The Study On The Characterization Of Nitrogen And Vanadium Doped Silicon Carbide,PVT Method

In this paper,the resistivity,UV spectrum,Raman spectrum,high resolution X-ray diffraction and Secondary Ion Mass Spectroscopy of N-doped and V-doped silicon carbide wafers were tested.The N-doped and V-doped silicon carbide wafers were distinguished.In addition,through impurity concentrations enhanced in facet region,a method is supposed to characterize the variation of vanadium doping concentration in V-doped 6H-SiC wafer.Nitrogen doped silicon carbide is yellowish brown,green and light yellow,while vanadium doped silicon carbide is colorless.Resistivity experiments show that the resistivity of N-doped silicon carbide can be as low as 10^-2Ω·cm,while that of V-doped silicon carbide can be as high as 10¹²Ω·cm.The UV spectrum were observed that corresponding carrier absorption peaks of4H,6H and 15R N-doped silicon carbide appears at 464nm and 568nm in 4H-SiC,627nm in6H-SiC,422nm and 737nm in15R-SiC respectively,while the V-doped silicon carbide appears no carrier absorption peak.Besides,strong absorption bands are observed in the infrared region（900-1400nm）of the three types of N-doped silicon carbide.The absorption bands of nitrogen doped 4H,6H and 15R polytype silicon carbide are strong in the infrared region,while for V-doped SiC,the absorption peaks related to V⁴⁺appears at 1308nm,1335nm,1345nm and 1391nm.The carrier absorption peak and change of band gap explain the cause of color in N-doped SiC and colorless in V-doped SiC.The impurity concentration in the facet region of silicon carbide synthesized by PVT method will increase significantly.The facet region of silicon carbide synthesized by N-doped can be quickly identified by color,while the facet region of vanadium doped silicon carbide can not be distinguished by color because it is colorless.The concentration variation of facet region can be used as a reference plane because of doping concentration enhancement.Furthermore,according to the relationship between the Raman spectra and carrier concentration,the Raman spectra of FTA,folded transversal optical（FTO）and folded longitudinal optical mode（FLO）are analyzed because of the impurity enhancement in faceted region of silicon carbide synthesized by PVT method.The experimental results show that the red shift of FTA mode and the blue shift of FLO mode in faceted region of N-doped 4H-SiC caused by the increase of carrier concentration compared with off-faceted region However,there is no obvious change in FTO mode.Compared with the off-faceted region,the faceted region of 6H-SiC doped with vanadium shows blue shift in FTA,FTO and FLO modes.It dues to the lattice constants of faceted and off-faceted regions of V-doped 6H-SiC change significantly compared with that of N-doped4H-SiC by HRXRD,which verifies that the increase of vanadium concentration leads to the change of lattice distortion.SIMS can directly and effectively identify the impurity element concentrations of nitrogen doped and vanadium doped SiC samples.In N-doped SiC,the concentration of nitrogen is the highest and the concentration of vanadium is lower than the detection limit(10¹⁴cm^-3);The concentration of vanadium in V-doped SiC reaches 4×10¹⁷cm^-3.In addition,the vanadium concentration in faceted region is 2.3×10¹⁶cm^-3higher than that in off-faceted region,which verified the impurity concentration enhanced in facet area.