Effect of spontaneous polarization field on diffusion thermopower in AlGaN/GaN heterostructures

Abstract

Polarization field on diffusion thermopower Sd, of a two-dimensional electron gas (2DEG) formed at a wurtzite AlGaN/GaN heterojunction is investigated. The investigations of macroscopic polarization effect on diffusion thermopower over the wide range of temperature and barrier fluctuations bring out the role of spontaneous and piezoelectric polarization fields present in the heterostructure. The induced 2DEG charge density formed at the interface of AlGaN/GaN heterojunction due to in-built spontaneous and piezoelectric fields are assumed to be scattered by acoustic phonons via deformation and piezoelectric couplings, background and remote impurities via Coulomb interaction, interface roughness and interface charges. We find, the dominant contribution is from interface roughness scattering mechanism and that from acoustic phonons via deformation potential is negligible. Theoretical investigations of Sd show that, the effect of the spontaneous polarization is to reduce the diffusion thermopower significantly at practically relevant temperatures.

Keywords

• Diffusion thermopower
• Seebeck coefficient
• Scattering mechanisms
• Spontaneous polarization