Effect of Bi2Te3 and Bi2Se3 nanoparticle coatings for thermoelectric enhancement of GaN epitaxial layer

Gallium nitride (GaN) is a promising wide-bandgap platform for high-temperature thermoelectric applications, yet its inherently low thermopower and high thermal conductivity constrain device efficiency. Here, we enhance the thermoelectric performance of GaN thin films via surface modification with Bi 2 Te 3 and Bi 2 Se 3 nanoparticles deposited on GaN/Al 2 O 3 substrates. X-ray diffraction and transmission electron microscopy confirm the pure-phase formation of the bismuth chalcogenides, while scanning electron microscopy and atomic force microscopy reveal uniform nanoparticle distribution and intimate interfacial contact on GaN. Notably, Bi 2 Se 3 -coated GaN exhibits an anomalously high Seebeck coefficient (∼392 μV/K) despite a high carrier concentration, yielding a peak power factor of ∼ 5.55 mW/m·K 2 approximately ∼ 4.1 × higher than n-GaN. Bi 2 Te 3 coatings further boost carrier mobility and electrical conductivity (up to ∼ 426 S/cm), underscoring the effectiveness of surface nanoparticle layers in decoupling the conventional trade-off between thermopower and conductivity. The enhancements are attributed to favorable modifications of the electronic structure at the interface, such as increased density of states or band convergence, and the differences in electrical conductivity can be associated with the distinct surface chemistry and interparticle interactions of Bi 2 Se 3 and Bi 2 Te 3 . This composite strategy leverages the mechanical and thermal robustness of GaN with the high thermoelectric response of nanostructured chalcogenides and is extendable to other semiconductor platforms. The results chart a viable pathway toward high-temperature thermoelectric devices based on robust semiconductor thin films augmented by high-ZT nanoparticle coatings.