Influence of carrier freeze-out on SiC Schottky junction admittance

Abstract

Special Issue Paper 235 INTRODUCTIONSilicon carbide is a very promising semiconductor for high-power, high frequency and high temperature applications. 1-3 One of the interesting features that distinguishes SiC from traditional narrow bandgap semiconductors, such as for example silicon, is that common doping impurities in SiC have activation energies which are larger than k B T at room temperature. This results in a nonzero occupation number for such impurities, and leads to various effects related to impurity ionization and neutralization when the impurity quasi-Fermi level position changes, for example due to a change in an applied bias. The situation is also complicated by the existence of inequivalent lattice sites with different parameters for the same impurity species in many, e.g., 4H and 6H, SiC polytypes. (Because the crystalline lattice of these polytypes is not a Bravais lattice and does not possess full hexagonal symmetry.) Additionally, for such imIncomplete impurity ionization is investigated in the case of nitrogen donors and aluminum and boron acceptors in 4H and 6H SiC. We calculate the degree of ionization for these impurities residing on different lattice sites in a broad temperature range and for different impurity concentrations. It is shown that the degree of carrier freeze-out is significant in heavily N-doped 6H SiC and in Al-and B-doped SiC. Using the general Schottky junction admittance model we calculate the temperature and frequency dependencies of the junction admittance in the case when impurity ionization by the applied ac bias is present. It is shown that admittance frequency dispersion may be significant at room temperature in the case of N-and B-doped SiC. Finally, we calculate the Schottky junction capacitance as a function of the applied dc bias and simulate the doping profile, using the capacitance-voltage data. The calculated profile is shown to deviate from the actual impurity concentration profile if the impurity ionization time constant is comparable with the ac bias period, which is so for Nand B-doped SiC with certain values of the impurity activation energy and capture cross-section.

Schottky barrier inhomogeneities at the interface of few layer epitaxial graphene and silicon carbide

“…3(a) over the temperature range 250 K-375 K. Measurements at lower temperatures were unreliable because of freeze-out effects in the SiC. 14 Since the Au/FLG interface is Ohmic, the rectification must arise from the FLG/SiC interface. Fig.…”

Morphology Control, Dopant Incorporation, and Selective Epitaxial Growth of 4H-SiC at Low Temperatures Using CH3Cl Growth Precursor

“…The nitrogen concentration in the C-face epilayer (Fig. However, the net free carrier concentration was found to be in excess of 2x10 20 cm -3 , which is essentially lower than the total impurity concentration of 7x10 20 cm -3 , which is a result of partial impurity activation [6] as well as incomplete dopant ionization at such high nitrogen concentration [7]. 3a) -7x10 20 cm -3 versus 1x10 19 cm -3 respectively.…”

Static and Dynamic Effects of the Incomplete Ionization in Superjunction Devices

“…It is worth noting that the cross section can be also electric field and temperature dependent. In this paper, we considered a constant value of σA (1x10 -15 cm 2 ) for boron and nitrogen doped 4H-SiC, a mean value according to several DLTS measurements reported in [25,26]. Due to the very low value of the activation energy and the doping values adopted in this study, both the dynamic and static effects of the incomplete ionization on nitrogen doped 4H-SiC could be neglected.…”