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Samples of n-type PbTe crystals with different electron concentrations (n=2×1017∼5×1019/cc) were prepared by impurity doping or by heating in the vapor of lead. The electrical properties of these crystals were independent of the kind of impurities and depended only on the electron concentration. The electron mobilities of our samples were proportional to n−⅓ at 77°K, and to n−4/3 at 4.2°K. As the conduction electrons in our samples are degenerate at these temperatures, the experimental results mentioned above suggests that the conduction electrons in PbTe crystals are scattered mainly by acoustical mode at 77°K and by neutral imperfections at 4.2°K. Since the electron mobility in PbTe becomes very large at 4.2°K (e.g., 1∼4×106 cm2/v-sec), this material is quite suitable for the experimental studies of the quantum transport phenomena. To investigate such phenomena, the Hall and magnetoresistive effects of n-type PbTe crystals were measured at 4.2°K in a pulsed magnetic field up to 170 kgauss. In the specimens with relatively low electron concentrations (e.g., n≃3×1017/cc), the magnetoresistive effect had a single minimum at about 77 kgauss in a transverse magnetic field, and at about 55 kgauss in a longitudinal field. This minimum should correspond to the situation where the Landau level with l = 1 coincides with the Fermi level in the PbTe crystals.

Reliability of Ti–Pt–Au and Ti–Mo–Au systems has been investigated for GaAs integrated circuit first-level metallizations on semi-insulating GaAs substrates and second-level metallizations on interlayer SiO2 films using Auger depth profile analysis, residual resistance examination and temperature storage step-stress testing. Auger analysis and residual resistance examination showed significant reaction between first-level Ti–Pt–Au and GaAs substrates during metallization processes, while Ti–Mo–Au system with the electron-beam evaporated Mo film showed higher thermal stability because the Mo film acted as a good diffusion barrier between GaAs and Au. The second-level Ti–Pt–Au on SiO2 was found to be free from the reaction with GaAs substrates, and its degradation was ascribed to interdiffusion of composite metals. The resistance increase in step-stress testing for the second Ti–Pt–Au was analyzed on the basis of a new diffusion-controlled model, and long-term reliability was estimated. A mean time to failure value of 3×105 h at 150 °C was obtained for a failure defined as 10% increase in resistance. Much higher reliability was estimated for Ti–Mo–Au, because the resistance continued to decrease as long as 3000 h at 250 °C. The decrease in resistance clearly indicates defect annealing with reduced defect scattering in Au layers. This also shows that foreign metal diffusion into Au, acting as impurity scattering centers, is perfectly eliminated by Mo diffusion barriers.

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High field current-voltage characteristics of n-type GaAs were investigated in the temperature range of 200∼300°K with long samples, and below room temperature remarkable current saturation is found before the current oscillation begins. The critical field for current saturation was nearly the same as that for the Gunn effect at room temperature. The field distribution was observed with a traveling probe, and the formation of stationary high field domain was detected in the current saturation region. A mechanism is proposed to explain the trapping of the high field domain which results in the current saturation and hysteresis effect observed in this experiment.