Spin scattering by dislocations in III-V semiconductors

A semiclassical treatment of spin relaxation in direct-gap compound semiconductors due to scattering by edge dislocations from both charged cores, and the strain fields surrounding them is presented. The results indicate a deleterious effect on spin transport in narrow bandgap III-V semiconductors due to dislocation scattering. However, this form of scattering is found to be surprisingly benign for wide-bandgap semiconductors with small spin-orbit coupling (such as GaN). This observation leads to a proposal for possible lattice-mismatched hybrid heterostructure devices that take advantage of the long spin lifetimes of the wide-bandgap semiconductors for transporting spin over large distances acting as spin-interconnects, and the wide tunability of spin in the narrow-bandgap semiconductors for spin logic operations.

Figure 1

The strain and Coulomb fields around edge dislocations that cause spin scattering are shown schematically. Without screening by free carriers, the strain field follows a $\sin \phi ∕r$ dependence from the dislocation core, and the Coulomb field follows a $1∕r$ dependence.

Figure 2

Spin-scattering time due to dislocations calculated for the nondegenerate regime. The electron concentration and dislocation density is assumed constant. The room-temperature spin-scattering rate for GaN is in good agreement with the experimentally measured value (Ref. 8). Also note that spin scattering by dislocations is very weak for wide-gap semiconductors with small spin-orbit coupling.

Figure 3

Relative strengths of individual dislocation spin-scattering mechanisms for GaN. Note that for spintronic devices operating near room-temperature, DP scattering from the strain fields surrounding dislocations dominates spin transport.

Figure 4

Spin-scattering times by dislocations for degenerate electron populations for the three semiconductors. Note that in the regime covered, the larger the dislocation density, the less is the spin scattering for the same carrier concentration, highlighting the importance of the DP scattering mechanism. For the same dislocation density, spin-scattering becomes more efficient with increasing carrier density. Temperature does not play a role for the ideal degenerate carrier distribution considered.

Figure 5

Exact ratios ${\Phi }_{\mathrm{st}},{\Phi }_{\mathrm{ch}}$ and ${\gamma }_{\mathrm{st}},{\gamma }_{\mathrm{ch}}$, that relate the spin scattering rates to the momentum scattering rates, and their asymptotic values as a function of the dimensionless quantity $x=k\lambda$. $\Phi$ terms are due to the Elliott-Yafet scattering mechanism, and $\gamma$ terms due to the D’Yakonov-Perel scattering mechanism.