Effect of Pitch and Nanowire Diameter on the Lasing Threshold in InP Photonic Crystal Arrays

Electrically pumped 2D photonic crystal (PhC) lasers have the potential to fulfill the size demands for on-chip coherentlight sources in photonic integrated circuits. In this study, we investigate the effect of the PhC lattice constant (pitch) and the nanowire (NW) diameter on the lasing threshold of optically pumped PhC InP NW arrays at 77 K. The arrays were grown by selective area epitaxy on an InP substrate. The nanowires have mirror-like crystal facets enabling lasing at threshold fluences of less than 10 μJ/cm². NW arrays with pitches of 500, 570 and 630 nm and with NW apothems ranging from 76 to 93 nm have been investigated. The lowest lasing thresholds were obtained in arrays in which the apothem/pitch combination led to a slow Bloch mode (SBM) nearly resonant to or on the low energy side of the InP band emission. PhC samples with off-resonant higher SBM energy show increased threshold values. The observed behavior can be explained by considering both the carrier relaxation and the carrier lifetime in the gain material. InP nanowire arrays with optimized pitch and diameter for low threshold operation are an important step towards electrically pumped PhC lasers.