H. Booyens

Dislocations and the piezoelectric effect in III‐V crystals

It is shown that 60° and 90° α and β dislocations give rise to piezoelectrically induced charge distributions and electric fields in the surrounding crystal. The general features of the charge distributions are discussed with special references to the relation between the nature of the distributions and the symmetry of the crystal. Finally, it is shown that the dislocation reaction (a0/2)[101]+(a0/2)[011]= (a0/2)[110] is self‐consistent as regards electrical properties.

The asymmetric deformation of GaAs single crystals

The deformation of Si‐doped GaAs single crystals with a carrier concentration of 1018 cm−3 was investigated by determining the stress/strain relationships for α and β bending at 500 °C. Marked differences were found between the α and β deformation curves. Using Gilman and Johnston’s model for dislocation multiplication and combining it with a linear relationship between the dislocation velocity and applied stress, a theoretical model was developed to explain the above‐mentioned differences in terms of dislocation mobilities μ, dislocation multiplication factors C, activation stresses τa, and the initial densities of dislocation sources ρ0. Applying a numerical curve fitting procedure to the experimental curves, these parameters were found to have the following values for α and β bending, respectively: μα=8.5×10−12 and μβ=3.8×10−12 cm3 dyn−1 sec−1; Cα=89 and Cβ=130 cm−1; τaα=2.11×108 and τaβ=2.7×108 dyn cm−2; ρ0α=9×105 and ρ0β=4.5×102 cm−2.

Piezoelectric coupling and dislocations in III‐V compounds

By considering the coupling effect between the direct and converse piezoelectric effects, general expressions are derived for the polarization charge distribution and electric field due to a general dislocation with its line along a 〈110〉 direction in undoped crystals of the sphalerite structure. It is found that there exists a line charge on the dislocation which is in general different from the dangling bond charge. Furthermore, there exists a critical value of this charge for which the dislocation attains a minimum energy configuration in which the radial component of the electric field disappears. The equilibrium polarization charge distributions associated with pure edge and 60° dislocations in undoped GaAs are determined numerically. The effects of these charge distributions on the free carriers in crystals are discussed.

The anisotropic carrier mobility due to dislocations in III‐V compounds

The anisotropy in the carrier mobility due to the presence of dislocations in III‐V compounds is determined using a method based on the equivalence of scattering energy loss and Joule heat created in the crystal. It is found that the mobility is a maximum perpendicular to the slip planes of 60° and 90° dislocations of both the α and β types of dislocations. Screw dislocations do not cause any scattering and consequently do not affect the mobility through this mechanism.

The piezoresistance effect and dislocations in III‐V compounds

General expressions for the changes in resistivity and conductivity around 60°, edge, and screw dislocations as a consequence of the piezoresistance effect were calculated for III‐V compounds. These expressions are discussed with reference to the symmetry of the crystal. The specific case of n‐type GaSb is considered and it is shown that 60° and edge dislocations are surrounded by regions of increased and decreased conductivity parallel to the lines of the dislocations. It is also shown that the conductivity parallel to the line of a screw dislocation is increased irrespective of the sign of the Burgers vector. The results indicate that the dislocations can alter the bulk conductivity parallel to their lines and that they can play an important role in the threshold behavior of laser devices. Finally, it is shown that there are charging effects associated with the dislocations during device operation.

On the temperature distributions around dislocations in III‐V compounds due to Joule heating

The nonuniform rate of creation of Joule heat due to variations in the electrical conductivity around dislocations in III‐V compounds gives rise to variations in the temperature around these dislocations. The general equations and boundary conditions for this temperature distribution are derived for any III‐V compound. The specific temperature distributions around 60° and edge dislocations in n‐type GaSb are calculated. It is found that the contribution of the dislocations to the temperature becomes significant within 500 A from the core, while the gradient of temperature reaches significant values at even greater distances.

The thermally enhanced diffusion of point defects near dislocations during device operation

The effect of thermal expansion on the temperature distributions around dislocations in III‐V crystals during conduction parallel to their lines is considered. It is found that the thermal expansion has little effect on the temperature distribution close to the core of the dislocation. It is further shown that these temperature variations give rise to lateral variations in the diffusion constants of point defects and may hence play an important role in device degradation due to the climb of threading dislocations.

Addendum: Dislocations and the piezoelectric effect in III–V crystals

The erroneous assumption that for an insulating crystal the electrical displacement field (?) is zero in the absence of an applied electrical field has led to wrong values for the line charges associated with dislocations as well as for the electric fields and core charges associated with point defects in III‐V crystals. The values for the charge distribution associated with these two types of defects are, however, not affected.