Plastic deformation in semiconductors is governed by the motion and interaction of dislocations, which are line defects that enable permanent shape change without catastrophic failure. Unlike metals, semiconductors exhibit covalent or mixed covalent-ionic bonding, leading to high Peierls barriers that restrict dislocation motion. The primary mechanisms include dislocation generation, glide, and multiplication, which are strongly influenced by crystal structure, strain rate, and temperature.

Dislocations in semiconductors are characterized by their Burgers vectors and slip systems. In diamond cubic structures like silicon and germanium, the predominant slip system is {111}⟨110⟩. The {111} planes are the closest-packed, offering the lowest energy for dislocation movement. The ⟨110⟩ Burgers vector represents the shortest perfect lattice translation vector. Zincblende structures, such as GaAs and InP, also exhibit {111}⟨110⟩ slip systems but with additional complexities due to their polar nature, leading to differences in dislocation behavior on the A (group III-terminated) and B (group V-terminated) {111} planes. Wurtzite semiconductors like GaN and ZnO deform primarily on the (0001) basal plane with ⟨1120⟩ Burgers vectors, though prismatic and pyramidal slip systems may activate under certain conditions.

Dislocation generation occurs through heterogeneous nucleation at stress concentrators like surface imperfections, inclusions, or pre-existing defects. Homogeneous nucleation is rare due to the high stresses required to create dislocations in perfect crystals. Under applied stress, dislocations glide on their slip planes, overcoming the Peierls barrier through thermal activation. The velocity of dislocations follows an Arrhenius-type relationship: v = v0 exp(−Q/kT), where v0 is a pre-exponential factor, Q is the activation energy, k is Boltzmann’s constant, and T is temperature. For silicon, the activation energy for dislocation glide ranges from 2.0 to 2.3 eV, depending on the dislocation type (screw or 60° mixed).

Dislocation multiplication is critical for sustained plastic deformation and occurs via mechanisms like the Frank-Read source. A pinned dislocation segment bows out under stress, eventually forming a loop that expands and regenerates the original segment. Cross-slip, where a screw dislocation changes slip planes, also contributes to multiplication, particularly in high-stress conditions. In compound semiconductors, multiplication is complicated by the dissociation of dislocations into partials separated by stacking faults. For example, in GaAs, a perfect 60° dislocation dissociates into 30° and 90° partials with a stacking fault ribbon in between, influencing glide and multiplication dynamics.

Strain rate plays a significant role in plastic deformation. At low strain rates, dislocations have sufficient time to overcome the Peierls barrier via thermal activation, leading to lower flow stresses. High strain rates increase the flow stress as dislocations must move faster, requiring higher applied stresses to compensate for reduced thermal assistance. Experiments on silicon show that increasing the strain rate from 10−5 to 10−3 s−1 can raise the yield stress by 20-30% at room temperature.

Temperature dependence is another critical factor. At low temperatures, dislocation motion is hindered by the high Peierls barrier, resulting in brittle behavior. As temperature increases, thermal energy aids dislocation glide, reducing the flow stress. For instance, silicon’s critical resolved shear stress drops from approximately 1 GPa at 600°C to 10 MPa at 900°C. In III-V compounds, the temperature dependence is more pronounced due to their lower thermal conductivity and higher sensitivity to point defect interactions.

The core structure of dislocations also affects plasticity. In covalent semiconductors, dislocations reconstruct to minimize dangling bonds, creating electrically inactive but mechanically stable cores. For example, in silicon, the 30° partial dislocation reconstructs into a period-doubled structure, while the 90° partial remains unreconstructed. These core configurations influence mobility, with 30° partials gliding more easily than 90° partials. In polar semiconductors like GaN, dislocation cores may acquire charges, leading to electrostatic interactions that further modify glide behavior.

Strain hardening in semiconductors arises from dislocation interactions, such as the formation of junctions or tangles. Unlike metals, where forest hardening dominates, semiconductors exhibit more complex behavior due to the directional nature of their bonding. Dislocation-dislocation reactions can produce sessile locks that impede further motion. For example, in silicon, the reaction between two 60° dislocations can form a stair-rod dislocation, effectively hardening the material.

The influence of doping on plastic deformation is notable. In silicon, n-type doping with phosphorus or arsenic increases dislocation velocity due to electron-mediated reconstruction of dislocation cores. P-type doping with boron decreases velocity, as holes localize on dislocation cores, increasing their effective mass. In compound semiconductors, doping can alter the charge state of dislocations, modifying their mobility and interaction energies.

High-pressure deformation introduces additional complexity. Under hydrostatic pressure, the Peierls barrier increases due to reduced atomic spacing, raising the critical stress for dislocation motion. However, pressure can also activate secondary slip systems that are otherwise energetically unfavorable. For example, in GaN, high pressure promotes non-basal slip, altering the deformation microstructure.

In summary, plastic deformation in semiconductors is a thermally activated process dominated by dislocation glide and multiplication. Slip systems are determined by crystal structure, with diamond cubic, zincblende, and wurtzite materials exhibiting distinct behaviors. Strain rate and temperature significantly influence dislocation dynamics, while doping and pressure provide additional tuning knobs. Understanding these mechanisms is essential for designing semiconductor devices with improved mechanical reliability and performance.