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Details of the structure in the indirect optical-absorption edge of silicon were studied by measuring the dependence of the photocurrent in p−n junctions on the energy of the incident photons. The measurements were made at room and higher temperatures for photon energies 0.75<<1.08 eV. The sensitivity of the method enabled high-resolution measurements in the absorption tail. At room temperature, thresholds were found at ∼0.91, 0.99, and 1.026 eV. The derivative of the response showed extensive fine structure in this tail. The TO- and LO-phonon-assisted transitions to the ground and excited state of the exciton, previously reported in the phonon emission region, were seen here with phonon absorption occurring around 1.054 and 1.065 eV. There was additional structure of unknown origin in this region.

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©1973 American Physical Society