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A Gummel–Poon model for abrupt, single heterojunction Npn bipolar phototransistors is described including the effects of the dc base bias on the current and optical gains. Initially, the excess electron concentration at the emitter end of the quasineutral base is determined by matching the thermionic field emission across the emitter–base heterojunction with the diffusion current at the emitter end of the base and including the effects of optical generation. The result is used in determining the electron profile in the base from which the base charge and the electron component to the emitter and collector currents are calculated following the Gummel–Poon model. The photocurrent’s components due to optical absorption in the quasineutral base, the base–collector space charge region, and the collector region are determined taking into account the nonuniform optical generation assuming topside illumination. A comprehensive description of the recombination current components is incorporated including the effects of optical absorption on recombination. The model is then used to calculate the dc and small signal current gain and the device’s optical gain, and to examine the effects of dc biasing and the optical power level. The simulation results are compared with the available experimental results and reasonable agreement is found.

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The analysis of multiexponential capacitance transients that arise in deep-level transient spectroscopy has been examined. The method of moments, a technique that provides a reliable method for resolution of a multiexponential capacitance transient into its exponential components, has been adapted and enhanced by incorporating an initial fast Fourier transform to extract the base-line offset, and a refinement in the cutoff correction to the moments integrals which improves convergence and accuracy. In addition, the mean displaced ratio smoothing algorithm has been incorporated and shown to improve the method’s accuracy in the presence of noise. For the case where the response is not significantly convoluted with the excitation, a simplified form of the method of moments technique provides a simple and more direct determination of the exponential components. Examples of results for simulated data are provided illustrating application of the analysis. The limitations of the technique in determining the number of exponential components, their amplitudes and emission rates, and the applicability of the smoothing algorithm are discussed.