Temperature Dependence of Spectral Emission from GaN Defect Quantum Emitters*

The study of quantum emitters in technologically mature wide bandgap semiconductors is attractive for photonic integration. We report results on single-photon defect emitters in MOVPE and MBE grown GaN epitaxial layers. Our experimental results show brightness levels for GaN emitters, with integrated solid immersion lenses, comparable to h-BN quantum emitters. GaN emitters display a strong zero phonon line (ZPL) even at room temperature. Interestingly, the temperature dependence of the emission linewidth does not follow a power law, as in the case of most defect emitters (SiC, NV diamond, etc), but exhibits an exponential temperature dependence from 50K to 300K, with a Lorentzian lineshape. The exponential temperature dependence and the corresponding Lorentzian lineshape can be described very well with our model that involves quadratic coupling of the emitter to optical phonons. Below 30K, the emission lineshape is Gaussian and the linewidth saturates at ~0.2 nm. The low temperature linewidth is dominated by spectral diffusion related to the built-in polarization fields in GaN. We will discuss the nature of the GaN defect emitters and the opportunities offered by defect quantum emitters in an optically active wide bandgap material system.