Figure 2

SI SiC carrier dynamics measurements. (a,b) 75-fs pulses were generated with a Ti:sapphire laser at the 800-nm fundamental wavelength. Pump wavelength was converted to 355-nm by a parametric frequency converter while probe wavelength was transformed to a white light continuum by a sapphire plate. Measurement geometry is shown schematically in (c); both beams were focused (d_spot ~ 100-μm) and near perpendicular to the sample surface. Probe beam polarization could be oriented either parallel (E∥c) or perpendicular (E⊥c) to the principal “c” crystal axis. (d) The resultant bandgap model shown schematically with our highly refined spectra and cross section measurements. We deviate from previous approaches by also including the charge state of the vanadium (see “Methods” section). By imposing the conditions of energy and charge conservation, the allowable transitions for electrons (blue) and holes (red) are also shown. This model serves as the basis of the target analysis of the data from which we can determine coefficients for a coupled set of first order rate equation³². (e) Time evolution of the GTA plot for different V concentrations shows the centroid remained constant for E∥c (2.08-eV) and E⊥c (2.66-eV). (f,g) summarize the fast and slow component data as a function of V concentration and the model fit and indicates a very prompt carrier excitation on the order of the excitation pulse width. V concentration is shown in Table 1. In (g), increased decay occurred at increased V concentration until about 10¹⁶-cm⁻³. At about that concentration level, a fast-initial decay with a long tail starts to emerge and becomes dominant at a V concentration of > 7 × 10¹⁵-cm⁻³. This result suggests that the standard Shockley–Read–Hall recombination model is inadequate, particularly with high V concentrations. (h) Shows the free carrier absorption (FCA) shortly after the initial pump (∆t = 1 ps) and at late time (∆t = 7 ns) and the model fits.