Observations on the electrical characterization of the heteroepitaxially grown cubic SiC
- PDF / 3,180,224 Bytes
- 13 Pages / 576 x 792 pts Page_size
- 110 Downloads / 177 Views
This paper deals with the electrical characterization of thin layers of cubic SiC, grown on (100) Si substrates. The resistivity and Hall coefficient for undoped SiC layers were measured between 10 K and 500 K. The influence of inhomogeneities on the electrical properties of the as-grown films has been established. The Hall data show a clear sign of a transition to impurity band conduction. The donor concentrations studied are in the "intermediate" range. The donor activation energy has been shown to decrease with increasing nitrogen concentration. The nitrogen concentration was measured by SIMS. The variation in nitrogen concentration is also seen in changes in the shape of the ESR spectrum. The presence of nitrogen in the intermediate concentration range is the most likely reason for the conflicting values reported for the donor ionization energy as measured by Hall and PL measurements.
I. INTRODUCTION The need for electronic devices operating at high temperature has renewed interest in the wide bandgap semiconductor, SiC. SiC has many polytypes. Among these the cubic polytype has the highest high-temperature electron mobility. Recently large area cubic SiC layers, with thicknesses of up to 50 /xm, have been grown on 2 inch diameter Si wafers. The growth technique consists of a two-step CVD process. First a thin SiC layer is formed by carbonization of the Si surface and then a SiC layer is grown on this seed.1-2 Considerable success has been reported on the utilization of the two-step CVD-grown SiC for the fabrication of electronic devices.3"5 However, the large mismatch between the lattice parameters and the thermal expansion coefficients yields imperfect SiC films. High densities of microtwins, intrinsic stacking faults, and anti-phase domains have been observed in the films.6'7 The defect density decreases for films thicker than 3 - 4 fim, but even 20 yu,m thick films have a high concentration of defects. All unintentionally doped films are n-type and the electron Hall mobilities are substantially below the experimental values obtained for bulk grown cubic SiC.8'9 The background doping and the defects in cubic SiC films limit the use of the SiC on Si technology. Improvements will come with the identification and elimination of the imperfections. The nature of the crystalline defects is well established. On the other hand, the identity of the dominant background n-type impurity is uncertain. Electron paramagnetic resonance (EPR) spectra of CVD grown SiC films10 show the same features observed
in bulk cubic SiC.11 The spectrum is attributed to nitrogen on the carbon site and it has been used to determine the neutral nitrogen concentration in SiC. The EPR spectra reported for SiC films vary. They consist of (1) spectra with well-resolved hyperfine interaction, (2) a single line with almost unresolved hyperfine interaction, and (3) a wide single line with the same electron g value. Such a variation of the EPR spectrum of a single paramagnetic impurity in silicon is known to reflect an increase in concentration,
Data Loading...
