Design and fabrication of photonic crystal structures by single pulse laser interference lithography

Photonic crystal (PhC) structures formed by periodic surface nanostructuring have emerged as pivotal elements for controlling light-matter interactions. One important application is reducing losses due to the high surface reflectivity of semiconductor optoelectronic devices, such as enhancing light absorption in photovoltaic cells or improving light extraction in light-emitting diodes (LEDs). Although various methods for fabricating such structures have been documented, the utilization of single pulse laser interference lithography (LIL) using commercial photoresist and its subsequent effective use as an etch mask has not been previously reported. Rapid exposure of photoresists with single nanosecond pulses offers benefits for high throughput patterning and reduces the requirement for a stable optical platform. We have successfully employed single pulse LIL to fabricate antireflective PhC structures on GaAs substrates using a commercial photoresist. Exposure is performed with single 7 ns 355 nm pulses of relatively low energy (<10 mJ). High-quality nanohole arrays of pitch of approximately 365 nm are fabricated and depths up to 400 nm have been etched using inductively coupled plasma (ICP) through the exposed photoresist mask. Reflectivity analyses confirmed that these structures reduce the average reflectance of the GaAs to below 5 % across the 450 nm to 700 nm visible wavelength range. The fabrication of PhC structures using this approach has potential for low-cost wafer-level patterning to provide improved light extraction in LEDs and enhanced light trapping in solar cells.