Probing carbon impurities in hexagonal boron nitride epilayers

Abstract

Carbon doped hexagonal boron nitride epilayers have been grown by metal organic chemical vapor deposition. Photocurrent excitation spectroscopy has been utilized to probe the energy levels associated with carbon impurities in hexagonal boron nitride (h-BN). The observed transition peaks in photocurrent excitation spectra correspond well to the energy positions of the bandgap, substitutional donors (C B , carbon impurities occupying boron sites), and substitutional acceptors (C N , carbon impurities occupying nitrogen sites). From the observed transition peak positions, the derived energy level of C B donors in h-BN is E D $ 0.45 eV, which agrees well with the value deduced from the temperature dependent electrical resistivity. The present study further confirms that the room temperature bandgap of h-BN is about 6.42-6.45 eV, and the C N deep acceptors have an energy level of about 2.2-2.3 eV. The results also infer that carbon doping introduces both shallow donors (C B) and deep acceptors (C N) via self-compensation, and the energy level of carbon donors appears to be too deep to enable carbon as a viable candidate as an n-type dopant in h-BN epilayers.

Exploring point defects in hexagonal boron‐nitrogen monolayers

“…It should be noted here that although the energetic range supports the assignment of the 4 eV band to the C N defect, as is done in Ref. [24] or [16], the character of the excitation (from the valence band-represented here by delocalized orbitals-to the local LUMO) is different than expected, what means that a broader peak should be present in the experiment. The C B defect also gives some excited states around 4 eV, but again the character of the excitation does not support this assignment, postulated in Ref.…”

“…It is important to conclude here that the abovementioned lowest electronic transitions of about 4 eV are good candidates to explain the famous 4 eV color band appearing in numerous experiments . The excitation is in all cases localized on the defect, what should correspond to the observed sharp peak in experimental spectra.…”

“…The simulated UV-Vis spectra for single-atom substitution, vacancies, and combined substitution-vacancy defects. Oscillator strengths are presented on the intensity axis It is important to conclude here that the abovementioned lowest electronic transitions of about 4 eV are good candidates to explain the famous 4 eV color band appearing in numerous experiments [15][16][17]29]. The excitation is in all cases localized on the defect, what should correspond to the observed sharp peak in experimental spectra.…”

“…The 4.2 and 6.0 eV lines in the photocurrent excitation spectrum were attributed to the carbon replacing nitrogen (C N ) and carbon replacing boron (C B ) defects, respectively, in Ref. (see Figure 2 of this reference). The lines at about 4.1 eV with two‐phonon replicas separated by 200 meV were interpreted as an emission line from the nitrogen vacancy (V N ) to C N in Ref.…”

Origin and roles of oxygen impurities in hexagonal boron nitride epilayers

“…The energy level of substitutional oxygen, O N , has also been previously calculated and is about 0.33 eV below the conduction band. 38 Considering the energy gap difference between various calculation and measured values, 2,3,39,40 the measured value of $0.56 eV here is in a reasonable range. Based on the PL and electrical transport results, we have constructed an energy diagram in Fig.…”