Semiconductors operating in extreme environments, such as high-pressure conditions, exhibit unique mechanical behaviors that directly influence their structural integrity and device reliability. Silicon carbide (SiC) and gallium nitride (GaN) are two prominent materials in this category, valued for their wide bandgap, high thermal conductivity, and robust mechanical properties. Understanding their pressure-dependent mechanical responses—elastic moduli, hardness, and fracture toughness—is critical for applications in aerospace, deep-earth exploration, and high-power electronics where mechanical stability under stress is paramount.

The elastic moduli of semiconductors, including bulk modulus, shear modulus, and Young’s modulus, are fundamental indicators of their resistance to deformation under pressure. For SiC, high-pressure X-ray diffraction and Brillouin scattering studies reveal a bulk modulus ranging between 220-250 GPa at ambient conditions, with a pressure derivative (dK/dP) of approximately 4.0. Under hydrostatic pressures up to 50 GPa, SiC maintains its cubic (3C) or hexagonal (4H/6H) polytype structure, but the elastic constants exhibit nonlinear increases due to bond compression. GaN, with a wurtzite structure, shows a bulk modulus around 210 GPa and a pressure derivative near 4.2. Under pressures exceeding 40 GPa, GaN undergoes a phase transition to a rocksalt structure, accompanied by a marked reduction in elastic stiffness. These transitions are reversible but introduce microstructural defects that can compromise device longevity.

Hardness, a measure of resistance to plastic deformation, is equally pressure-sensitive. Nanoindentation studies under varying pressure conditions demonstrate that SiC’s Vickers hardness increases from approximately 25 GPa at ambient pressure to over 35 GPa at 20 GPa applied pressure. This enhancement is attributed to the suppression of dislocation glide and the activation of alternative slip systems under stress. GaN exhibits a similar trend, with hardness rising from 12 GPa to 18 GPa under comparable pressures. However, the onset of phase transitions in GaN at higher pressures leads to abrupt hardness drops, signaling diminished mechanical stability. These findings underscore the importance of selecting appropriate polytypes and crystal orientations for high-pressure applications.

Fracture toughness, which quantifies a material’s resistance to crack propagation, is another critical parameter. For SiC, pressure-induced lattice stiffening improves fracture toughness marginally, from 3.5 MPa·m¹/² to 4.2 MPa·m¹/² at 15 GPa, due to increased bond covalency and reduced crack tip plasticity. In contrast, GaN’s fracture toughness decreases beyond 30 GPa as phase transitions introduce brittle interfaces and microcracks. Such behaviors highlight the trade-offs between hardness and toughness in these materials under extreme conditions.

Structural changes under pressure are closely linked to these mechanical properties. In SiC, high-resolution TEM studies confirm that pressure-induced stacking faults and partial dislocations dominate deformation mechanisms below the phase transition threshold. For GaN, Raman spectroscopy and synchrotron X-ray data reveal that the wurtzite-to-rocksalt transition initiates at grain boundaries, generating residual stresses that degrade device performance. These structural alterations are particularly detrimental in high-electron-mobility transistors (HEMTs) and Schottky diodes, where interfacial defects increase leakage currents and reduce breakdown voltages.

Device reliability in extreme environments depends on mitigating these pressure-induced degradations. For SiC-based power electronics operating in deep-well drilling equipment, the material’s retained elastic stability up to 50 GPa ensures minimal performance drift. However, GaN devices in aerospace applications require protective coatings or strain-engineered heterostructures to delay phase transitions and maintain operational integrity. Finite element simulations of pressure-loaded semiconductor components further validate that stress concentrations at device edges accelerate failure, necessitating robust packaging designs.

In summary, the pressure-dependent mechanical properties of SiC and GaN are governed by complex interactions between elastic response, plastic deformation, and phase stability. While SiC demonstrates superior resilience across a broad pressure range, GaN’s susceptibility to structural transitions demands careful engineering for high-pressure applications. Advances in in-situ characterization techniques and computational modeling will further refine the understanding of these materials, enabling next-generation devices for extreme environments.