The effect of low Al concentration on the electronic structure and thermoelectric properties of AlxGa1−xN/GaN heterojunctions

The effect of low Al concentrations on the electronic structure and thermoelectric properties of Al_xGa_1-xN/GaN (x = 0.1250, 0.1875, 0.2500, and 0.3125) heterojunctions was investigated using density functional theory and Boltzmann transport theory. Compared to Al_xGa_1-xN/GaN heterojunctions with different Al concentrations, it was found that: (1) The bandgap increases and the density of states (DOS) decreases near the Fermi level as the Al concentration increases in Al_xGa_1-xN/GaN heterojunctions. (2) The Seebeck coefficient of the Al_0.25Ga_0.75N/GaN heterojunction reaches 1850.20 μV/K at 300 K. (3) For n-type samples, the increase of Al concentration leads to higher conductivity in Al_xGa_1-xN/GaN heterojunctions. (4) Power factor (PF) decreases with increasing Al concentration in Al_xGa_1-xN/GaN heterojunctions. At the lowest Al concentration, the power factor of the Al_0.125Ga_0.875N/GaN heterojunction reaches 1.48 × 10¹¹W/(m·K²·s) at 900K. (5) The maximum electronic thermoelectric quality factor (ZT_e) of the Al_0.25Ga_0.75N/GaN heterojunction reaches 1.41, and at the same temperature, the n-type Al_xGa_1-xN/GaN heterojunctions exhibit significantly higher performance than the p-type. The results are useful for exploring the thermoelectric properties of GaN-based heterojunctions and improving the performance of thermoelectric devices.