Deep Levels and Compensation in High Purity Semi-Insulating 4H-SiC
- PDF / 129,173 Bytes
- 6 Pages / 595 x 842 pts (A4) Page_size
- 60 Downloads / 143 Views
0911-B06-02
Deep Levels and Compensation in High Purity Semi-Insulating 4H-SiC W. C. Mitchel1, W. D. Mitchell1, H. E. Smith1,2, W. E. Carlos3, and E. R. Glaser3 1 AFRL/MLPS, Air Force Research Laboratory, Wright Patterson AFB, OH, 45433-7707 2 University of Dayton Research Institute, Dayton, OH, 45469 3 Naval Research Laboratory, Washington, DC, 20375 ABSTRACT A study of temperature dependent Hall effect (TDH), electron paramagnetic resonance (EPR), photoluminescence (PL) and secondary ion mass spectrometry (SIMS) measurements has been made on high purity semi-insulating (HPSI) 4H-SiC crystals grown by the physical vapor transport technique. Thermal activation energies from TDH varied from a low of 0.55 eV to a high of 1.5 eV. All samples studied showed n-type conduction with the Fermi level in the upper half of the band gap. Carrier concentration measurements indicated the deep levels had to be present in concentrations in the low 1015 cm-3 range. Several defects were detected by EPR including the carbon vacancy and the carbon-silicon divacancy. PL measurements in the near IR showed the presence of the UD-1, UD-2 and UD-3 emission lines that have been found in HPSI material. No correlation between the relative intensities of the PL lines and the TDH activation energies was seen. SIMS measurements on nitrogen, boron and other common impurities indicate nitrogen and boron concentrations higher than those of individual deep levels as determined by TDH or of intrinsic defects as determined by EPR such as the carbon vacancy or the divacancy. It is determined that several different defects with concentrations greater than or equal to 1x1015 cm-3 are required to compensate the residual nitrogen and boron.
INTRODUCTION The semi-insulating properties of high purity semi-insulating (HPSI) SiC are produced by compensation of residual shallow impurities by intrinsic deep levels with activation energies near the center of the band gap rather than by transition element impurities. The thermal activation energies of these intrinsic deep levels have been reported to be in the range of 0.9 to 1.5 eV.[1,2] A variety of intrinsic defects have been observed in this material by electron paramagnetic resonance (EPR), including vacancies, antisites and complex defects.[3-5] However, it has been very difficult to correlate electronic levels from Hall effect and resistivity measurements with the defects detected by EPR. Furthermore, the donor or acceptor nature of the deep levels responsible for compensation has not been established. We report a study of a series of HPSI 4H-SiC samples using temperature dependent Hall effect (TDH) experiments, photoluminescence (PL), EPR and secondary ion mass spectrometry (SIMS). We establish that none of the defects observed by EPR have a concentration high enough to compensate residual shallow donors and acceptors from nitrogen and boron and that multiple deep levels are required to accomplish the compensation. EXPERIMENTAL DETAILS The HPSI 4H-SiC crystals in this study were grown at Cree, Inc. by the
Data Loading...
