Papers by Keyword: Nitrogen Donor

Abstract: We report nitrogen (N) doping of 4H-SiC by KrF excimer laser irradiation in liquid N₂. In comparison to phosphorus (P) doping performed using phosphoric acid solution, the liquid-N₂ immersion-laser doping can introduce N atoms deeper (~ 1 μm depth) into the 4H-SiC, which results in reduction of doped layer resistance by approximately 3 orders of magnitude. Doping is shown to proceed by the thermal diffusion of species, while loss of the host material from the surface by ablation takes place at the same time. Chemical analysis shows that high density carbon (C) vacancies are generated in the N doped region, which suggests enhanced diffusion of N assisted by the presence of C vacancies. pn junction diodes are formed by using the N doping technique. Turn-on voltage is ~ -3V, which is reasonable for a pn junction diode of 4H-SiC.

Abstract: EPR and ESE in nitrogen doped 4H- and 6H-SiC show besides the well known triplet lines of 14N on quasi-cubic (Nc,k) and hexagonal (Nc,h) sites additional lines (Nx) of comparatively low intensity providing half the hf splitting of Nc,k. Frequently re-interpreted as spin-forbid¬den lines, arising from Nc,k pairs and triads or resulting from hopping conductivity, only re¬cent¬ly the theoretical calculation of the corresponding g-tensors lead to a tentative model of distant NC donor pairs on inequivalent lattice sites which are coupled to S = 1 assuming a fine-struc¬ture splitting too small to be observed in the EPR and ESE experiments. In this work, we pre¬sent ESE nutation measurements confirming S = 1 for the Nx center. Analysing the nutation frequencies in comparison with that of the Nc,k (S = 1/2) spectrum as well as the line width of ESE and EPR spectra we obtain a rough estimate between 5104 cm-1 and 50104 cm-1 for the fine-structure splitting demonstrating efficient spin-coupling between nitrogen donors in 4H-SiC.

Abstract: Nitrogen (N) donors in SiC are partially deactivated either by Si+-/N+-co-implantation or by irradiation with electrons of 200 keV energy and subsequent annealing at temperatures above 1450°C; simultaneously the compensation is decreased. The free electron concentration and the formation of energetically deep defects in the processed samples are determined by Hall effect and deep level transient spectroscopy. A detailed theoretical treatment based on the density functional theory is conducted; it takes into account the kinetic mechanisms for the formation of N interstitial clusters and (N-vacancy)-complexes. This analysis clearly indicates that the (NC)4-VSi complex, which is thermally stable up to high temperatures and which has no level in the band gap of 4HSiC, is responsible for the N donor deactivation.

Abstract: The procedure of fitting the spectra associated with donor-acceptor pair luminescence arising from nitrogen-aluminum and phosphorus-aluminum pairs in 4H SiC is described in detail. We show that the fitting can be used not only for accurate evaluation of the ionization energies of the different donors and acceptors involved, but also for unambiguous determination of their lattice sites.

Abstract: We study electronic Raman scattering of phosphorus and nitrogen doped silicon carbide (SiC) as a function of temperature in the range 7K < T < 300K. We observe a series of peaks in the Raman spectra which we assign to electronic transitions at nitrogen and phosphorus donors on different lattice sites. These transitions are identified as valley orbit transitions of the 1s donor ground state. From the polarization dependence of the observed peaks, we find that all electronic Raman signals have E2-symmetry of C6v for the hexagonal polytypes (6H-SiC and 4H-SiC) and E-symmetry of C3v for 15R-SiC. We find a reduction of the intensities of all valley-orbit Raman signals with increasing temperature and ascribe this reduction to the decreasing occupation of donor states.

Abstract: Hall effect investigations taken on Si+-/N+-, C+-/N+- or Ne+-/N+-co-implanted 4H-SiC layers and deep level transient spectroscopy investigations taken on Si+-implanted 4H-SiC layers provide experimental evidence for an electrically neutral defect complex formed during the annealing process at temperatures between 1400°C and 1700°C. This defect complex consumes nitrogen donors and an intrinsic Si containing defect species (interstitial Si or Si-antisite) or Cvacancies. At our present knowledge, we favor an (NX-SiY)-complex.

Abstract: The one-valley effective-mass approximation is developed for the case of uniaxial crystals with indirect bandgap and applied to the donor states in 4H-SiC. Good agreement is found between the theory and experiments providing data on the electronic states of the shallowest nitrogen donor in 4H-SiC. The ionization energy of this donor is deduced to be 61.35 ± 0.2 meV.