High pressure significantly alters the defect dynamics in semiconductors by modifying atomic bonding, lattice parameters, and thermodynamic equilibria. The behavior of defects—including dislocations, vacancies, interstitials, and impurities—is governed by stress-dependent energetics and kinetics. Studies on silicon (Si) and gallium arsenide (GaAs) under high-pressure conditions reveal distinct trends compared to ambient-pressure scenarios, providing insights into defect engineering for advanced semiconductor applications.
Under high pressure, the lattice contracts, increasing atomic packing density and altering the formation energies of point defects. In silicon, for example, the formation energy of a vacancy rises with pressure due to the increased elastic strain required to remove an atom from the compressed lattice. At pressures exceeding 10 GPa, ab initio calculations show a 20-30% increase in vacancy formation energy compared to ambient conditions. Conversely, interstitial formation energies may decrease under pressure because the compressed lattice provides more favorable sites for additional atoms. This shift in equilibrium leads to a reduction in vacancy concentration and a potential increase in interstitial populations at high pressures.
Dislocation behavior is also pressure-sensitive. In GaAs, high-pressure studies reveal that dislocation mobility is suppressed due to enhanced Peierls barriers under compressive stress. At pressures above 5 GPa, glide velocities of dislocations decrease by an order of magnitude compared to ambient conditions. This suppression is attributed to the increased shear modulus and reduced atomic spacing, which hinder dislocation kink formation and propagation. In contrast, ambient-pressure studies (G1) show that dislocations in GaAs readily multiply and glide under mechanical stress, leading to plastic deformation at much lower stresses.
Point defect migration is similarly affected. In silicon, the activation energy for vacancy diffusion increases under pressure, as the lattice stiffness impedes atomic jumps. Experimental data indicate a 15% increase in migration energy at 8 GPa. Interstitial diffusion, however, may exhibit a non-monotonic pressure dependence. Some studies suggest that at moderate pressures (2-6 GPa), interstitial migration is accelerated due to the availability of lower-energy pathways in the distorted lattice, while at higher pressures, diffusion slows as the lattice becomes too rigid.
High-pressure conditions can also induce defect annihilation mechanisms not observed at ambient pressure. In GaAs, high-pressure annealing experiments demonstrate enhanced recombination of vacancies and interstitials due to the increased chemical potential of defects. At 7 GPa and 800 K, point defect densities drop by nearly 50% within minutes, whereas similar annealing at ambient pressure requires hours to achieve comparable reductions. This accelerated annihilation is linked to the pressure-induced reduction in defect stability and the increased driving force for recombination.
A key contrast with ambient-pressure defect studies (G1) lies in the role of thermodynamic equilibria. At ambient pressure, defect concentrations are primarily governed by temperature and impurity content, with equilibrium established over longer timescales. Under high pressure, the system reaches a quasi-equilibrium state where defect populations are dynamically adjusted according to the instantaneous stress state. For instance, in silicon, high-pressure quenching experiments reveal metastable defect configurations that persist upon pressure release, unlike the rapid relaxation observed in ambient-pressure quenching.
Case studies on Si and GaAs further illustrate these effects. In silicon, high-pressure phase transitions (e.g., from diamond cubic to beta-tin at ~12 GPa) introduce new defect types, such as stacking faults and partial dislocations, which are absent in ambient-pressure samples. Post-transition recovery to the diamond cubic phase often leaves behind residual defects, including microtwins and dislocation loops. In GaAs, high-pressure treatment above 20 GPa induces irreversible defect complexes involving arsenic vacancies and gallium interstitials, which degrade carrier mobility even after pressure release.
The interplay between pressure and extrinsic defects is another critical factor. In doped semiconductors, high pressure can alter the solubility and activation of impurities. For example, in boron-doped silicon, pressures above 5 GPa enhance boron activation by reducing the formation of inactive boron-vacancy pairs. Conversely, in GaAs doped with silicon, high pressure promotes the formation of Si-As complexes, which act as compensating centers and reduce n-type conductivity.
Practical implications of high-pressure defect control include the synthesis of high-quality bulk crystals and the tuning of optoelectronic properties. High-pressure growth of silicon carbide (SiC) at 2-3 GPa suppresses micropipe defects, yielding crystals with lower dislocation densities than those grown at ambient pressure. Similarly, high-pressure annealing of GaN reduces yellow luminescence by eliminating nitrogen vacancies and related deep-level traps.
In summary, high pressure profoundly influences defect formation, migration, and annihilation in semiconductors through modifications in lattice energetics and kinetics. The contrasting behaviors observed under high pressure versus ambient conditions (G1) highlight the importance of stress as a tool for defect engineering. Case studies on Si and GaAs demonstrate both challenges and opportunities in leveraging high-pressure effects for advanced material processing. Future research may explore pressure-assisted defect control in emerging semiconductors, such as wide-bandgap oxides and 2D materials, to further optimize their performance in extreme environments.