from the periods and temperature dependencies of the amplitude of the SdH oscillations, respectively. The effective mass is in good agreement with the current results in the literature. The two-dimensional (2D) electron energy relaxations in monolayer graphene were also investigated experimentally. The electron temperature (Te) of hot electrons was obtained from the lattice temperature (TL) and the applied electric field dependencies of the amplitude of SdH oscillations. The experimental results for the electron temperature dependence of power loss indicate that the energy relaxation of electrons is due to acoustic phonon emission via mixed unscreened piezoelectric interaction and deformation-potential scattering. [ABSTRACT FROM AUTHOR]

First-principles calculations carried out in 4H-SiC show that hydrogen may form stable complexes with substitutional nitrogen, passivating the shallow nitrogen donor. The complex is very stable with respect to isolated positive donors and negatively charged hydrogen interstitials, so reactivation is expected only at high temperature. The binding energy also increases the concentration of hydrogen, incorporated into 4H-SiC during growth or postgrowth hydrogenation. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Stress in epitaxial layers due to crystal lattice mismatch directly influences the growth, structure, and basic electrophysical parameters of epitaxial films and also to a large extent the degradation processes in semiconductor devices. In this letter, we present a theoretical model for calculating the induced lattice compression due to N doping and the critical thickness concerning formation of misfit dislocations in homoepitaxial 4H-SiC layers with different N-doping levels. For example: The model predicts that substrates with a N concentration of 3 × 10[sup 19] cm[sup -3] induce misfit dislocations when the epilayer thickness reaches ∼ 10 µm. Also, the N-doping concentration in the 1 × 10[sup 18]-1 × 10[sup 19] cm[sup -3] range yields a strain that not will cause misfit dislocactions at the substrate and epilayer interface until an epilayer thickness of 200-300 µm is reached. Supporting evidence of the induced lattice compression due to N doping have been done by synchrotron white-beam x-ray topography on samples with different N-doping levels and are compared with the predicted results from the model. [ABSTRACT FROM AUTHOR]