First-principle Calculation And Study Of The Thermoelectric Properties Of GaN-based Semiconductor Materials

Thermoelectric materials are new functional materials which can directly convert thermal energy into electrical energy,or vice versa.GaN-based semiconductor materials have very broad applications in thermoelectric materials due to the characteristics of large band gap,high thermal conductivity,high Seebeck coefficient and temperature resistance.The properties of TE materials are usually characterized by the dimensionless figure of merit ZT.Good TE materials require large power factor S2? and low thermal conductivity ?.The electronic properties of GaN are calculated by the first principle calculation method with the basic approximation theory and density functional theory.The semi-classical Boltzmann theory is used to calculate the TE properties of N-type and P-type GaN semiconductors.Seebeck coefficient,electrical conductivity,power factors and ZT curve are obtained from the calculations.The results show that the Seebeck coefficient decrease with the increasing of N-type and P-type semiconductor carrier concentration,and when the carrier concentration is constant,the Seebeck coefficient increase with the increasing of the temperature.The electrical conductivity increase with the increasing of N-type and P-type semiconductor carrier concentration;and when the carrier concentration is constant,the electrical conductivity decrease with the increasing of the temperature.The power factor of N-type and P-type semiconductor increases first and then decreases with the increasing of carrier concentration.The N-type semiconductor power factor achieve maximum value –1750 ?W/mK2 at the temperature of 300 K and the carrier concentration of 1017cm-3.The P-type semiconductor power factor achieve maximum value –3500?W/mK2 at the temperature of 1200 K and the carrier concentration of 1020cm-3.The thermal conductivity is chosen to be a constant(?=5.85×104/T)due to the little change.With the increase of carrier concentration,the N-type and P-type semiconductor ZT value show a trend of increasing first and then decreasing.The N-type semiconductor ZT achieves maximum value 0.0039 at the temperature of 1200 K and the carrier concentration of 1018cm-3.The P-type semiconductor ZT achieves maximum value0.0085 at the temperature of 1200 K and the carrier concentration of 1020cm-3.Above all,P-type GaN materials have better thermoelectric properties then N type GaN materials.