Methods The layer structure of a simulated deep UV LED is basically similar to that of recently reported

deep UV LEDs [3, 4]. The layer structures are assumed to be grown on a sapphire substrate and consist of a 2-μm-thick n-Al0.6GaN layer, 50-nm-thick Al0.45GaN/Al0.56GaN multiple quantum well (MQW) active layers, a 50-nm-thick p-Al0.6GaN layer, and a p-GaN contact layer. selleck chemical It is assumed that the simulated UV LED chip is not encapsulated and thus exposed to air. In this work, we consider two types of LED structures: planar and nanorod structures. Figure  1 shows the cross section of the FDTD computational domain for simulated LED structures. In the nanorod LED structure, the sidewall of the nanorod is filled with SiO2 layers for passivation. The cross section of the nanorod is assumed to have a hexagonal shape as shown in Figure  1c because nanorod structures are mostly grown in the shape of a hexagon [16]. In the simulations, the dependence of LEE on the height (h) and diameter (d) of the nanorod structure will be investigated. Figure 1 Schematic diagram of FDTD computational domain. Side view of the simulated LED structure is shown for (a) the planar LED and (b) nanorod LED structures. PMLs are employed for the absorption boundary

H 89 purchase condition of the FDTD simulation. The detection plane for extracted light is indicated as dotted red line. (c) Cross-sectional view of the simulated Selleck NSC23766 nanorod LED structure. In the FDTD simulation, a single dipole source is positioned in the middle of the MQW active region. The spectrum of the dipole source has a Gaussian shape. Center wavelength and full width at half maximum of the spectrum are assumed to be 280 and 10 nm, respectively. The dipole source is polarized in the direction either parallel to the MQW plane for the excitation of the TE mode or perpendicular to the MQW plane for the excitation

of the TM mode. In the computational domain shown in Figure  1, the dipole source for the TE and TM modes is set to be polarized Masitinib (AB1010) in the x and z directions, respectively. The propagating light is completely absorbed without reflection in the PML. The Poynting vectors are calculated on the surfaces near PMLs and used to determine LEE of LED structures. LEE is defined as the fraction of emitted power out of the LED structure to the total emitted power, which is determined by the ratio of Poynting vectors integrated over extraction surfaces to total integrated Poynting vectors [18]. The plane for detecting extracted light is shown as dotted red line of the computational domain in Figure  1. In order to obtain reliable simulation results, it is important to properly choose the refractive index and absorption coefficient of each material. The absorption coefficient of the GaN layer is chosen to be 170,000 cm-1[20, 21]. Light is strongly absorbed in the GaN layer due to the large absorption coefficient.