Piezoelectric constant and conductivity relaxation in n-type InP from ultrasonic attenuation measurements

Measurements have been made of the attenuation of 30, 90 and 150 MHz {111}; longitudinal ultrasonic waves and of the d.c. resistivity in chromium-doped, n-type InP from -50 to +150°C. From the attenuation maximum observed for 30 MHz waves we find γe₁₄γ = 0.040 C/m².     

Pressure dependence of the electrical resistivity and the ionization energy of Cr In n-type InP

The electrical resistance of chromium-doped, n-type InP has been found to increase exponentially with hydrostatic pressure (up to 4.7 kbar) at 273 K, 301 K, and 344 K. The resistivity activation energy increases by 6.5 × 10^-6 eV/bar. This rate equals the difference between the pressure dependences of the lowest conduction band minimum at $\text{k}$ = (000) and the <111> subsidiary minima determined by others. Our results indicate that pressure increases the ionization energy of a Cr donor level whose wave function has a large contribution from the <111> minima. It is suggested the Cr donor level is due to Cr⁺³ occupying an indium site.     

Thermal expansivity in semiconducting NbO2

Measurements have been made of sample lengths L_a and L_c parallel to the a- and c-crystallographic directions, respectively, in semiconducting, distorted-rutile (C⁶_4h) structure NbO₂ between 133 K and 360 K using a fused silica LVDT dilatometer system. L_a changes very slightly and goes through a minimum as a function of temperature, T, while L_c increases monotonically with T in a normal manner. This behavior is compared with that of rutile-structure compounds. The present data do not cause significant changes in the elastic stiffness moduli which were deduced previously from ultrasonic transit times using lengths extra-polated from lattice parameter data above room T. Thus the discrepancy between the elastic and calorimetric Debye temperatures reported in the literature remains. Thermal expansion coefficients and Grüneisen anharmonicity parameters are deduced. The expansion coefficients are analyzed into a quasicubic component and a term depending on the anisotropy of the Grüneisen function.