Deep-ultraviolet photonic crystal surface-emitting lasers

We have demonstrated the first optically pumped UVC PCSELs and now developed deeply etched photonic crystals for future electrically driven devices. To better understand these PCSELs we have investigated how sensitive the thresholds and far-fields are to a variation in lattice constant and lateral PCSEL size by both angular-resolved photoluminescence measurements and 3D coupled-wave theory simulations. As expected, the threshold pump power density decreases with increasing PCSEL size due to an increased lateral loss. In addition, smaller PCSELs (Ø ≤ 68.5µm) show narrow doughnut-shaped far fields, while larger PCSELs lase in multiple modes on the photonic crystal dispersion, yielding a degraded far-field. A similar transition is observed when varying the lattice constant for a fixed PCSEL diameter. There is thus a trade-off between low threshold and narrow far-fields where both PCSEL size and lattice constant affect final characteristics. Additional challenges towards electrically driven UV PCSELs will also be discussed.