Isaho Kamata

Structural analysis and reduction of in-grown stacking faults in 4H–SiC epilayers

We investigated the structure of in-grown stacking faults in the 4H–SiC(0001) epilayers. The in-grown stacking faults nucleate near the substrate/epilayer interface and expand the area with increasing epilayer thickness in a triangular shape. From transmission electron microscope observation, the formation of 1c of 8H polytype was confirmed in the in-grown stacking fault area. We also investigated the dependence of in-grown stacking fault density on the epitaxial growth rate, growth temperature, and substrate surface preparation.

Epitaxial growth of thick 4H–SiC layers in a vertical radiant-heating reactor

A vertical radiant-heating reactor has been developed for thick silicon carbide (SiC) epitaxial growth, in which the susceptor and substrates are heated by radiation from the hot wall. The benefit of the heating and sample-holding method is demonstrated by improvements in the curvature of crystal bending and FWHM of X-ray ω-rocking curves followed by epitaxial growth. The typical growth rate is 13 16 μm/h at 1530 1550 C at the susceptor top under reduced pressure as low as 50 70 mbar. Low background doping at low 10 13 cm 3 (N d - N a ) was achieved, and some of the 4H SiC epilayers exhibited a high resistivity. We also succeeded in growing a 4H SiC epilayer over 240 μm-thick with minimal surface roughness. Little sigh of impurities was observed by low-temperature photoluminescence (LTPL), and no impurities (Al, B, Ti, V and Cr) exceeding I × 10 14 cm 3 were found by secondary ion mass spectroscopy (SIMS) for a 150 μm-thick 4H SiC epilayer. Thickness and doping uniformity along the gas flow of 5% and 11%, respectively, were obtained for 2-in substrates. Molten KOH etching analysis revealed that some of the micropipes were dissociated into closed core screw dislocations during epitaxial growth. The electrical performance of high-voltage devices was also demonstrated.

Structural Transformation of Screw Dislocations via Thick 4H-SiC Epitaxial Growth

In this paper, we studied the structural transformation of screw dislocations through gas-phase 4H-SiC epitaxial growth. We confirmed based on the numbers and features of etch pits on a surface after KOH treatment that some micropipes were closed in the epitaxial layer, and were divided into several elementary screw dislocations. We discuss the magnitude of Burgers vectors of micropipes in 4H-SiC substrates in relation to the number of elementary screw dislocations generated by micropipe closing. A depth analysis further revealed that most micropipe closings took place in the initial stage of epitaxial growth.

Evaluation of Free Carrier Lifetime and Deep Levels of the Thick 4H-SiC Epilayers

Correlations between the free carrier lifetime of thick, lightly-doped n-type 4H-SiC epilayers and some deep levels (the Z1/2 center, the EH6/7 center and the D1 center) were investigated. Concentrations of the Z1/2 center and the EH6/7 center correlated with the measured carrier lifetime to some extent. We have also compared the free carrier lifetime measured by time-resolved photoluminescence (TRPL) measurement and microwave-detected photoconductive decay (μ-PCD) measurement. The carrier lifetime measured by both technique was in close agreement. The carrier lifetime measured by LTPL increased at an elevated temperature of 500 K.

Annealing effects on single Shockley faults in 4H-SiC

We investigated the annealing effect on single Shockley faults (SSFs) in the SiC epitaxial layers by photoluminescence mapping in combination with high-power laser illumination. Comparing before and after annealing at 350–550°C, it became obvious that annealing results in the shrinking of the faulted area of SSFs. When high-power laser illumination is performed again on the same area annealed at 550°C, the right-angled triangular SSFs reformed into exactly the same features as those before annealing, but the isosceles triangular SSFs did not reform. The annealing temperature to start shrinking the faulted area differs according to the type of SSF.

INFRARED SPECTROSCOPY OF HYDRIDES ON THE 6H-SIC SURFACE

Hydrides on the 6H-SiC(0001) and (0001) surfaces before and after hydrogen annealing were investigated by infrared attenuated total reflection spectroscopy. The absorption bands of CH2 and CH3 were observed from the 6H-SiC(0001) and (0001) surfaces before hydrogen annealing. After hydrogen annealing, a sharp C–H stretching vibration attributable to a monohydride appeared on the 6H-SiC(0001) surface, in contrast to a sharp Si–H stretching vibration which can be observed on the 6H-SiC(0001) surface.

Infrared attenuated total reflection spectroscopy of 6H–SiC(0001) and (0001̄) surfaces

Fourier-transformed infrared attenuated total reflection (FTIR–ATR) spectroscopy was used to study the adsorbates on 6H–SiC(0001) and (0001) surfaces after chemical treatments and after heat treatments in hydrogen. We obtained clear absorption bands attributable to hydrides and oxides on the SiC surfaces. The ATR spectroscopy revealed polarity dependencies of Si–H and C–H stretch modes between the 6H–SiC(0001) and (0001). The surface Si–H bonds on 6H–SiC(0001) formed by the heat treatment in hydrogen were found to have a quite long life time against air exposure, and the heat treatment in hydrogen also produced a flat (0001) surface with ordered surface C–H bonds. The oxidation characteristics of 6H–SiC(0001) and (0001) surfaces were also studied, and we discussed the roles of surface treatments using H2O2 solution and H2SO4 solution at elevated temperature.

Si–H Bonds on the 6H–SiC(0001) Surface after H2 Annealing

The Si–H bonds on the 6H–SiC(0001) on-axis surface were investigated using Fourier-transformed infrared attenuated total reflection (FTIR-ATR). The clear absorption bands of the Si–H stretching vibrations were observed from the 6H–SiC(0001) on-axis surface after H2 annealing. The configuration of the Si–H bonds on the surface was discussed from the polarized spectra, the chemical characteristics and the electronegativities of the atoms bonded to the Si. The FTIR-ATR spectra suggested that the 6H–SiC(0001) on-axis surface after H2 annealing at 1000° C was primarily terminated by silicon monohydride with high regularity.

A 4.15 kV 9.07-m/spl Omega//spl middot/cm/sup 2/ 4H-SiC Schottky-barrier diode using Mo contact annealed at high temperature

In this letter, we report the fabrication of high-voltage and low-loss 4H-SiC Schottky-barrier diodes (SBDs) with a performance close to the theoretical limit using a Mo contact annealed at high-temperature. High-temperature annealing for the Mo contact was found to be effective in controlling the Schottky-barrier height at 1.2-1.3 eV without degradation of n-factor and reverse characteristics. We successfully obtained a 1-mm/sup 2/ Mo-4H-SiC SBD with a breakdown voltage (V/sub b/) of 4.15 kV and a specific on resistance (R/sub on/) of 9.07 m/spl Omega//spl middot/cm/sup 2/, achieving a best V/sub b//sup 2//R/sub on/ value of 1898 MW/cm/sup 2/. We also obtained a 9-mm/sup 2/ Mo-4H-SiC SBD with V/sub b/ of 4.40 kV and R/sub on/ of 12.20 m/spl Omega//spl middot/cm/sup 2/.

Investigation of Basal Plane Dislocations in the 4H-SiC Epilayers Grown on {0001} Substrates

In this paper, we investigated the density of basal plane dislocations (BPDs) in 4H-SiC epilayers grown on (0001) and (000-1). Re-polishing of the substrate surface, in-situ H2 etching and off-cut angle were found to influence the propagation of BPDs into the epilayers. The epitaxial growth on (000-1) substrates yields a relatively low density of BPDs compared to growth on (0001). The electrical characteristics of pn diodes were also investigated, and the suppressed forward degradation and high-voltage blocking performance were obtained in the use of the (000-1) epilayers.