Growth and characterization of InGaN/GaN nanocolumn LED

Abstract

GaN nanocolumn (sometimes called as nanorod, nanowire, and nanopillar) is a columnar single crystalline GaN nano-crystal having small diameter of from tens to hundreds nanometers. In this paper, photoluminescence (PL) study of GaN nanocolumns and InGaN multiple quantum disks (MQDs) embedded in the GaN nanocolumns grown by RF-plasma assisted molecular beam epitaxy are described. The room temperature PL peak intensity of GaN nanocolumns was several hundred times stronger than that of conventional GaN film with dislocation density of 3~5x10⁹ cm^-2. Stimulated emission with very low threshold optical power density of 198~290 kW/cm² was observed for the GaN nanocolumns. InGaN MQDs also showed intense PL emission with peak wavelength of from 436 (blue) to 614 nm (red). GaN nanocolumn based light emitting diodes (LEDs) with InGaN MQD active layer were successfully fabricated on n-type (111) Si substrates. The emission color of the nanocolumn LED was varied from violet to red by changing the growth conditions of InGaN MQD active layer. The full width at half maximum (FWHM) of emission spectrum of the LED emitting around 500 nm taken from whole semi-transparent top electrode area (Φ=500 μm) was 73.5 nm but from small area (Φ=3 μm) was 37.0 nm. This result suggests that emission spectrum of a single InGaN quantum disk have narrower FWHM but large area LED that contains huge number of nanocolumn LEDs have wider FWHM.