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The diffusion coefficients D of helium in silicon, germanium, and diamond were determined from the rate of evolution of helium upon heating boron-doped crystals after slow neutron irradiation:He in C:  DHeC=7.0×10−4exp (−23.4±4.9 kcal/RT),  1510∘<T<2470∘K;He in Si:  DHeSi=5.1×10−4exp (−13.4±1.8 kcal/RT),  740∘<T<1250∘K;He in Ge:  DHeGe=1.8×10−3exp (−14.0±1.8 kcal/RT),  800∘<T<1130∘K.The 90% confidence level for the activation energies is indicated. Experiments in which helium was introduced into silicon by ion bombardment from a discharge plasma gave values of D concordant with the above. The activation energies were calculated theoretically from the differences in interaction energies of the helium in the interstitial site and at the saddle point between two such sites. An exp-6 potential was used with parameters estimated from inert-gas interactions. The theoretical E values were C: 24.8, Si: 6.7, and Ge: 6.4 kcal. The pre-exponential factors D0 as calculated from the vibration frequencies of the interstitial helium were about 10 times higher than the observed.

Zinc‐and cadmium‐doped gallium phosphide crystals have been grown by an open tube halogen transport process at 805°–875°C. The zinc‐doping varied from 1017 to 1019 cm−3 while cadmium could be incorporated at levels ranging from 1016 to 1018 cm−3. We observed a linear dependence of zinc and cadmium concentration on the partial pressure of the dopant in the growth ambient. This linear dependence is evidence for a nonequilibrium, kinetically controlled process. The structural and electrical properties are compared with the properties of crystals grown by the wet hydrogen process. A study of the gallium consumption as a function of experimental variables yielded a Ga to PCl3 ratio of 2.5±0.2 , independent of PCl3 feed rate and carrier gas flow. A ratio of 2.64 is predicted from thermodynamic data provided the species GaCl2false(normalgfalse) can be neglected in the initial reaction between normalHCl and Ga.