Modulated photocarrier radiometric (PCR) imaging (lock-in carrierography) of multicrystalline (mc) Si solar cells is introduced using a near-infrared (NIR) InGaAs camera and a spread superband gap laser beam as an optoelectronic source at low modulation frequencies (<10 Hz) or point-by-point scanning PCR imaging with a focused laser beam at high (kilohertz) frequencies. PCR images are supplemented by quantitative PCR frequency scans and compared to NIR optical reflectance, modulated electroluminescence (MEL) and modulated photovoltage (MPV) images. Noncontact PCR imaging is controlled by the photoexcited carrier diffusion wave and exhibits very similar images to contacting MEL and MPV. Among these methods it exhibits the highest contrast and sensitivity to mechanical and crystalline defects in the substrate at lock-in image frequencies in the range of the inverse recombination lifetime in the quasineutral region (bulk).

The dependence of the photocarrier radiometric ͑PCR͒ signal on the intensity of exciting superbandgap laser radiation was investigated. It was shown that the amplitude of the PCR signal exhibits a supralinear dependence on laser intensity I 0 ␤ , with nonlinearity coefficient/exponent ␤ such that 1 Յ ␤ Յ 2. The power dependence of the amplitude is an important indicator of the photoexcited carrier recombination physics in semiconductors ranging between monopolar ͑␤ = 1͒ and bipolar ͑␤ = 2͒ limits. The study was made with laser beams of varying wavelength, power, and spotsize and with semiconductor silicon wafers with different transport parameters, especially recombination lifetime. One-dimensional and three-dimensional models of the nonlinear PCR signal dependence on ␤ vs modulation frequency were developed. It was found that the conventional linear approach using ␤ = 1 is not always consistent with experimental slopes of amplitude vs power and it may yield erroneous values of the electronic transport properties. Consideration of the fundamental and second harmonic amplitudes and phases of the PCR signal showed that the physical origin of the nonlinear dependence of the PCR amplitude on laser intensity is consistent with high-optical-injection of free-carriers in the semiconductor. The value of ␤ can also be determined by the second harmonic-to-fundamental-amplitude ratio and is controlled by the carrier relaxation time dependence on the optically injected excess diffusive photocarrier density wave.Among the physical parameters of semiconductors, the electronic transport properties, namely, carrier recombination lifetime , carrier diffusion coefficient D, and front-and rear-surface recombination velocity S 1 and S 2 , have attracted great attention in semiconductor device manufacturing. Evaluation of these parameters is essential for characterizing semiconductor wafers, for defect and contamination monitoring, and for device modeling. 1 The technique of laserinduced infrared photocarrier radiometry ͑PCR͒ is an optoelectronic carrier density-wave diagnostic method for noncontact characterization of the electronic transport properties of semiconductors. This technique is a form of quantitative dynamic photoluminescence; it relies on the detection of modulated diffuse radiative emissions from semiconductors obeying Kirchhoff's law under conditions of nearthermodynamic equilibrium of an electronic solid when the latter is optically excited by intensity-modulated laser radiation with photon energy greater than the fundamental energy gap of the material. To determine the transport properties, both amplitude and phase of the PCR signal are simultaneously recorded as functions of angular modulation frequency ͑ = 2f͒ over several orders of magnitude and then fitted to suitable theoretical models ͓either one dimensional ͑1D͒ or three dimensional ͑3D͔͒ via a multiparameter fitting procedure. 2,3 To date, PCR has been developed as a linear technique, in the sense that the amplitude of the signal depends linearly on laser po...

A two-beam photo-carrier radiometry (PCR) technique of semiconductors has been developed. The technique operates on the superposition of superband-gap and subband-gap laser beams which results in the cross-modulation of the backscattered subband-gap laser intensity by the harmonically varying free-carrier-wave density-dependent infrared absorption coefficient. A theory of this two-beam cross-modulation approach and various experimental configurations applied to the imaging of electronic contamination and defects in silicon wafers are presented. Owing to the nonlinear interaction of the two beams, the configuration revealed a new optoelectronic effect, the decrease of the residual subband-gap absorption coefficient due to the decreased carrier capture cross-section brought about by the depletion of occupied band-gap states in the presence of photons produced by radiative recombination. Quantitative values of the optoelectronic constant B associated with the rate of depletion of free-carrier capture cross-section with superband-gap intensity, as well as of I eR , the intensity of radiative recombination emissions, were obtained. These values cannot be measured by conventional PCR or other single-ended optoelectronic techniques. The theory explains the experimental dependence of electronic transport properties on the intensity of the subband-gap beam and accounts for optoelectronic imaging contrast amplification in contaminated or defect semiconductors. The two-beam cross-modulation PCR was further shown to enhance the imaging contrast of a certain electronic contamination type (Fe in p-Si). A dramatic phase contrast enhancement of subsurface defects made by low-dose proton implantation was demonstrated at superband-gap laser intensity levels one order of magnitude lower than possible with single-ended optoelectronic imaging methodologies. This is tentatively attributed to relatively low-injection trap-filling well below optoelectronic trap saturation.

Industrial n-type Si wafers ͑resistivity of 5-10 ⍀ cm͒ were H + ion implanted with energies between 0.75 and 2.00 MeV, and the electronic transport properties of the implanted layer ͑recombination lifetime, carrier diffusion coefficient, and front-surface and implanted-interface recombination velocities s 1 and s 2 ͒ were studied using photocarrier radiometry ͑PCR͒. A quantitative fitting procedure to the diffusing photoexcited free-carrier density wave was introduced using a relatively simple two-layer PCR model in lieu of the more realistic but substantially more complicated three-layer model. The experimental trends in the transport properties of H +-implanted Si layers extracted from the PCR amplitude and phase data as functions of implantation energy corroborate a physical model of the implanted layer in which ͑a͒ overlayer damage due to the light H + ions decreases with increased depth of implantation at higher energies, ͑b͒ the implanted region damage close to the interface is largely decoupled from the overlayer crystallinity, and ͑c͒ the concentration of implanted H + ions decreases at higher implantation energies at the interface, thus decreasing the degree of implantation damage at the interface proper.

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