It has been recognized that Raman scattering spectroscopy is a powerful tool to characterize SiC crystals non-destructively. We review recent significant developments in the use of Raman scattering to study structural and electronic properties of SiC crystals. The areas to be discussed in the first part include polytype identification, evaluation of stacking disorder and ion-implantation damages, and stress evaluation. The Raman scattering by electronic transitions is discussed in the second part of this article. We concentrate on the plasmon LO-phonon coupled modes whose spectral profiles are used to evaluate the carrier concentration and mobility. Anisotropic electronic properties of α-SiC and characteristics of heavily doped crystals are discussed. Semiconductor-to-metal transition and Fano interference effect are also treated.

Raman Investigation of SiC Polytypes

Power semiconductor devices are key components in power conversion systems. Silicon carbide (SiC) has received increasing attention as a wide-bandgap semiconductor suitable for high-voltage and low-loss power devices. Through recent progress in the crystal growth and process technology of SiC, the production of medium-voltage (600?1700 V) SiC Schottky barrier diodes (SBDs) and power metal?oxide?semiconductor field-effect transistors (MOSFETs) has started. However, basic understanding of the material properties, defect electronics, and the reliability of SiC devices is still poor. In this review paper, the features and present status of SiC power devices are briefly described. Then, several important aspects of the material science and device physics of SiC, such as impurity doping, extended and point defects, and the impact of such defects on device performance and reliability, are reviewed. Fundamental issues regarding SiC SBDs and power MOSFETs are also discussed.

https://iopscience.iop.org/article/10.7567/JJAP.54.040103/pdf

Material science and device physics in SiC technology for high-voltage power devices

Chemical vapor deposition (CVD) of silicon carbide (SiC) onto SiC{0001} substrates and its device applications are reviewed. Polytype-controlled epitaxial growth of SiC, which utilizes step-flow growth on off-oriented SiC{0001} substrates (step-controlled epitaxy), is proposed, and the detailed growth mechanism is discussed. In step-controlled epitaxy, SiC growth is controlled by the diffusion of reactants in a stagnant layer. Critical growth conditions where the growth mode changes from step-flow to two-dimensional nucleation are predicted as a function of growth conditions using a model describing SiC growth on vicinal {0001} substrates. Step bunching on the surfaces of SiC epilayers, nucleation, and step-dynamics are also investigated. The high quality of SiC epilayers was elucidated through low-temperature photoluminescence, Hall effect, and deep level measurements. Excellent doping controllability over a wide range was obtained by in situ doping of a nitrogen donor and aluminum/boron acceptors. Recent progress in SiC device fabrication using step-controlled epitaxial layers is presented. The intrinsic potential of SiC is demonstrated in the excellent performance of high-power, high-frequency, and high-temperature devices, which will develop novel electronics.

Step-controlled epitaxial growth of SiC: High quality homoepitaxy

Models for the electron mobility in the three most important silicon carbide (SiC) polytypes, namely, 4H, 6H, and 3C SiC are developed. A large number of experimental mobility data and Monte Carlo (MC) results reported in the literature have been evaluated and serve as the basis for the model development. The proposed models describe the dependence of the electron mobility on doping concentration, temperature, and electric field. The low-field mobility in 4H SiC is much higher than in 6H and 3C in the doping range interesting for RF power transistors (10/sup 16/ cm/sup -3/ ...10/sup 18/ cm/sup -3/), whereas the saturation velocities in the three polytypes investigated are nearly the same (slightly above 2/spl times/10/sup 7/ cm/s at 300 K). The models developed can be easily incorporated into numerical device simulators.

Electron mobility models for 4H, 6H, and 3C SiC [MESFETs]

We report on the first planar high-voltage MOSFET's in 6H-SiC. A double-implant MOS (DIMOS) process is used. The planar structure ameliorates the high-field stressing encountered by SiC UMOS transistors fabricated by other groups. Blocking mode operation of up to 760 V is demonstrated, which is nearly three times higher than previously reported operating voltages for SiC MOSFET's.

High-voltage double-implanted power MOSFET's in 6H-SiC

Experimental studies on aluminum (Al) and boron (B) implantation in 4H/6H SiC are reported; the implantation is conducted at room temperature or elevated temperatures (500 to 700 C). Both Al and B act as ``shallow`` acceptors in SiC. The ionization energy of these acceptors, the hole mobility and the compensation in the implanted layers are obtained from Hall effect investigations. The degree of electrical activity of implanted Al/B atoms is determined as a function of the annealing temperature. Energetically deep centers introduced by the Al{sup +}/B{sup +} implantation are investigated. The redistribution of implanted Al/B atoms subsequent to anneals and extended lattice defects are monitored. The generation of the B-related D-center is studied by coimplantation of Si/B and C/B, respectively. (orig.) 60 refs.

Doping of SiC by Implantation of Boron and Aluminum

Homoepitaxial growth of single crystalline 6H‐SiC layers is performed by chemical vapor deposition (CVD). 6H‐SiC substrates are grown by a sublimation technique. They have vicinal surfaces inclined 1.5° to 2° from the (0001) plane towards the [1100] direction. We report CVD growth at 1600 °C in the hydrogen‐silane‐propane gas system with nitrogen as a dopant. High quality films are achieved with growth rates of about 1.8 μm per hour. The layers are examined by optical microscopy, infrared reflection, photoluminescence, and Rutherford backscattering. For electrical characterization capacitance‐voltage and Hall measurements are performed. Unintentionally doped layers have donor concentrations in the upper 1015 cm−3 range. Electron mobilities of 370 cm2/V s at room temperature and about 104 cm2/V s at 45 K are observed. To the authors’ knowledge this is the highest mobility so far reported for 6H silicon carbide.

Chemical vapor deposition and characterization of undoped and nitrogen‐doped single crystalline 6H‐SiC

Calculation of the anisotropy of the hall mobility in n-type 4H- and 6H-SiC

We report on calculations of the anisotropy of the electron Hall mobility and its temperature dependence in n-type 6H–SiC. The model is based on the conduction band structure determined recently by a first-principle calculation. It provides explicit and easy to use analytical expressions for both drift and Hall mobilities. The calculation of the Hall mobility based on our model agrees very well with experimentally determined anisotropic Hall mobility in 6H–SiC.

https://www.appi.keio.ac.jp/Itoh_group/publications/pdf/JAP08193.pdf

Theory of the electron mobility in n-type 6H-SiC

Homoepitaxial growth of 6H-SiC layers is performed at 1600°C using propane and silane as source gases. The influence of the growth parameters, temperature and gas concentrations on the growth rate is discussed. The films are examined by structural, optical and electrical characterization techniques. Unintentionally doped layers show donor concentrations of ( N D − N A ) ≈ 3 × 10 15 cm -3 . An electron mobility of 370 cm 2 /V s at room temperature and of almost 11 000 cm 2 /V s is observed at T = 45 K.

M. Schadt

Papers

Doping of SiC by Implantation of Boron and Aluminum

Chemical vapor deposition and characterization of undoped and nitrogen‐doped single crystalline 6H‐SiC

Calculation of the anisotropy of the hall mobility in n-type 4H- and 6H-SiC

Theory of the electron mobility in n-type 6H-SiC

CVD growth and characterization of single-crystalline 6H silicon carbide