The band-gap energy Eg of silicon has been reevaluated with high precision between 2 and 300 K by the following method: the derivative of the absorption coefficient, resulting from free-exciton absorption, has a well-defined singularity, which can be detected unambiguously by wavelength-modulation spectroscopy. The energy of this singularity yields the band gap. Our data deviated by more than 5 meV from the earlier results of MacFarlane et al. and Haynes et al. and fell between their Eg(T) curves. The approximation of Eg(T) = A + BT + CT2 gives A = 1.170 eV, B = 1.059×10−5 eV/K, and C = −6.05×10−7 eV/K2, for 0<T≤190 K, and A = 1.1785 eV, B = −9.025×10−5 eV/K, and C = −3.05×10−7 eV/K2, for 150≤T≤300 K, which fits our data within 0.2 meV. The major uncertainty of about 1 meV lies in the energies of exciton and TO phonon.

Photoluminescence measurements with high spatial and spectral resolution on ^-type GaAs at helium temperatures show the reduction of radiative quantum efficiency immediately at individual deformation-induced dislocations to be orders of magnitude stronger than near grown-in dislocations.Dislocations in semiconductors can lead to formation of distinct electronic levels and cause inhomogeneities of charge and dopant distributions. 1 Radiative recombination of electron-hole pairs is known to be affected by the presence of dislocations. 2 *" 4 However, the details of the fundamental processes of recombination at and around dislocations are still insufficiently understood. For GaAs, this question has recently become of exceptional importance because the quantum efficiency of injection lasers is degraded by dislocation effects. 5 " 8 In this paper we present the first definitive correlations between dislocations and recombination by measuring luminescence spectra directly at and adjacent to individual dislocations of various origin. High spatial resolution on the specimen surface is combined with high spectral resolution at helium temperatures for identification of the specific electronic transitions in w-type GaAs.A special helium cryostat 9 enabled us to position the samples as close as 12 mm to an external microscope illuminator system, which is used to focus light from a He-Ne laser onto the sample for photoluminescence excitation and to collect the recombination radiation for analysis in a grating spectrometer. The cryostat was mounted on a micrometer stage with motion feasible in both coordinates within the plane of the sample surface. A spatial definition of better than ± 3 pm was achieved.The excitation intensity was kept low to avoid disturbances. Less than 0.8 mW of the 1.96-eV laser radiation impinged on the sample. We convinced ourselves of the independence of our results upon excitation level by inserting a series of neutral-density filters. Sample temperature during excitation was approximately 10 K.The samples to be discussed here were w-type GaAs, Se-doped, with room-temperature electron concentrations between (3 and 4) xlO 17 cm" 3 . Electron mobility at room temperature was typically 3300 cm 2 V" 1 sec" 1 . We estimate the compensation to be of the order of 20%, mostly due to silicon acceptors. The surfaces, of (100) orientation, could be etched after the luminescence was taken in order to correlate the details of the spectra with dislocation etch-pit distributions or dopant striations. 10

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