Holistic nanowire laser characterization as a route to optimal design

Abstract

Nanowire lasers are sought for near-field and on-chip photonic applications as they provide integrable, coherent and monochromatic radiation. A wavelength-scale nanowire acts as both the gain medium and the cavity for the lasing action: the functional performance (threshold and wavelength) is therefore dependent on both the opto-electronic and crystallographic properties of each nanowire. However, scalable bottom-up manufacturing techniques often suffer from inter-nanowire variation, leading to, often dramatic, differences in yield and performance between individual nanowires. Establishing the relationship between manufacturing controls, geometric and material properties and the lasing performance is a crucial step towards optimisation, however, this is challenging to achieve experimentally due to the complex interdependance of such properties. Here, we present a high-throughput correlative approach to characterise over 5000 individual GaAsP/GaAs multiple quantum well nanowire lasers. Fitting the spontaneous emission provides the threshold carrier density, while coherence length measurements measures end-facet reflectivity. We show that the lasing wavelength and threshold are intrinsically related to the width of a single quantum well due to quantum confinement and bandfilling effects. Unexpectedly, there is no strong relationship between the properties of the lasing cavity (facet reflectivity and distributed losses) and the threshold: instead the threshold is negatively correlated with the non-radiative recombination lifetime of the carriers. This approach therefore provides an optimisation strategy that is not accessible through small-scale studies. The quality and width of the quantum wells limit the threshold of these nanowire lasers, rather than the cavity quality.