Optical Spectroscopy of GaN/Al(Ga)N Quantum Dots Grown by Molecular Beam Epitaxy

Abstract: GaN quantum dots grown by molecular beam epitaxy are examined by micro-photoluminescence. The exciton and biexciton emission are identified successfully by power-dependence measurement. With two different samples, it can be deduced that the linewidth of the peaks is narrower in the thicker deposited layer of GaN. The size of the GaN quantum dots is responsible for the binding energy of biexciton (EbXX); EbXX decreases with increasing size of GaN quantum dots. Under polarization studies, polar plot shows that emission is strongly linear polarized. In particular, the orientation of polarization vector is not related to any specific crystallography orientation. The polarization splitting of fine-structure is not able to resolve due to limited resolution of the system. The emission peaks can be detected up to 80 K. The curves of transition energy with respect to temperature are S-shaped. Strain effect and screening of electric field account for  blueshift of transition energy, whereas Varshni equation stands for redshifting. Both blueshifting and redshifting are compensated at temperature ranging from 4 K to 40 K.