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We investigate the temperature dependence of the resistivity and Hall coefficient for heavily Al-doped p-type 4H-SiC epilayers with Al concentrations (C_Al) of > 2E19 cm^−3, which are substrates for the collectors of insulated-gate bipolar transistors. The signs of the measured Hall co- efficients (R_H) changed from positive to negative at low temperatures. For epilayers with C_Al values of < 3E19 cm^−3, a negative R_H was observed in the hopping conduction region. In contrast, for epilayers with C_Al values of > 3E19 cm^−3, a negative R_H was observed in not only the hopping conduction region but also the band conduction region, which is a striking feature because the movement of free holes in the valence band should make R_H positive. For an epilayer with C_Al of 1.8E20 cm^−3, the sign of R_H clearly changed three times in the band conduction region. Moreover, the activation energies of the temperature-dependent R_H values were similar to those of the temperature-dependent resistivity in the corresponding temperature ranges, irrespective of the conduction mechanisms (band and hopping conduction).

We measure the temperature-dependent resistivity (ρ(T)) for thick heavily Al- and Ncodoped p-type 4H-SiC samples grown by chemical vapor deposition (CVD), physical vapor transport (PVT), and solution growth (SG), and investigate their conduction mechanisms. For samples with an Al concentration (CAl) of 3.5×1019 to 1×1020 cm-3 grown by CVD, PVT, and SG, the conduction mechanisms at high and low temperatures are band and nearest-neighbor hopping (NNH) conduction, respectively. In the range CAl of 1×1019 to 3.5×1019 cm-3, on the other hand, an anomalous conduction, referred to as X conduction here, is observed between the band and NNH conduction regions for the samples grown by CVD and PVT, but not those grown by SG. One of the differences between the samples grown by CVD and PVT and those grown by SG is the off-orientation toward [11-20] of the (0001) 4H-SiC substrate. We discuss the reason for the appearance of X conduction, which appears to be consistent with dopant-concentration inhomogeneity model.

The temperature dependencies of the resistivity and Hall coefficient for heavily Al-doped 4H-SiC epilayers with Al concentration (CAl) higher than 2×1019 cm-3 were investigated. The signs of measured Hall coefficients (RH) change from positive to negative at low temperatures. For the epilayers with CAl < 3×1019 cm-3 the sign inversion occurred in the hopping conduction region, which was reported to be explicable using the model for amorphous semiconductors. For the epilayers with CAl > 3×1019 cm-3, on the other hand, the sign inversion occurred in the band conduction region, which is a striking feature, because the movement of free holes in the valence band should make RH positive. The sign-inversion temperature increased with increasing CAl, while the dominant-conduction-mechanism-change temperature was almost independent of CAl.

By inspecting the CVD growth parameters, such as the flow rates of HCl and H2 carrier gases, the pressure and the C/Si ratio, the trench filling in a high-rate mode with a high growth rate on the bottom and a relatively low growth rate on the mesa top was carried out. 4H-SiC trenches with the depths of 48 and 55 μm have been completely filled at the rates of 6.2 and 5.5 μm/h, respectively.

By mapping the source and HCl flow rates dependent growth rates, the evolving trend of a quasi-selective epitaxial growth (quasi-SEG) that growing very thin epilayer on mesa top and ensuring an extremely low risk of voids defect generation was firstly figured out on a 5-μm 4H-SiC trench. Then, basing on the acquired knowledge, a 25-μm 4H-SiC trench with an aspect ratio up to ~10 was completely filled in the quasi-SEG mode.

The conduction mechanism in heavily Al-doped or heavily Al-and N-codoped p-type 4H-SiC epilayers was investigated. In both the singly-doped and codoped samples with an Al concentration (CAl) between 4x1019 and 2x1020 cm-3, band and nearest-neighbor hopping (NNH) conductions appeared in high and low temperature ranges, respectively. The codoping of N donors makes the NNH conduction dominant at temperatures higher than in the singly-doped samples. In both the singly-doped and codoped samples with CAl between 1x1019 and 4x1019 cm-3, an unexpected conduction appeared between the regions of the band and NNH conductions.

We observe negative Hall coefficients (R H(T)) in the variable-range hopping (VRH) conduction region for heavily Al-doped p-type 4H-SiC. We have proposed a simple physical model in which the difference between the density of hopping sites for holes and the density of hopping sites for electrons under a magnetic field determines the sign of R H(T), and explained the negative R H(T) in nearest-neighbor hopping (NNH) conduction. Based on our proposed model for NNH conduction, here we propose a model in which R H(T) becomes positive when the density of localized states (g(E)) around the Fermi level (E F) increases with increasing energy (E), whereas R H(T) becomes negative when g(E) around E F decreases with increasing E. In heavily Al-doped p-type 4H-SiC where g(E) around E F is considered to decrease with increasing E, the proposed model can explain why R H(T) becomes negative in the VRH conduction region.

The effect of H2 carrier gas on the growth rate during the trench filling using CVD epitaxial growth was investigated in a wide pressure range (10∼38 kPa). It is found that, in the entire pressure range, reducing H2 flow rate can increase the filling rate (the growth rate inside trench) and the filling efficiency (the thickness ratio between epilayer on trench bottom and mesa top), which means a high productivity and a low risk of void defects. The filling rate and efficiency of ∼1.5 μm/h and ∼18 respectively was achieved at 38 kPa.

4H-SiC trenches with depths of approximately 25 μm were filled under a special condition called the quasi-selective epitaxial growth mode that showed a refill-rate of 2.1 μm/h within 12 h, using a hot-wall chemical vapor deposition (CVD) method with the assistance of HCl gas. To develop a high-rate growth mode for the 4H-SiC trench filling process, several CVD growth parameters, such as the flow rates of source gases, HCl and H2 carrier gases, their pressures, and the applied C/Si ratio, were regulated and optimized, to enhance the partial pressures of the source species in the gas phase of the CVD reactor. A refill-rate of 11.4 μm/h in 2 h was achieved, which is nearly five times faster than the initial growth.

We have observed negative Hall coefficients [R H(T)] in a nearest-neighbor hopping (NNH) conduction region in epilayers of heavily Al-doped or Al–N co-doped p-type 4H-SiC grown on n-type 4H-SiC substrates by CVD or in wafers of heavily Al–N co-doped p-type 4H-SiC fabricated by solution growth. We propose a simple physical model to explain the sign of R H(T) in NNH conduction. According to this model, R H(T) becomes positive when the Fermi level (E F) is higher than the Al acceptor level (E Al), that is, the Fermi–Dirac distribution function f(E Al) is greater than 0.5, whereas R H(T) becomes negative when E F is lower than E Al, which occurs at low temperatures. Because the dominant conduction mechanisms in heavily Al-doped or Al–N co-doped p-type 4H-SiC with Al concentrations on the order of 1019 cm−3 are band and NNH conduction at high and low temperatures, respectively, the proposed model can explain why R H(T) becomes negative at low temperatures.

Trapezoid-shape (T-S) defects on epilayer surfaces, which include two kinds of the giant step bunching (GSB), are one of killer defects for MOSFETs. We have investigated the generation mechanism of the two GSBs using "step kinetics simulator" we developed. The simulator has reproduced the behavior of the GSBs. Based on results from the simulation, we have discussed the generation mechanism of the two GSBs.

We have developed the computer simulation including cluster effect and Schwoebel effect and investigated the conditions generating GSB using the simulation. We have demonstrated that the simulation developed can reproduce GSB. We have found for the occurence of GSB that there exists a threshold value of the surplus flux rate of Si-or C-source gases not contributing to growth, which depends on the flux rate of each source gas, namely the boundary between with and without GSB. It is noted that this boundary does not depend on the off-angle of substrates. We have also found the mechanism for explaining the occurrence of wavy surface morphplogy.

The defect evolution on 90 μm-thick heavily Al-doped 4H-SiC epilayers with Al doping level higher than 1020 cm-3 was studied by tracing back to initial growth stage to monitor major dislocations and their propagations in each growth stage. Results from X-ray topography and KOH etching demonstrate that all existing dislocations on the surface of 90 μm-thick epilayer can be identified as the defects originating from substrate. In other words, there seems no new dislocation generated after a long-term growth. Nevertheless, a high density of misfit dislocation was found appearing near the substrate/epilayer interface for epilayer with Al doping level of 3.5×1020 cm-3, while misfit dislocation cannot be seen on epilayer with Al doping level of 1.5×1020 cm-3.

We investigate the transition of the conduction mechanism from band and nearest-neighbor hopping (NNH) conduction to variable-range hopping (VRH) conduction in heavily Al-doped 4H-SiC epilayers with increasing Al concentration (C Al). In a sample with C Al of 1.8 × 1020 cm−3, the dominant conduction mechanisms at high and low temperatures were band and VRH conduction, respectively, whereas in samples with lower C Al values they were band and NNH conduction, respectively, and in samples with higher C Al values VRH conduction was dominant over the entire range of measurement temperatures examined (20–600 K).

Heavily Al-doped 4H–SiC thick epilayers (∼90 μm) were grown on 3-in n + 4H–SiC wafers by using the hot-wall CVD method. On the purpose of enhancing incorporated Al-dopant concentration, the growth condition dependence of the Al incorporation behavior in the heavy doping range near Al solubility limit in 4H–SiC was investigated by varying the growth parameters, i.e ., growth rate, pressure, temperature and Al-dopant source flow rate. A series of thick epilayers possessing Al-dopant concentration from 9.6×10 19 to 4.7×10 20 cm −3 were obtained. Among them, the epilayer with Al-dopant concentration of 3.5×10 20 cm −3 demonstrates a comparably low resistivity of 16.5 mΩ cm as that of commercial n + 4H–SiC wafer. The incorporated Al-dopant concentration dependences on surface morphology, crystalline quality and crystal structures of the heavily Al-doped thick epilayers on n + 4H–SiC substrates were characterized and discussed.

By using hot-wall CVD method, thick heavily Al-doped 4H-SiC epilayers (~90 μm) were grown on 3-inches 4H-SiC wafers. Around the solubility limit, the incorporation behaviors of Al into 4H-SiC were investigated by varying the growth conditions. Among the samples having smooth surfaces, the maximum Al dopants concentration of 3.5×1020 cm-3 and the minimum resistivity of 16.5 mΩcm were achieved. The results of Hall-effect measurement demonstrate that, along with the increase of Al doping level, the activation ratio of Al dopants gradually increases from several percent up to 100% where the Al dopants concentration is 1.5×1020 cm-3.

We found that the ‘Si and C emission model’ that we proposed as an oxidation model of SiC could not reproduce the initial oxide growth rates of SiC at sub-atmospheric pressures. The comparison between calculated and observed growth rates suggests that the oxide growth on the oxide surface is enhanced in the initial oxidation stage and thus our oxidation model is inaccurate in the description on the surface oxidation. Accordingly, we reconsidered the parameters on surface oxidation and, as a result, found that a much enlarged oxygen concentration on the oxide surface is necessary for solving the discrepancy between calculated and observed growth rates.

To understand the structure of SiC–oxide interface more in detail, we propose a profiling theory of Si and C emission into SiC layer during oxidation. Simulations of the depth profiles of Si and C interstitials results in the structures analogous with those observed from a spectroscopic ellipsometry. To determine the diffusivities of Si and C interstitials, we performed capacitance–voltage measurements for examining the re-distribution profiles of nitrogen after oxidation and compared between observed and calculated profile. The calculated nitrogen profiles showed good fits to the observed ones in the case of self-diffusivity of C interstitials magnified by several 10 times for literature value. Finally, we discuss the validity of the proposed theory.

We have tried to apply the oxidation model of SiC proposed previously, termed ‘Si-C emission model’, to the oxide growth rate at various oxidation temperatures. We have found that the model well reproduces the oxide thickness dependences of oxide growth rates for all of the temperatures measured for both of the SiC Si- and C-faces. We have estimated the temperature dependence of oxide depth profiles of Si and C interstitials by using the Si-C emission model, and discussed the structure at/near the SiC–oxide interface.

In this study, we investigated the cluster effect on the occurrence of giant step bunching. We generated carbon clusters on 4H-SiC (0001) surfaces by thermal decomposition of SiC in an Ar atmosphere and controlled the surface concentrations of the clusters by adding H2 gas. We found the boundaries between surfaces with and without giant steps to show Arrhenius-type behavior. This behavior agreed with our predictions deduced from a chemical reaction model that takes the cluster effect into account, suggesting that giant step bunching is attributable to the formation of clusters on SiC.

We have investigated the oxidation process of SiC (000-1) C-face at low oxygen partial pressures using an in-situ spectroscopic ellipsometry. The oxide growth rate decreased steeply at the early stage of oxidation and then slowly decreased with increasing oxide thickness. The initial oxide growth rate was almost proportional to the oxygen partial pressure for both the polar directions. This result suggests that the initial interfacial reaction rate is constant regardless of the concentration of oxidants reaching the interface.

4H-SiC–oxide interfaces formed by various oxidation methods on SiC (0 0 0 1) Si- and ( 0 0 0 1 ¯ ) C-face substrates have been characterized by performing spectroscopic ellipsometry in wide spectral region including deep UV spectral range and capacitance–voltage measurements. The results exhibit that the refractive indices of the interface layers well correlate with interface state density in all the cases of oxidation processes. To investigate the difference in interface characteristics between wet and dry oxidation, we compared to the sample fabricated by wet oxidation followed by heating in Ar or O2 atmosphere, aiming to remove hydrogen related species at the interface. We also tried to make clear the difference in the interface characteristics between Si- and C-faces by lowering the oxidation rate of C-face down to those for Si-face. Putting together with all of the results obtained, we discuss the origins that determine the interface characteristics in terms of both the optical and electrical characterizations.

Thermal oxidation process of silicon carbide in ultra-thin oxide regime has been studied by performing in-situ and real time spectroscopic ellipsometry. We found the thermal oxidation at 700°C forms no or extremely thin interface layers between SiC and oxide layers. In contrast, the oxidation at 850°C forms an interface layer of around 1 nm in thickness, having similar thickness and optical constants of the interface layers formed by the oxidation at higher temperature than 1000°C. To make clear the conditions no interface layer is formed, i.e., whether low temperature growth or thin oxide thickness is crucial, we have performed the oxidation at 850°C in the reduced oxygen pressure. Based on the results of these experiments, we discussed the origin of the formation of interface layers as well as the oxidation mechanism of SiC.

We proposed a kinetic model for SiC oxidation, named ‘silicon and carbon (Si-C) emission model’, taking into account the emission of Si and C atoms from the SiC–oxide interface, which suppresses the oxidation rate at the interface. Based on the model, we calculated oxide growth rates for SiC (0001) Si- and (000–1) C-face and found that the calculated values exhibit good fits to the measured ones in the entire oxide thickness range for both faces. We also calculated depth profiles of Si and C interstitials and oxidants, and discussed the oxidation mechanism of SiC as well as the difference in the oxidation process of Si-face and C-face.

We have characterized 4H-SiC–oxide interfaces fabricated by thermal oxidation of SiC using spectroscopic ellipsometry in the wide spectral range from visible to deep UV region. It was found that there exists an interface layer, around 1 nm in thickness, regardless of the oxide thickness from 15 nm to 40 nm. The optical constants of the interface layer have similar spectral dependence to those of SiC, though the absolute value of the refractive indices is 0.5–1 larger than that of SiC. We have discussed the structure of the interface layer based on the oxidation mechanism of SiC, like the Si-emission model.

Thermal oxidation process of silicon carbide (SiC) has been studied by performing in-situ spectroscopic ellipsometry. In our previous work, we, for the first time, found that the growth rates of SiC(000 (1) over bar) C-face at oxidation thicknesses less than around 20 nm are much higher than those given by the Deal-Grove (D-G) model. In this report, we show that such a growth rate enhancement occurs also in the oxidation of SiC(0001) Si-face. By applying the empirical equation proposed by Massoud et al. [J. Electrochem. Soc. 132 (1985) 2685] to the oxidation of SiC Si-face and comparing the temperature and oxygen partial pressure dependences of oxidation rate parameters obtained with those for C-face, we discuss the difference in oxidation mechanism between SiC Si- and C-faces. [DOI: 10.1143/JJAP.47.7803]

To explain the growth rate enhancement of SiC oxidation in the thin oxide regime, which was recently found from the real time monitoring experiments of the initial oxidation stage of SiC (000–1) C-face using an in-situ spectroscopic ellipsometer, we tried to apply the interfacial Si emission model, which has been originally proposed for Si oxidation, and found that the Si emission model successfully reproduced the SiC oxidation rates at the whole range of oxide thickness and at oxidation temperatures measured. By comparing with the simulations for Si oxidation, we have discussed the oxidation mechanism of SiC.

To elucidate the origin of giant step bunching on 4˚ off-axis 4H-SiC (0001) faces, we carried out hydrogen etching and epitaxial growth under various conditions. We found that giant step bunching occurs during hydrogen etching and epitaxial growth at extremely low or high C/Si ratios, i.e., with an excessive supply of SiH4 or C3H8. From these results, we have proposed that the origins of giant step bunching are asymmetry in the step kinetics in etching and Si or C cluster generation on terraces during growth.

Real time observations of SiC (000–1) C-face and (0001) Si-face oxidation were performed using an in-situ ellipsometer over the oxygen-partial-pressure range from 0.1 to 1.0 atm. We analyzed the relations between oxide growth rate and oxide thickness by applying an empirical relation proposed by Massoud et al. We found the occurrence of oxidation enhancement in the thin oxide regime also for Si-face as well as for C-face. We have discussed the oxygen-partial-pressure dependence of the oxidation rate constants between SiC C- and Si face, comparing with that of Si.

We have simultaneously determined the carrier concentration, mobility, and thickness of 4H-SiC homo-epilayers with carrier concentration of 1016–1018 cm-3 from reflectance spectroscopy in the wavenumber range of 20–2000 cm-1. The spectra at 20–100 cm-1 and at 80–2000 cm-1 were measured by using the terahertz time domain spectrometer (THz-TDS) and the Fourier-transform infrared (FTIR) spectrometer, respectively. A modified classical dielectric function (MDF) model was employed for the curve fitting. We have compared the values of free carrier concentrations estimated from the reflectance spectroscopy with the net doping concentrations obtained from C–V measurements, and have discussed the validity of the electrical properties estimated from the reflectance spectroscopy.

We have studied photoluminescence spectra in detail to clarify the character of the isoelectronic traps in dilute GaAsN alloys. Several sharp lines have been observed at the lower energy side of the GaAs bandgap and are in good agreement with the nitrogen pair-related emission lines previously reported. In addition to the nitrogen pair-related lines, some other emission lines have been also observed. Compared with the energies of these emission lines and the nitrogen pair-related emission lines, it was found that the energy differences agree with the longitudinal optical phonon energy at the Γ point of GaAs, showing that the character of isoelectronic traps due to nitrogen pairs in dilute GaAsN alloys is significantly contributed from the conduction band state at the Γ point. The temperature dependence of the peak energy of luminescence due to nitrogen pairs also indicates that the character of isoelectronic traps in dilute GaAsN alloys is due to the conduction band edge state at the Γ point of GaAs. For a dilute GaAsN alloy with lower nitrogen concentration, we have observed that the intensity of an emission line increased superlinearly with excitation power . (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

InN/In 0.83 Ga 0.17 N multiple quantum well (MQW) structures have been fabricated on 3C–SiC (0 0 1) substrates by radio-frequency plasma-assisted molecular beam epitaxy (RF-MBE). The surface morphology, structural properties, and optical properties of the samples were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and photoluminescence (PL), respectively. XRD satellite peaks due to the periodic structure were clearly observed in the MQW structures grown at temperatures lower than 530 °C. PL emissions from the MQW were observed around 0.85 eV.

a -Plane InN films were grown on r -plane sapphire substrates with GaN underlayers by RF-N 2 plasma molecular beam epitaxy (MBE). X-ray diffraction (XRD) measurements and reflection high-energy electron diffraction (RHEED) observation revealed that the InN films were grown with InN (1 1 2¯ 0)∥GaN (1 1 2¯ 0)∥sapphire (2 2¯ 0 4). We have carried out micro-Raman scattering measurements for a -plane InN film. Raman peaks were observed at 448, 490 and 598 cm −1 , which can be identified as the A 1 transversal optical (TO), E 2 (high) and E 1 longitudinal optical (LO) mode phonon, respectively. We also carried out photoluminescence (PL) measurements for a -plane InN film. Strong PL was observed between 0.62 and 0.65 eV, which is the lowest ever reported for InN. It is suggested from the excitation intensity and temperature dependence of the PL spectra that the red shift of the PL peak is due to the Franz–Keldysh effect.

We have used in situ micro-Raman spectroscopy to clarify the mechanism of the luminescence efficiency improvement of GaAsN alloys by laser irradiation. Raman peak intensity of GaAs-like longitudinal optical (LO) mode phonon was observed to increase with the laser irradiation time. With increasing laser power density, the Raman intensity of GaAs-like LO mode phonon was found to increase more rapidly and to be saturated in a shorter time. Changes in the Raman intensity can be expressed by the same equation used for the luminescence efficiency improvement. Time constants of changes in the Raman intensity were almost in agreement with those of the luminescence efficiency improvement. This indicates that the increase in Raman intensity of GaAs-like LO phonon is closely related to the luminescence efficiency improvement.

We have simultaneously determined the carrier concentration, mobility, and thickness of 4H–SiC homoepilayers with carrier concentrations of 10 17 –10 18 cm � 3 from infrared reflectance measurements with the wave number range of 80 – 2000 cm � 1 .A modified classical dielectric function model was employed for the fitting analyses. We have prepared n-type epilayers on p-type and n-type substrates for comparison with the values of the carrier concentration and mobility estimated from infrared reflectance measurements with those obtained from Hall-effect measurements and C–V measurements. Through these comparisons, we have confirmed the validity of the values estimated from infrared reflectance measurements. [DOI: 10.1143/JJAP.45.L1226]

Real time observation of SiC oxidation was performed using an in-situ ellipsometer over the temperature range from 900°C to 1150°C. The relations between oxide thickness and oxidation time were obtained precisely by virtue of the real time measurements. We analyzed the relations between oxide thickness and oxidation time by applying the Deal and Grove model to obtain the linear and parabolic rate constants. Taking advantage of in-situ measurements, we successfully obtained the oxidation rate constants with high accuracy.

We have proposed a novel model of hydrogen etching of SiC based on thermal equilibrium and have confirmed the validity of our model through the analysis of H2 etching experiments. The experimental results obtained showed that the etching rate is expressed by a linear equation with the H2 flow rate, by an exponential function with the reciprocal of the temperature and by a power law with the pressure. These results agree well with the theoretical behaviors derived from our model.

SiC-Oxide interfaces on 4H-SiC epitaxial substrates of various off-angles have been characterized by C-V measurements, synchrotron radiation excited photoemission spectroscopy and atomic force microscopy. We found that the interface state density (N it ) and the amount of sub-oxides (S i ) for small off-angle substrates were smaller than those for large off-angle ones. It was also found that there is a good correlation between the amount of the interface states and that of sub-oxides. Step-terrace structures were clearly observed in the surface morphology after the removal of oxide layers for small off-angle substrates, which shows that the interfaces were atomically smooth. These results suggest that the small N it and S i values for small off-angle substrates relate to the smoothness of the interface and that high performance SiC MOS devices are expected by using small off-angle substrates.

The difference between atmospheric pressure (AP)CVD and low pressure (LP)CVD in 3C-SiC heteroepitaxial growth on Si(001) surfaces has been investigated. It is found that the difference in the growth mode results in a difference in the secondary nucleation rate. It is suggested that the increase of the secondary nucleation rate causes 2D island growth on (111) faces, and that these 2D islands play an important role in the process of elimination of planar defects. A simulation of the homogeneous chemical reaction in the gas phase suggests that the origin of the difference in the secondary nucleation rate can be attributed to the difference in the mole fraction of atomic hydrogen.

Cubic InN films have been grown on MgO substrates with cubic GaN underlayers by RF-N2 plasma MBE. By changing the growth conditions, we clarified the growth temperature and In flux dependence of the quality of cubic InN films. It was found the surface of cubic InN films grown at relatively higher temperatures was smooth and that the hexagonal phase content in the InN films decreased with increasing In flux. Based on the findings, we have successfully obtained a c-InN film with high phase-purity and a smooth surface. We have carried out micro Raman scattering measurements for the high-quality cubic InN film. Raman peaks were clearly observed at 596 cm–1 and 467 cm–1, which are attributed to longitudinal optical and transverse optical phonon modes of cubic InN, respectively. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We have investigated the excitation power density and nitrogen concentration dependence of the changes in the radiative efficiency of GaAsN alloys to examine the mechanism of the photo-induced improvement of radiative efficiency. With increasing excitation power density, the radiative efficiency increased more rapidly. The measure of the improvement Iafter/Ibefore superlinearly increased with increasing nitrogen concentration x up to ∼1%. This suggests that the nonradiative recombination centers eliminated by photoexcitation are not defects formed by a single nitrogen atom but complexes formed by gathering of several nitrogen atoms. Micro Raman study revealed that the GaAs-like LO mode phonon peak intensity increased with photoexcitation time in a similar way to the increase in the radiative efficiency. Considering that this phenomenon is in a time scale of several seconds, the photo-induced structural changes correspond not to long range inter-diffusion but to local changes in atomic configuration which lead to the decrease in the density of nonradiative recombination centers. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Thermal oxide films on SiC epitaxial (000-1) C-faces have been characterized by angle-resolved photoemission spectroscopy (AR-PES). The structure of wet oxide/SiC C-face interface was compared with that of dry oxide/SiC C-face, as well as that of dry oxide/SiC Si-face, in order to clarify why a MOS device of SiC C-face achieved good electrical properties. The improvement in electrical properties was confirmed by AR-PES measurements, evidencing differences in binding energy between SiC and the Si4+ components in Si2p and valence band region, and in binding energy between SiC and the CHx components in C1s. The reason for the improvement in electrical property of MOS devices by use of SiC C-face are discussed in terms of depth profiles of oxide films calculated from the AR-PES results.

We have grown hexagonal InN (h-InN) films on 3C-SiC (001) substrates by RF-N2 plasma molecular beam epitaxy taking account of small lattice mismatch between h-InN (10-10) and 3C-SiC (110). It was found from X-ray diffraction (XRD) measurements that h-InN grows with h-InN (0001) || 3C-SiC (001) and h-InN (1-100) || 3C-SiC (110). XRD measurements also revealed that the h-InN epitaxial layers grown on 3C-SiC (001) are composed of single domain. Strong and sharp photoluminescence from the h-InN was clearly observed at around 0.69 eV. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The effect of post-oxidation annealing in Ar atmosphere (Ar POA) on 4H-SiC–oxide interfaces has been studied by capacitance to gate-bias voltage (C–V) measurements and photoemission spectroscopy (PES). It was found from the C–V measurements that the shift of the C–V curve disappears when the Ar POA temperature is higher than 600 °C. On the other hand, angle-resolved x-ray photoelectron spectroscopy measurements revealed that the thickness of the intermediate layers containing Si1+ oxidation states observed at the interfaces decreases abruptly when the Ar POA temperature exceeds 500 °C. In ultraviolet photoelectron spectra, O2p peaks were changed by Ar POA at temperatures higher than 600 °C, which is the temperature where the shift of the C–V curve disappears in C–V measurements. This shows that the change in O2p bonding by Ar POA is the origin of the shift observed in C–V characteristics. A model of structural changes in the interfaces by Ar POA has been proposed based on the results of PES measurements and those of C–V measurements.The effect of post-oxidation annealing in Ar atmosphere (Ar POA) on 4H-SiC–oxide interfaces has been studied by capacitance to gate-bias voltage (C–V) measurements and photoemission spectroscopy (PES). It was found from the C–V measurements that the shift of the C–V curve disappears when the Ar POA temperature is higher than 600 °C. On the other hand, angle-resolved x-ray photoelectron spectroscopy measurements revealed that the thickness of the intermediate layers containing Si1+ oxidation states observed at the interfaces decreases abruptly when the Ar POA temperature exceeds 500 °C. In ultraviolet photoelectron spectra, O2p peaks were changed by Ar POA at temperatures higher than 600 °C, which is the temperature where the shift of the C–V curve disappears in C–V measurements. This shows that the change in O2p bonding by Ar POA is the origin of the shift observed in C–V characteristics. A model of structural changes in the interfaces by Ar POA has been proposed based on the results of PES measurements a...

We have grown InN films on 3C-SiC (001) substrates with and without cubic GaN underlayers by RF-N 2 plasma MBE. It was found that, in the case of direct growth on 3C-SiC (001), hexagonal InN grows with the crystal orientation as hexagonal InN (1100)//3C-SiC (110), while, in the case of the growth on cubic GaN underlayers, cubic InN grows with the crystal orientation as cubic InN (110)//cubic GaN (110). Photoluminescence emissions from the cubic and hexagonal InN films were clearly observed at around 0.7 eV.