Correlation between the step–terrace structure and the nitrogen doping variation observed on the (0001¯) facet of 4H-SiC crystals

Abstract

The variation in nitrogen doping concentration on the (0001¯) facet of 4H-SiC single crystals grown by the physical vapor transport (PVT) growth method was investigated using Raman scattering microscopy. The observed variation was well correlated with the terrace-width variation in the step–terrace structure on the facet; regions with unevenly distributed terrace-widths always showed a lower nitrogen concentration compared to those having evenly distributed terrace-widths. It was revealed by low-energy electron channeling contrast imaging that in lower nitrogen concentration regions, terraces with two dangling bonds per silicon atom at the step riser in the step-down direction always became wider. On the basis of these experimental results, the nitrogen incorporation kinetics during PVT growth of 4H-SiC crystals was discussed.

Enhanced nitrogen incorporation in the 〈112̄0〉 directions on the (0001̄) facet of 4H-SiC crystals

“…They are alternately arranged on the surface and kinematically result in different terrace widths during growth when the surface steps flow in the 〈1100〉 direction. 19) In Fig. 6(b), such an alternating terrace-width structure is demonstrated by AFM and LE-ECC images.…”

“…In the figures, brighter (darker) contrast indicates higher (lower) nitrogen concentration. The actual nitrogen concentration was estimated using a calibration curve between the nitrogen concentration determined by secondary ion mass spectrometry (SIMS) and the Raman scattering peak shift of the LOPC mode in 4H-SiC crystals; 19) the nitrogen concentrations at the darkest and brightest contrast points in Figs. 3(b) and 3(c) were estimated to be 6.8 × 10 17 and 7.1 × 10 17 cm −3 , respectively.…”

“…As for the nitrogen incorporation on the 4H-SiC (0001) facet, another important parameter is the terrace-width ratio on the facet surface as reported by Yokomoto et al 19) revealed that the (0001) facet surface was covered with two types of terrace separated by surface steps of half unit-cell height [see Fig. 6(a)], which are denoted as terraces S 1 with two dangling bonds per silicon atom at the step riser in the step-down direction (width: T 1 ) and terraces ¢ S 1 with one dangling bond per silicon atom (width: ¢ T 1 ), and that the nitrogen incorporation was enhanced when the width ratio ( / ¢ T T 1 1 ) of these two types of terrace increased (approached to unity).…”

“…They explained this terrace-width ratio dependence of nitrogen incorporation considering the correlation between the terrace-width and the diffusion length of nitrogen adatoms on the growing crystal surface. 19) On the 4H-SiC (0001) facet surface, spiral steps show alternating step spacings in the 〈1100〉 directions and interlacing structure at azimuthal directions of 〈11 20〉. [25][26][27][28] This situation is schematically illustrated in Fig.…”

“…Particularly, the relationship between nitrogen doping and the step structure on the growing crystal surface is essential for elucidating the incorporation mechanism of dopants into crystals. Recently, Yokomoto et al 19) revealed that nitrogen incorporation is enhanced in the six crystallographically equivalent 〈11 20〉 directions on the (0001) facet. This would be due to the difference in the step structure between the 〈11 20〉 directions and other directions, such as 〈1100〉.…”