Nitrogen doping concentration as determined by photoluminescence in 4H– and 6H–SiC

Abstract

Low-temperature photoluminescence (PL) spectroscopy is used for determination of the nitrogen doping concentration in noncompensated 4H– and 6H–SiC by comparing the intensity of nitrogen-bound exciton (BE) lines to that of the free exciton (FE), the latter being used as an internal reference. The results are compared with a previous work performed for the case of 6H–SiC only. A line-fitting procedure with the proper line shapes is used to determine the contribution of the BE and FE lines in the PL spectrum. The ratio of the BE zero-phonon lines (R0 and S0 in 6H, Q0 in 4H) to the FE most intensive phonon replica around 77 meV exhibits very well a direct proportional dependence on the doping as determined by capacitance–voltage (C–V) measurements for both polytypes. The use of fitting procedure which takes into account the real line shapes, the influence of the spectrometer transfer function, and the structure of the PL spectrum in the vicinity of the FE replica allows us determination of the N-doping concentration by PL for doping levels in the region 1014 cm−3–3×1016 cm−3 for 4H– and 1014 cm−3–1017 cm−3 for 6H–SiC. Above these levels the free-exciton related emission is not observable.

On-axis homoepitaxial growth on Si-face 4H–SiC substrates

“…The off angle of the substrates were measured by high resolution X-ray diffraction (HRXRD) using a Philips 'X-Pert' XRD setup. The doping of the epilayer was measured either by CV measurements with mercury probe or by the relative intensity of the nitrogen bound exciton (N-BE) no-phonon line and one of the free exciton (FE) lines in the low temperature photoluminescence (PL) spectrum of the near band gap (NBG) region [26]. The PL excited either by 244 nm or by 351 nm Ar + laser line was dispersed by a single monochromator on which a UV sensitive CCD camera cooled with liquid nitrogen was mounted to rapidly detect the PL spectra.…”

“…As the layer was intentionally doped, the intensity of N-BE is higher than the FE peak. For low-doped material with nitrogen concentration lower than 3×10 16 cm −3 , the relative intensity between the N-BE no-phonon line, such as Q 0 in 4H-SiC and one of the FE lines, such as I 76 the strongest phonon replica of the FE, has allowed a quantitative estimation of the doping concentration [26]. The concentration of the nitrogen for this doped layer determined by PL is 3×10 15 cm −3 .…”

SiC epitaxy growth using chloride-based CVD

“…The FE related lines will decrease when the doping increases and the determination of the nitrogen concentration can be determined from the relative intensity of the BE and FE lines [19]. The nitrogen concentration is plotted in Fig.1.b along the flow direction for the epilayers grown with the MTS and HCl approaches.…”

Calibration on wide-ranging aluminum doping concentrations by photoluminescence in high-quality uncompensated p-type 4H-SiC

“…The method has been suggested first by M. Tajima to measure the boron and phosphorus concentrations in silicon 18 and analogous approaches have been adopted for several semiconductor materials such as Ge, GaAs, and n-type 4H-and 6H-SiC. [15][16][17][19][20][21][22] In addition, PL probes much smaller area of the sample than other conventional methods (determined by the size of the exciting-laser spot on the sample, typically ∼100 µm), which provides possibility for mapping the doping homogeneity.…”

“…[12][13][14] Quantitative determination of the nitrogen doping concentration [N] using PL in uncompensated n-type 4H-and 6H-SiC has also been reported. [15][16][17] Quantitative determination of shallow impurities in silicon is known for a long time and is based on the fact that the ratio of the integrated PL intensity of the bound to the dopant excitons (BE) to that of free excitons (FE), R = I BE /I FE , is uniquely proportional to the doping concentration. 18 Thus, the doping concentration can be estimated from the PL spectrum by acquiring the intensity ratio.…”