Growth behavior and stress distribution of bulk GaN grown by Na-flux with HVPE GaN seed under near-thermodynamic equilibrium

Abstract

We used Na-flux method to grow Ga-polar GaN (Ga-GaN) and N-polar GaN (N-GaN) on a double-sided epitaxially polished HVPE-GaN seed. The growth behavior and stress distribution of Ga and N-polar GaN grown by Na-flux method was systematically studied for the first time. Under near-thermodynamic equilibrium growth conditions, the growth rate of the N-polar plane is higher than that of the Ga-polar plane, which is related to the high surface energy of the N-polar plane. The lower overall stress level of Ga-GaN/N-GaN bulk single crystals is confirmed by Raman spectroscopy and low-temperature PL. Three-dimensional atom probe tomography (3D-APT) directly proves that C and O impurities are enriched at the atomic level at the growth interface, resulting in the mismatch of the interface lattice, resulting in compressive stress and reduction of free carriers. Under near-thermodynamic equilibrium growth conditions, the dislocation density of GaN bulk single crystals can be further reduced. Ga-GaN and N-GaN dislocation density values were 4 × 105/cm2 and 8 × 105/cm2, respectively. The mechanism of dislocation reduction is discussed. In addition, we can achieve control of stress and free carriers by adjusting the behavior of impurity incorporation.