High-resolution Photoinduced Transient Spectroscopy of Defect Centers in Undoped Semi-Insulating 6H-SiC
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1069-D02-01
High-resolution Photoinduced Transient Spectroscopy of Defect Centers in Undoped SemiInsulating 6H-SiC Pawel Kaminski1, Roman Kozlowski1, Marcin Miczuga2, Michal Pawlowski1,2, Michal Kozubal1, and Jaroslaw Zelazko1 1 Institute of Electronic Materials Technology, ul. Wólczyñska 133, Warszawa, 01-919, Poland 2 Military University of Technology, ul. Kaliskiego 2, Warszawa, 00-908, Poland ABSTRACT High-resolution photoinduced transient spectroscopy (HRPITS) has been applied to studying defect centers controlling the charge compensation in semi-insulating (SI), vanadiumfree, bulk 6H- SiC. The photocurrent relaxation waveforms were digitally recorded in the temperature range of 50 – 750 K and a new approach to extract the parameters of defect centers from the temperature-induced changes in the time constants of the waveforms has been implemented. It is based on a two-dimensional analysis using the numerical inversion of the Laplace transform. As a result, the images of spectral fringes depicting the temperature dependences of the emission rate of charge carriers for defect centers are created. Using the new procedure for the analysis of the photocurrent relaxation waveforms and the new way of the visualization of the thermal emission rate dependences, a number of shallow and deep defect levels ranging from 80 to 1900 meV have been detected. The obtained results indicate that defect structure of undoped SI bulk 6H-SiC is very complex and the material properties are affected by various point defects occupying the hexagonal and quasi-cubic lattice sites. INTRODUCTION Semi-insulating (SI) silicon carbide is an important material in terms of manufacturing substrates for high power microwave devices and integrated circuits with GaN HEMT structures as active elements. The SI properties of SiC are achieved by compensating residual shallow level impurities such as nitrogen and boron with deep-level defects pinned the Fermi level position near the middle of the band gap. Recently, vanadium-free (undoped) SI SiC crystals with the Fermi level pinned to deep levels introduced by native defects have been widely investigated. However, the existing knowledge on the electrical activation of native defects and residual impurities in these materials is insufficient for complete controlling performance of electronic devices. The defect structure of SiC crystals is fairly complex due to the occurrence of inequivalent lattice sites for impurity atoms and intrinsic point defects. In SI 6H-SiC, the point defects can be located in three inequivalent lattice sites – the hexagonal site h and two quasicubic sites k1 and k2. Since the defect centers have different activation energies for hexagonal and cubic sites, there are a large number of energy levels in the bangap of these materials and highresolution spectroscopic techniques are necessary to fully understand the compensation mechanism. In this paper, we present new experimental results, obtained by the high-resolution photoinduced transient spectroscopy (HRPITS), on the electronic
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