Non-radiative recombination centres in InGaN/GaN nanowires revealed by statistical analysis of cathodoluminescence intensity maps and electron microscopy.

The methodology of statistical analysis of cathodoluminescence (CL) intensity mappings on ensembles of several hundreds of InGaN/GaN nanowires (NWs) used to quantify non-radiative recombination centres (NRCs) was validated on InGaN/GaN NWs exhibiting spatially homogeneous cathodoluminescence at the scale of single NWs. Cathodoluminescence intensity variations obeying Poisson's statistics were assigned to the presence of randomly incorporated point defects acting as NRCs. Additionally, another type of NRCs, namely extended defects leading to spatially inhomogeneous cathodoluminescence intensity at the scale of single InGaN/GaN NWs are revealed by high resolution scanning transmission electron microscopy, geometrical phase analysis and two-beam diffraction conditions techniques.

Inhomogeneous spatial distribution of non radiative recombination centers in GaN/InGaN nanowire heterostructures studied by cathodoluminescence.

In order to elucidate the mechanisms responsible for cathodoluminescence intensity variations at the scale of single InGaN/GaN nanowire heterostructures, a methodology is proposed based on a statistical analysis on ensembles of several hundreds of nanowires exhibiting a diameter of 180, 240 and 280 nm. For 180 nm diameter, we find that intensitiy variations are consistent with incorporation of point defects obeying Poisson's statistics. For wider diameters, intensity variations at the scale of single NWs are observed and assigned to local growth conditions fluctuations.

Lasing and optical gain around 500 nm from optically pumped lasers grown on c-plane GaN substrates.

Using the variable stripe length method we demonstrated positive net optical gain around 500 nm for an optically pumped laser with InGaN/GaN multiple quantum wells grown on c-plane freestanding GaN substrates. We found that owing to low optical gain, reducing optical losses is crucial to increasing lasing wavelength. We demonstrated lasing at 502 nm by using a 3-mm-long cavity with cleaved facets.