Katsuki Furukawa

Characterization of the free‐carrier concentrations in doped β‐SiC crystals by Raman scattering

LO phonon‐overdamped plasmon coupled modes in n‐type epitaxial films of β‐SiC have been measured in the carrier concentration range from 6.9×1016 to 2×1018 cm−3. The carrier concentrations and damping constants are determined by line‐shape fitting of the coupled modes and compared with the values derived from Hall measurements. The concentrations obtained from the two methods agree fairly well. The Faust–Henry coefficient determined from the fitting is 0.35. The line‐shape analysis of the coupled mode has shown that the dominant scattering mechanisms in β‐SiC are deformation‐potential and electro‐optic mechanisms.

Epitaxial growth of β-SiC single crystals by successive two-step CVD

Abstract Single-crystalline β-SiC films are grown on Si (111) substrates by chemical vapor deposition (CVD) using SiH 2 Cl 2 and C 3 H 8 gases. In order to achieve the heteroepitaxial growth with large lattice mismatch, a very thin layer of polycrystalline SiC is at first deposited on the substrate surface at relatively low temperature. Then, SiC single crystal films are successively grown on the thin SiC layers for 2 to 6 h at higher temperature. SiC films with the thicknesses of 0.6–4.5 μm are obtained uniformly on the Si substrate (15 × 15 mm 2 ). X-ray diffraction and reflection electron diffraction measurements reveal an excellent crystal quality and the same crystallographic orientation as the substrate.

Temperature dependence of electrical properties of non‐doped and nitrogen‐doped beta‐SiC single crystals grown by chemical vapor deposition

Electrical properties of non‐doped and nitrogen‐doped n‐type β‐SiC films grown on Si substrates have been investigated at 70–1000 K. Those of non‐doped films remarkably depend on the Si/C ratio of the source gases. The highest mobilities of non‐doped films are 510 and 1330 cm2 V−1 s−1 at 296 and 71 K, respectively. The carrier concentrations are as low as 6×1016 cm−3 even at 1000 K. Ionization energies of 34 –37 meV for nitrogen donors and 19–25 meV for unknown donors of non‐doped films are obtained. Mobilities of both non‐doped and nitrogen‐doped films are dominated by lattice scattering at high temperatures and by impurity scattering at low temperatures. Nitrogen donors strongly affect the impurity scattering.

3C-SiC p-n junction diodes

3C‐SiC p‐n junction diodes are prepared on Si substrates by chemical vapor deposition growth with appropriate impurity doping, and their current‐voltage (I‐V) and capacitance‐voltage (C‐V) characteristics are studied. I‐V curves show good rectifying characteristics with a value of 3.3 for the ideal factor n and a reverse leakage current less than 10 μA at −5 V. The junction area is approximately 0.8 mm2. The built‐in voltage is around 1.4 V by C‐V measurements.

Effect of the junction interface properties on blue emission of SiC blue LEDs grown by step-controlled CVD

Abstract 6H-SiC blue LEDs were successively fabricated on off-axis (0001) substrates by step-controlled CVD at 1500°C using SiH 4 and C 3 H 8 . LEDs on the (0001)Si face showed dominantly a pure-blue 455 nm peak corresponding to the cathodoluminescence (CL) of the p-layer, while those on the (000 1 )C face showed mainly a purple-blue 425 nm peak corresponding to the CL of the n-layer. Considering the carrier concentrations of the LEDs, electrons are expected to be injected into the p-layer and to recombine with holes in the p-layer. The effect of a thin interface layer between the n-layer and the p-layer is supposed for the (000 1 )C face, but the effect disappeared by continuous electrical driving of the LEDs and the spectra became similar to those for the (0001)Si face. Atomic disorder of the SiC layer and/or doped impurities at the junction interface probably cause the interface layer.

Electronic properties in p-type GaN studied by Raman scattering

Raman spectra from p-type GaN have been systematically studied in the hole density range of 5×1016–1×1018 cm−3. Contrary to the case of n-type samples, spectral profiles of the LO-phonon-plasmon coupled mode in p-type show no remarkable change with the hole density. Thus, precise evaluation of electrical transport parameters such as carrier density and mobility from the coupled mode profile is difficult. However, a continuum band has been observed in the low-frequency range of the spectra, becoming intense with the increase of the hole density. This band has been attributed to the inter-valence-band transition of holes, and the intensity can be used as a good measure of the hole density.

Insulated-gate and junction-gate FET's of CVD-Grown β-SiC

An insulated-gate field effect transistor (IGFET) and a junction-gate FET (JFET) of cubic silicon carbide (β-SiC) have been fabricated using chemical vapor deposition (CVD) growth on Si substrate. In order to improve the characteristics, a boron-doped p-layer is used under the n-channel layer. Both FETs show clear drain characteristics for the first time using CVD-grown β-SiC.

Analysis of temperature dependence of Hall mobility of nondoped and nitrogen‐doped β‐SiC single crystals grown by chemical vapor deposition

Temperature dependencies of Hall mobility of nondoped and nitrogen‐doped n‐type β‐SiC films have been analyzed using a conventional theoretical model. Considering acoustic, polar optical, and piezoelectric lattice scatterings, as well as ionized and neutral impurity scatterings, theoretical calculations well fitted to the experimental results are obtained at 70–1000 K. Contributions of acoustic, polar optical, and piezoelectric scatterings to the whole lattice scattering are 84%, 14%, and 2% at 300 K, respectively. Impurity compensation ratio NA/ND of nondoped films increases from 0.45 to 0.96 with increasing Si/C ratio in the source gases. Nitrogen‐doped films show constant compensation ratios of 0.25–0.30 with various doping amounts. These values are different from the previous results obtained by the analysis of temperature dependencies of carrier concentration.

Chemical vapor deposition of single-crystal films of cubic SiC on patterned Si substrates

Stacking faults of cubic SiC films grown on Si (100) were investigated by the electrolytic etching. We find an exponential reduction of the defect density with an increase of film thickness and the anisotropy in the density for the films on off‐axis Si (100) substrates. The defect reduction along the offset direction 〈011〉 is explained from the atomic step effect limiting the length of stacking faults to smaller than the equilibrium value. In addition, the defects are eliminated by controlling the film thickness and the size of the growth area using patterned substrates. Since the defects in SiC are metastable, the film thickness required for defect‐free crystal is larger than √2× the lateral dimension.

Dependence on the Schottky metal and crystal orientation of the Schottky diode characteristics of β-SiC single crystals grown by chemical vapor deposition

Schottky barrier contacts have been made on β‐SiC single crystals grown by chemical vapor deposition on Si substrates, and their capacitance‐voltage and current‐voltage characteristics are measured. Dependence of the Schottky characteristics on Si substrate orientation [(n11), n=6, 5, 4, 3, 1, and (100)] is examined. The current‐voltage characteristics of the Schottky diodes of the β‐SiC films on Si(611) and Si(411) are excellent compared with the conventional Schottky diodes on Si(100). The barrier height is determined by the pulsed capacitance‐voltage method. Capacitance‐voltage characteristics are measured by this method avoiding the effects of deep levels which are not ionized at room temperature. The dependence on the Schottky metal (Pt and Au) is examined. Both Pt‐Schottky diodes and Au‐Schottky diodes show good rectification characteristics. The barrier height of the Pt‐Schottky diodes is 1.3–1.8 eV and that of the Au‐Schottky diodes 1.0–1.6 eV, depending on the substrate orientation. For the same ...