Polarization field and electronic states of GaN pyramidal quantum dots in AIN

Atomistic calculations for the electronic states of GaN quantum dots (QDs) in AlN have been carried out using the polarization -potential-dependent sp(3) tight-binding method. In this calculation, a valence-force-field method is used for the strain distribution, and a finite-difference-method for the polarization-induced potential and field. The dot shape examined is a truncated hexagonal pyramid with the bottom diameter of 101.4 Angstrom and height of 20.7 Angstrom, corresponding to the "small QD samples" in the experiment. We find that the built-in electric field (max. 7.14 MV/cm) is induced in the QD due to the piezoelectric and spontaneous polarization. The transition energy between the ground electron and hole levels is 3.653 eV. Under the strong field, the electron state moves up toward the QD top, and the hole state moves down toward the bottom, resulting in the reduction of the squared wave function overlap to 7.97 X 10(-2).