Determination of the transport properties in 4H-SiC wafers by Raman scattering measurement

The free carrier density and mobility in n-type 4H-SiC substrates and epilayers were determined by accurately analysing the frequency shift and the full-shape of the longitudinal optic phono-plasmon coupled （LOPC） modes, and compared with those determined by Hall-effect measurement and that provided by the vendors. The transport properties of thick and thin 4H-SiC epilayers grown in both vertical and horizontal reactors were also studied. The free carrier density ranges between 2× 10^18 cm^-3 and 8× 10^18 cm^-3with a carrier mobility of 30-55 cm2/（V.s） for ntype 4H-SiC substrates and 1× 10^16 -3× 10^16 cm^-3 with mobility of 290-490 cm2/（V.s） for both thick and thin 4H-SiC epilayers grown in a horizontal reactor, while thick 4H-SiC epilayers grown in vertical reactor have a slightly higher carrier concentration of around 8.1×10^16 cm^-3 with mobility of 380 cm2/（V.s）. It was shown that Raman spectroscopy is a potential technique for determining the transport properties of 4H-SiC wafers with the advantage of being able to probe very small volumes and also being non-destructive. This is especially useful for future mass production of 4H-SiC epi-wafers.

Fast Homoepitaxial Growth of 4H-SiC Films on 4° off-Axis Substrates in a SiH4-C2H4-H2 System

Homoepitaxial growth of 4H-SiC epilayers is conducted in a SiH_(4)-C_(2)H_(4)-H_(2) system by low pressure hot-wall vertical chemical vapor deposition(CVD).Thick epilayers of 45μm are achieved at a high growth rate up to 26μm/h under an optimized growth condition,and are characterized by using a Normaski optical microscope,a scanning electronic microscope(SEM),an atomic force microscope(AFM)and an x-ray diffractometer(XRD),indicating good crystalline quality with mirror-like smooth surfaces and an rms roughness of 0.9 nm in a 5μm×5μm area.The dependence of the 4H-SiC growth rate on growth conditions on 4°off-axis 4H-SiC substrates and its mechanism are investigated.It is found that the H_(2) flow rate could influence the surface roughness,while good surface morphologies without Si droplets and epitaxial defects such as triangular defects could be obtained by increasing temperature.

Characterization of Obtuse Triangular Defects on 4H-SiC 4° off-Axis Epitaxial Wafers

We investigate the triangular defects with different structural features on 4H-SiC epilayers by a Nomarski micro-scope,a Candela optical surface analyzer and ultraviolet photoluminescence(UV-PL)imaging.Both the foreign particles and the substrate scratches can cause the formation of the obtuse triangular defects.The central area of some obtuse triangular defects can have the spatially confined core,in which the in-grown stacking faults can be observed under the UV-PL imaging.In contrast,the obtuse triangular defects induced by the scratches appear in the form of band-like defects,of which the width depends on the scratch direction and reaches the maximum when the scratch direction is parallel to the step flow direction.The formation mechanisms of these obtuse triangular defects are discussed.

Characterization of 4H-SiC substrates and epilayers by Fourier transform infrared reflectance spectroscopy

The infrared reflectance spectra of both 4H SiC substrates and epilayers are measured in a wave number range from 400 cm 1 to 4000 cm-1 using a Fourier-transform spectrometer. The thicknesses of the 4H-SiC epilayers and the electrical properties, including the free-carrier concentrations and the mobilities of both the 4H SiC substrates and the epilayers, are characterized through full line-shape fitting analyses. The correlations of the theoretical spectral profiles with the 4H-SiC electrical properties in the 30 cm-1-4000 cm 1 and 400 cm-1-4000 cm-1 spectral regions are established by introducing a parameter defined as error quadratic sum. It is indicated that their correlations become stronger at a higher carrier concentration and in a wider spectral region （30 cm-1-4000 cm-1）. These results suggest that the infrared reflectance technique can be used to accurately determine the thicknesses of the epilayers and the carrier concentrations, and the mobilities of both lightly and heavily doped 4H-SiC wafers.

Chloride-based fast homoepitaxial growth of 4H-SiC films in a vertical hot-wall CVD

Chloride-based fast homoepitaxial growth of 4H-SiC epilayers was performed on 4° off-axis 4H-SiC substrates in a home-made vertical hot-wall chemical vapor deposition（CVD） system using H2-SiH4-C2H4-HCl.The effect of the SiH_4/H_2 ratio and reactor pressure on the growth rate of 4H-SiC epilayers has been studied successively.The growth rate increase in proportion to the SiH_4/H_2 ratio and the influence mechanism of chlorine has been investigated.With the reactor pressure increasing from 40 to 100 Torr,the growth rate increased to 52μm/h and then decreased to 47 μm/h,which is due to the joint effect of H_2 and HC1 etching as well as the formation of Si clusters at higher reactor pressure.The surface root mean square（RMS） roughness keeps around 1 nm with the growth rate increasing to 49 μm/h.The scanning electron microscope（SEM）,Raman spectroscopy and X-ray diffraction（XRD） demonstrate that 96.7 μm thick 4H-SiC layers of good uniformity in thickness and doping with high crystal quality can be achieved.These results prove that chloride-based fast epitaxy is an advanced growth technique for 4H-SiC homoepitaxy.