Abstract
The physical principles motivating the Z-scanning laser photoreflectance technique are discussed. The technique is shown to provide a powerful non-contact means to unambiguously characterize electronic transport properties in semiconductors. The technique does not require modeling of charge transport in the sample or a detailed theoretical model for the sample physics. Rather, the measurement protocol follows directly from the simple relation describing the radial diffusion of carriers injected by a laser source. The use of a probe laser beam permits an analytic parametrization for the Z dependence of the photoreflectance signal which depends solely on the focal parameters and the carrier diffusion length. This allows electronic transport properties to be determined with high precision using a nonlinear least squares fit procedure. The practical use of the technique is illustrated by the characterization of carrier transport properties in semiconducting p-n junctions.
Highlights
The measurement of electronic transport properties in semiconductors, namely, carrier diffusion lengths, recombination lifetimes, and mobilities, is a long standing problem in many areas of physics and engineering
It should be recognized that provided the experimental parameters are properly chosen in view of the semiconductor system under test and the physical parameters of interest, the principles of the Z-scanning LPR technique discussed here are wholly applicable to the determination of transport properties associated with any of the modulation components appearing in Eq (1)
The primary purpose of the amorphizing implant (AI) process was to reduce ion channeling during the subsequent B implant via the introduction of crystalline defects close to the sample surface
Summary
The measurement of electronic transport properties in semiconductors, namely, carrier diffusion lengths, recombination lifetimes, and mobilities, is a long standing problem in many areas of physics and engineering. Variations in local physical quantities occurring beyond the probe absorption depth cannot directly affect the PR signal Other considerations such as pump beam wavelength, intensity, and modulation frequency are important. It should be recognized that provided the experimental parameters are properly chosen in view of the semiconductor system under test and the physical parameters of interest, the principles of the Z-scanning LPR technique discussed here are wholly applicable to the determination of transport properties associated with any of the modulation components appearing in Eq (1). In the three-dimensional (3D) limit, which is encountered when tightly focused Gaussian laser sources are used, the excess carrier density involves a Hankel transform of the 1D solution and must be treated numerically.29 This exacerbates the problem of determining transport properties by requiring case-specific numerical analyses. An alternative suggestion involves holding the pump-probe offset fixed and recording the LPR phase with respect to the modulation frequency, since the LPR signal will depend on the modulation frequency due to the dependence of diffusion length on the modulation frequency. the determination of the optimal pump-probe offset for this type of measurement remains an empirical challenge
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