ULTRASONIC STUDIES OF ELASTIC, ELECTROMECHANICAL, AND ELECTRICAL BEHAVIOR IN CADMIUM(,1-X)MANGANESE(,X)TELLURIUM WITH 0 LESS THAN OR EQUAL TO X LESS THAN OR EQUAL TO 0.52 AND IN CADMIUM(,0.52)ZINC(,0.48)TELLURIUM
Abstract
The elastic constants of single crystals of Cd(,1-x)Mn(,x)Te with 0 (LESSTHEQ) x (LESSTHEQ) 0.52 and a single crystal of Cd(,0.52)Zn(,0.48)Te at 296 K are determined at 296 K using hydrostatic pressures up to 4 kbar from measurements of the transit times of 30 MHz ultrasonic waves. It is found that Mn, but not Zn, weakens the zinc blende crystal structure and makes it less stable under pressure. Applying a modified Born criterion to our data we deduce the pressure expected to cause the transition to the rock salt structure in each compound. The influence of Mn we attribute to Mn 3d orbitals hybridizing into the tetrahedral bonds. The attenuation and velocity of piezoelectrically active ultrasonic shear waves in Cd(,0.48)Mn(,0.52)Te and Cd(,0.55)Mn(,0.45)Te and the velocity of such waves in CdTe and Cd(,0.52)Zn(,0.48)Te are determined as a function of temperature. We find an attenuation maximum and/or velocity change associated with a thermally-activated electrical conductivity which indicates that electromechanical coupling and the piezoelectric constant are much larger in our Cd(,1-x)Mn(,x)Te samples than in CdTe or Cd(,0.52)Zn(,0.48)Te. This is due mainly to a smaller strain-induced shift of bonding charge in Cd(,1-x)Mn(,x)Te which we suggest is caused by hybridization of Mn 3d states into the tetrahedral bonding orbitals. From the electrical conductivity determined by fitting calculated curves to our ultrasonic data we deduce the ionization energies for the centers which provide the mobile charge carriers (holes) responsible for the electrical conductivity. The energies are similar to those found for various centers identified by others in as-grown or doped Cd(,1-x)Mn(,x)Te and in as-grown ZnTe.
Degree
Ph.D.
Subject Area
Condensation
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