Fermi level control and deep levels in semi-insulating 4H–SiC

Abstract

Temperature dependent Hall effect, optical admittance spectroscopy, and optical absorption measurements of semi-insulating bulk 4H-SiC are reported. Both intentionally vanadium doped material and commercial grade semi-insulating material were investigated. The carrier concentration versus inverse temperature results from Hall effect measurements up to 1000 K indicated the samples were dominated by one of two deep levels near midgap. In addition to the deep donor level of substitutional vanadium, E c Ϫ1.6 eV, we observed another level at E c Ϫ1.1 eV in some samples, indicating that levels other than the vanadium donor can pin the Fermi level in semi-insulating SiC. Optical admittance measurements on the semi-insulating material indicate the presence of levels at E c Ϫ1.73 and 1.18 eV that were previously observed in conducting samples with this technique and we attribute these levels to the same defects producing the 1.1 and 1.6 eV levels seen by Hall effect. Secondary ion mass spectroscopy measurements of dopant and impurity concentrations are reported. Even though vanadium is present in all of these samples, along with other impurities we are at present unable to definitively identify the 1.1 eV level.

Point Defects in Silicon Carbide

“…However, for semi-insulating 4H-SiC substrates, an activation energy of $1.6 eV has often been found employing temperature-dependent resistivity measurements. In addition, EPR data of such substrates showed no existence of the V 3+ signal, corroborating that the Fermi level is pinned to a deeper V-related electron state (Mitchel et al, 1999(Mitchel et al, , 2007.…”

High resistivity measurement of SiC wafers using different techniques

“…Therefore, in the case of graphite contacts, higher voltage than that for the annealed metal contacts may be needed to pass sufficient current through the sample. For the square contact arrangement away from the wafer edges, with a distance between contacts much larger than the wafer thickness, the resistivity can be evaluated using the formula (1) where is the material resistivity, I is the applied current between contacts i and j, V is the measured voltage between contacts k and l, and w is the wafer thickness.…”

New materials for radiation hard semiconductor dectectors

“…When acting as a deep acceptor, vanadium forms a level at an energy 0.8 -1.0 eV below the conduction band, with the exact energy depending on the polytype (Jenny et al 1996), and compensates the shallow donors introduced by impurities from the growth process (Schneider et al 1990). The dominant vanadium donor state has been attributed to a level at 1.6 -1.7 eV below the conduction band (Mitchel et al 1999). Many authors report a range of deep levels in conducting SiC, identified using deep level transient spectroscopy (DLTS) and optical admittance spectroscopy.…”