Combined effects of Ga, N, and Al codoping in solution grown 3C–SiC

Abstract

We report on Ga-doped 3C–SiC epitaxial layers grown on on-axis (0001) 6H–SiC substrates using the vapor-liquid-solid technique and different Si1−xGax melts. The resulting samples have been investigated using secondary ion mass spectroscopy (SIMS), micro-Raman spectroscopy (μ-R) and, finally, low temperature photoluminescence (LTPL) spectroscopy. From SIMS measurements we find Ga concentrations in the range of 1018 cm−3, systematically accompanied by high nitrogen content. In good agreement with these findings, the μ-R spectra show that the Ga-doped samples are n-type, with electron concentrations close to 2×1018 cm−3. As expected, the LTPL spectra are dominated by strong N–Ga donor-acceptor pair (DAP) transitions. In one sample, a weak additional N–Al DAP recombination spectrum is also observed, showing the possibility to have accidental codoping with Ga and Al simultaneously. This was confirmed on a non-intentionally doped 3C–SiC (witness) sample on which, apart of the usual N and Al bound exciton lines, a small feature resolved at 2.35 eV comings from neutral Ga bound excitons. Quantitative analyses of the DAP transition energies in the Ga-doped and witness sample gave 346 meV for the optical binding energy of Ga acceptors in 3C–SiC against 251 meV for the Al one. The conditions for the relative observa-tion of Ga and Al related LTPL features are discussed and the demonstration of room temperature luminescence using Ga doping is done.

Splitting of type-I (N-B, P-Al) and type-II (N-Al, N-Ga) donor-acceptor pair spectra in 3C-SiC

“…4 Concerning DAP spectra involving the nitrogen donor, apart from the N-Al recombination lines, N-Ga and N-B DAP spectra have also been observed in 3C-SiC. [4][5][6][7] Concerning phosphorus, the experimental results are more scarce and only P-Al DAP spectra have recently been identified. 8 The subject of interest in this work is to analyze the discrete lines in the DAP spectra, which are due to close-pair recombination spectra.…”

“…(1) and such a fit yields a rather accurate value for hυ(R → ∞) = E g − (E D + E A ). [4][5][6][7]12 However, as mentioned above, in both type-I and type-II DAP spectra, some of the shell lines are further split into well-resolved components. This cannot be explained by Eq.…”

“…The detailed growth conditions of these two samples can be found in Ref. 7. LTPL spectra were collected at 5 K using a frequency-doubled Ar + -ion laser for excitation (λ = 244 nm).…”

“…8 The subject of interest in this work is to analyze the discrete lines in the DAP spectra, which are due to close-pair recombination spectra. [4][5][6][7][8] The analysis of these sharp (discrete) lines yields important information on the host material and the impurities. This includes the dielectric constant, 9 the van der Waals interactions, 10 and the ionization energies of the donor and acceptor species.…”

Growing 3C-SiC heteroepitaxial layers on α-SiC substrate by vapour–liquid–solid mechanism from the Al–Ge–Si ternary system

“…But B-Si or Al-Si binary melts cannot be used since they systematically lead to homoepitaxial growth even on on-axis substrates [7,8]. Ga-Si melts were also tentatively studied but the layers were shown to be n-type due to very low Ga incorporation when compared to N [9]. This is why a new route like using Al-Ge-Si ternary liquid phase is studied in this work.…”