{'fraction_non_alphanumeric': 0.023255813953488372, 'fraction_numerical': 0.0, 'mean_word_length': 5.8, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Two-beam cross-modulation photocarrier radiometry: principles and contrast amplification in semiconductor subsurface imaging

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 IeR, 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.