PDMS-based photonic and quasi-photonic crystal for LED application

The photonic crystals (PhCs) and photonic quasi-crystals (PQCs) have the considerable effect on enhancement of extraction efficiency and radiation pattern of light emitting diodes (LEDs). We present thin polymer membranes based on polydimethylsiloxane (PDMS) with PhC and PQC patterned surface for direct application on the LED chip. The patterned PDMS surface was achieved by embossing of liquid PDMS (Sylgard 184) on structured photoresist surface prepared by interference lithography. The patterned PhC and PQC modify the Lambertian radiation diagram of conventional LEDs. Radiation properties of LEDs were documented from far-field emission by goniophotometer measurements. Structure quality and symmetry was examined by atomic force microscope and related to the measured diffraction pattern of the PhC and PQC LEDs. The emitting LEDs were also investigated in the near field using the near-field scanning optical microscope. Presented results favor patterned PDMS membranes for the employment in LED emission improvement and with considerable effect on light diffraction.