We report a simple and inexpensive method to enhance the light output efficiency of a GaN-based light-emitting diode (LED). The method employs polydimethylsiloxane (PDMS) films prepared by nanoimprinting on the surface. Two kinds of PDMS films were prepared: one without a pattern and the other with a triangular pattern. After covering with a PDMS film, the light output was increased by about 25% for the LED with a no-pattern film, and about 33% for that with a triangular pattern film. These results can be explained by the surface roughening between the PDMS/air interfaces, which give more opportunity for photons generated in the LED active layer to escape. The research suggests that it is applicable to prepare patterned films by a nanoimprint technique to improve the light output of a GaN-based LED.

We demonstrate low-density quantum dot molecules (QDMs) by selective etching using In droplets as a mask. Selective etching is performed with InGaAs QDMs buried underneath GaAs capping layer, on which In droplets are formed by droplet epitaxy using molecular beam epitaxy. During the chemical etching, the droplets act as a mask and QDMs underneath the droplets that only survive. Photoluminescence measurement from the selectively etched QDMs in mesa structures shows a much reduced intensity, which indicates low-density QDMs. This technique provides a simple and flexible method to attain low-density QDMs. The density can be easily modified by the control of the size and density of In droplets, which is suitable for single QDM spectroscopy and for their device applications.Index Terms-Atomic force microscopy (AFM), droplets, low density, molecular beam epitaxy (MBE), photoluminescence (PL), quantum dot molecules (QDMs), selective etching.