Possible Role of Hydrogen within the So-Called X Center in Semi-Insulating 4H-SiC

Abstract

Multi-frequency electron paramagnetic resonance (EPR) measurements between 9 and 140 GHz as well as Hall measurements were performed on a series of nominally undoped high-purity semi-insulating (HPSI) 4H-SiC. The investigations in a temperature range from 4 K to 300 K were focused on the photosensitive intrinsic X-defect residing at two inequivalent lattice sites (X h and X k ). Photo-EPR and Hall effect measurements indicate donor-like energy levels at 1.26 ± 0.06 eV and 1.36 ± 0.06 eV below the conduction band for X h and X k , respectively. The EPR spectra recorded at 77 K and at 9 GHz consist of superimposed EPR lines, which were characterized by axially symmetric gtensors and resolved hyperfine (hf) lines. The hf interactions determined are identical to those published earlier in two independent works for the carbon vacancy in a single positive charge state. However, it is a surprising fact that for one hf line the intensity ratio is different in all works. With the help of additional theoretical investigations, these variations are tentatively assigned to the contamination of a sample-dependent fraction of carbon vacancies with hydrogen.

Intrinsic defects in nonstoichiometric β-SiC nanoparticles studied by pulsed magnetic resonance methods

“…It is necessary to add that the corresponding shf constants of 29 Si for carbon vacancies in bulk SiC crystals are essentially higher [23] indicating that the wavefunction of the unpaired electron of the vacancy in np-SiC is substantially higher delocalized than in bulk material. At the same time, considering that the ENDOR spectrum of the D2 center shows a weak shf interaction with hydrogen we may suggest that the carbon vacancy environment would be contaminated with hydrogen forming the hydrogen-related defect (V C +H) with donorlike behavior [24,25]. Table 2 shows the calculated shf interaction for carbon vacancies in np-SiC and hydrogenated carbon vacancy with S = 1/2 in bulk SiC calculated in the framework of density functional theory (DFT) in [25] along with experimental shf interaction observed for D2 and DII center.…”

Identification and Kinetic Properties of the Photosensitive Impurities and Defects in High-Purity Semi-Insulating Silicon Carbide

“…The thickness of the illuminated sample was about 35 m, which was thin enough for the light to illuminate the total sample. The PPC data obtained by optical admittance spectroscopy at T = 300 K were taken from (Kalabukhova et al, 2006). The technique employed in optical admittance spectroscopy measurements was described in considerable detail in (Evwaraye et al, 1995).…”

“…EPR parameters of the X c and X h defects with S = 1/2 in HPSI 4H-SiC samples measured at T = 77 K. A  and A  are the HF splitting as determined from angular dependent EPR measurements. The number of magnetic nuclei determined from the relative intensities of the HF satellites is given after (Kalabukhova et al, 2006) for X c /X h , after (Konovalov et al, 2003) for ID1/ID2 and after (a, b. Umeda, et al, 2004;Bockstedte et al, 2003) for E15/E16 centers residing c/h positions. 1) The lines are labeled after Fig.…”

“…As was seen from Table 2, the energy level of the 0 / C V  in contrast to the X-defect is pinned in the lower half of the band gap and shows acceptor-like behavior. Therefore, the X-defect which shows the donor-like behavior was assigned to the hydrogenated carbon vacancy (V C +H) 0/-which occupies the c and h positions in the 4H-SiC lattice (Kalabukhova et al, 2006). In accordance with calculations performed in (Aradi et al, 2001;Gali et al, 2003), the most stable configuration of the (V C +H) 0/-is that where hydrogen is built in bond-bridging between two Si-ligands of V C as was shown in Fig.…”

“…At the same time, investigation of the role, which they play in the trapping, recombination, and ionization of non-equilibrium charge carriers, processes of paramount importance for semiconducting materials, has not received proper attention. HPSI 4H-SiC samples have a specific feature of the so-called persistent relaxation (PR) of the photo-response and persistent photoconductivity (PPC), which originate from a very long (over 30 h) lowtemperature lifetime of photo-carriers trapped into defect and impurity levels (Kalabukhova et al, 2006). In this chapter we present the results of identification of the intrinsic defects observed in EPR spectrum of HPSI 4H and 6H-SiC wafers in the dark and under photo-excitation and investigation of the PR and PPC which form in HPSI 4H-SiC samples at low temperatures after termination of photo-excitation.…”