High-temperature mechanical properties of semiconductors are critical for applications in power electronics, aerospace, and other demanding environments where thermal stability and reliability are paramount. Silicon carbide (SiC) and gallium nitride (GaN) are two leading materials in this domain due to their exceptional thermal and mechanical performance under extreme conditions. This article examines key high-temperature mechanical behaviors, including creep, yield strength degradation, and diffusion-assisted processes, with a focus on these advanced semiconductors.

At elevated temperatures, semiconductors experience time-dependent deformation through creep, a phenomenon where materials slowly deform under constant stress. In SiC, creep resistance is notably high due to its strong covalent bonding and low diffusivity. Studies indicate that SiC exhibits minimal creep deformation below 1600°C, with primary creep dominating at lower stresses and secondary creep becoming significant at higher temperatures. The steady-state creep rate of SiC follows a power-law relationship with applied stress, with stress exponents typically ranging between 3 and 5, depending on polytype and impurity content. For instance, 4H-SiC demonstrates superior creep resistance compared to 6H-SiC due to its higher stacking fault energy, which impedes dislocation glide and climb.

GaN, while possessing excellent high-temperature electronic properties, shows more pronounced creep at temperatures above 800°C due to its lower melting point compared to SiC. Dislocation motion in GaN is facilitated by thermally activated processes, leading to increased strain rates under sustained loading. The presence of threading dislocations, common in heteroepitaxial GaN layers, further accelerates creep by providing pathways for dislocation multiplication and glide. However, bulk GaN grown by ammonothermal methods exhibits improved creep resistance, approaching that of SiC at intermediate temperatures (1000–1200°C).

Yield strength degradation is another critical concern for semiconductors operating at high temperatures. The yield strength of SiC remains robust up to approximately 1400°C, beyond which dislocation-mediated plasticity becomes significant. Experimental data show that the yield strength of single-crystal 4H-SiC decreases from around 5 GPa at room temperature to approximately 1 GPa at 1600°C. This reduction is attributed to the increased mobility of dislocations and the activation of additional slip systems at elevated temperatures. In polycrystalline SiC, grain boundary sliding contributes to yield strength degradation, particularly in fine-grained materials where grain boundaries act as sinks for dislocation activity.

GaN exhibits a more rapid decline in yield strength with increasing temperature due to its lower Peierls stress and higher dislocation mobility. At 800°C, the yield strength of GaN drops to roughly half its room-temperature value, with further reductions observed as temperature approaches 1000°C. The wurtzite structure of GaN allows for basal slip as the primary deformation mechanism, with non-basal slip systems becoming active only at very high stresses or temperatures. Doping with elements like iron or magnesium can enhance high-temperature yield strength by pinning dislocations, though this often comes at the cost of reduced electronic performance.

Diffusion-assisted processes play a significant role in high-temperature mechanical behavior, particularly in polycrystalline and composite semiconductor systems. In SiC, carbon diffusion along grain boundaries becomes appreciable above 1500°C, leading to grain boundary migration and coarsening. This can result in time-dependent weakening of the material, especially in sintered SiC ceramics where sintering aids like aluminum or boron accelerate diffusion. Silicon self-diffusion in SiC is extremely slow, with activation energies exceeding 5 eV, which contributes to the material’s stability under prolonged thermal exposure.

GaN suffers from more pronounced diffusion effects, particularly nitrogen vacancy migration, which becomes significant above 900°C. Nitrogen loss at free surfaces or dislocations can lead to the formation of extended defects and voids, degrading mechanical integrity. Additionally, gallium diffusion along threading dislocations can cause localized softening and preferential deformation in heteroepitaxial films. The use of protective coatings, such as aluminum nitride (AlN) capping layers, has been shown to mitigate nitrogen loss and improve high-temperature stability.

The interplay between these mechanical properties determines the reliability of semiconductor devices in high-temperature applications. For SiC-based power electronics, creep and yield strength degradation are manageable up to 1500°C, making it suitable for harsh environments like combustion sensors or nuclear reactor monitoring. GaN devices, while limited to lower operating temperatures (typically below 600°C for commercial electronics), benefit from advanced packaging and thermal management to extend their usable range. In both materials, understanding and controlling diffusion-assisted processes are essential for long-term performance.

Future advancements in high-temperature semiconductor mechanics will likely focus on defect engineering and composite approaches. For SiC, reducing grain boundary activity through optimized sintering techniques or single-crystal growth methods can further enhance creep resistance. In GaN, improving bulk crystal quality and developing stable passivation layers will be key to pushing operational limits. Both materials continue to be at the forefront of high-temperature semiconductor research, driven by their unmatched combination of mechanical and electronic properties.