Crystal growth and p-type conductivity control of AlGaN for high-efficiency nitride-based UV emitters

Assessment of AlGaN/AlN superlattices on GaN nanowires as active region of electron-pumped ultraviolet sources

In this paper, we describe the design and characterization of 400 nm long (88 periods) Al _x Ga_1-x N/AlN (0 ≤ x ≤ 0.1) quantum dot superlattices deposited on self-assembled GaN nanowires for application in electron-pumped ultraviolet sources. The optical performance of GaN/AlN superlattices on nanowires is compared with the emission of planar GaN/AlN superlattices with the same periodicity and thickness grown on bulk GaN substrates along the N-polar and metal-polar crystallographic axes. The nanowire samples are less sensitive to nonradiative recombination than planar layers, attaining internal quantum efficiencies (IQE) in excess of 60% at room temperature even under low injection conditions. The IQE remains stable for higher excitation power densities, up to 50 kW cm^-2. We demonstrate that the nanowire superlattice is long enough to collect the electron-hole pairs generated by an electron beam with an acceleration voltage V _A = 5 kV. At such V _A, the light emitted from the nanowire ensemble does not show any sign of quenching under constant electron beam excitation (tested for an excitation power density around 8 kW cm^-2 over the scale of minutes). Varying the dot/barrier thickness ratio and the Al content in the dots, the nanowire peak emission can be tuned in the range from 340 to 258 nm.

Transparent conductive oxide films mixed with gallium oxide nanoparticle/single-walled carbon nanotube layer for deep ultraviolet light-emitting diodes

We propose a transparent conductive oxide electrode scheme of gallium oxide nanoparticle mixed with a single-walled carbon nanotube (Ga2O3 NP/SWNT) layer for deep ultraviolet light-emitting diodes using spin and dipping methods. We investigated the electrical, optical and morphological properties of the Ga2O3 NP/SWNT layers by increasing the thickness of SWNTs via multiple dipping processes. Compared with the undoped Ga2O3 films (current level 9.9 × 10-9 A @ 1 V, transmittance 68% @ 280 nm), the current level flowing in the Ga2O3 NP/SWNT increased by approximately 4 × 105 times and the transmittance improved by 9% after 15 times dip-coating (current level 4 × 10-4 A at 1 V; transmittance 77.0% at 280 nm). These improvements result from both native high transparency of Ga2O3 NPs and high conductivity and effective current spreading of SWNTs.