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Parameters of electrically active defect centres in vanadium-doped 6H silicon carbide (6H-SiC:V) were investigated by means of the photoinduced transient spectroscopy (PITS) and modulated photocurrent (MPC) method. After a short description of the two techniques, experimental results are presented and briefly compared. Our aim is mainly to understand and explain these experimental results. In particular, in the PITS technique a shallow level seems to be at the origin of negative photoconductivity. Besides, in the same temperature range hole and electron levels can be detected at the same time. Finally, the detection of a given level seems to depend on the photon flux used to perform the PITS experiment. As far as the MPC experiment is concerned, it has put into evidence a very efficient shallow level. A numerical calculation was developed to simulate both experiments in order to understand the experimental results. By means of this simulation, we have explained all the phenomena observed experimentally in each technique and we propose a simple model for the distribution of electrically active defect centres in 6H-SiC:V crystals.

Photoinduced transient spectroscopy (PITS) has been applied to study electronic properties of point defects associated with charge compensation in semi-insulating (SI) 6H-SiC substrates. The photocurrent relaxation waveforms were digitally recorded in a wide temperature range of 20–800 K and in order to extract the parameters of defect centres, a two-dimensional analysis of the waveforms as a function of time and temperature has been implemented. As a result, the processes of thermal emission of charge carriers from defect centres were seen on the spectral surface as the folds, whose ridgelines depicted the temperature dependences of emission rate for detected defect centres. The new approach was used to compare the defect levels in vanadium-doped and vanadium-free (undoped) SI 6H-SiC wafers.

PACS 61.72. Ji, 71.55.Ht Defect levels in the n-type bulk 6H-SiC have been investigated by deep level transient spectroscopy (DLTS) and photoinduced transient spectroscopy (PITS). From the DLTS spectra, four electron traps at E c -0.53 eV (T1), E c -0.64 eV (T2), E c -0.67 eV (T3) and E c -0.69 eV (T4) , respectively, were revealed. The centers T1, tentatively identified with carbon vacancies, were found to be located in the vicinity of dislocations. The centers T2 and T3 were assigned to the known deep-level defect Z 1 /Z 2 occurring both in 4H and 6H SiC polytypes. The PITS measurements revealed two shallow traps with activation energies 20 and 60 meV, as well as a deep trap at 0.66 eV. The origin of the first trap still remains unclear. The latter two traps are tentatively identified with a nitrogen atom in hexagonal site and a complex involving a boron atom and silicon antisite, respectively.