The recombination of excess electron-hole pairs in indium antimonide has been studied in the temperature range 200°K-15°K, where it is controlled by localized centers. Minority carrier trapping is found in extrinsic ^-type material. The lifetimes of electrons and holes obtained from photoconductivity and photoelectromagnetic effect data on n-and i>-type samples lead to a model for the recombination, consisting of a donor center having two energy levels in the forbidden gap, at 0.055 and 0.12 ev above the valence band. The capture coefficients for holes and electrons have been determined for the center in each of the two charge states. In />-type material, the chemical acceptors are in statistical equilibrium with the free holes in the valence band. When holes freeze out onto acceptor centers (r<60°K), an increase of free holes due to photoexcitation leads to a corresponding increase in the hole concentration on the acceptors. This effect of majority carrier trapping reduces the rise of hole lifetime with decreasing hole concentration. In order to determine the nature of the recombination centers, different treatments are used to introduce additional centers. It is found that bombardment with 4.5-Mev electrons produces additional centers having the same recombination properties as the original centers. The result indicates that the recombination centers have the nature of structural defects rather than chemical impurities.
A laser beam, incident on a highly absorbent thin film supported by a poorly conductive substrate, causes that film to heat and melt. The time required to reach the melting point and that required to complete the melting process are calculated as a function of the incident laser flux. The calculations neglect heat losses arising from lateral diffusion, convection, and thermal radiation, but they account for a possible reflectivity change at the melting point. They yield a criterion for the minimal absorbed flux necessary to maintain stable monotonic melting.
A monolithic array of AlGaAs lasers has been packaged together with an array of fiber lightguides on a substrate of silicon. The components have been optimized for maximum lightguide output radiance consistent with reliable cw laser operation. Coupling efficiencies up to 80% have been achieved between laser and lightguide. Output powers up to 70 mW cw have been observed from a 50-microm core diameter lightguide of 0.15 numerical aperture. Eight-device array multispot packages have been fabricated with 10 mW/spot, limited by laser quality and thermoelectric cooler capacity. Fabrication tolerances and device electrical and optical crosstalk are discussed.
Magnetoresistance was studied for w-type single-crystal germanium of 4X10 15 effective donors/cm 3 . The effective anisotropy parameter K was found to decrease from ^20 at 300°K to ^6 at 20 °K. Values close to 20 were again obtained at 7°K and 4.2°K. By introduction of compensating acceptors with heat treatment, it was shown directly that the decrease of K was due to anisotropic scattering by ionized impurities, and the anisotropy was investigated by using different degrees of compensation. Below 7°K, the scattering is determined by neutral impurities, and the high value of K indicates that the scattering is isotropic.
Thermal resistance and crosstalk have been investigated for a source package consisting of a monolithic, multilaser heterojunction array mounted on a single crystalline silicon substrate, which is in turn laminated to a copper heatsink. Models for 2-D and 3-D heat spreading are used to calculate the heat flow distribution and to obtain upper and lower bounds for both resistance of single devices and crosstalk in arrays. Results for experimental five-laser arrays are shown to fall within these limits. Active cooling is required to maintain junctions at safe operating temperatures prerequisite to stable, long-lived operation.
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