Efficient GaN-based Micro-LED Arrays
- PDF / 199,382 Bytes
- 6 Pages / 595 x 842 pts (A4) Page_size
- 112 Downloads / 197 Views
L6.28.1
Efficient GaN-based Micro-LED Arrays H.W. Choi, C.W. Jeon, M.D. Dawson, P.R. Edwards1 and R.W. Martin1 Institute of Photonics, University of Strathclyde, Glasgow G4 0NW, UK 1 Department of Physics, University of Strathclyde, Glasgow G4 0NG, UK ABSTRACT Highly efficient, two-dimensional arrays of parallel-addressed InGaN blue microLEDs with individual element diameters of 8, 12 and 20µm have been fabricated. In order to overcome the difficulty of interconnecting multiple device elements with sufficient stepheight coverage for contact metallisation, a novel scheme involving the etching of slopedsidewalls has been developed. The devices have I-V characteristics similar to those of broadarea reference LEDs fabricated from the same wafer, and give superior (3mW) light output in the forward direction to the reference LEDs, despite much lower active area. The external efficiencies of the micro-LED arrays improve as the dimensions of the individual elements are scaled down. This is attributed to scattering at the etched sidewalls of in-plane propagating photons into the forward direction. INTRODUCTION As GaN-based light-emitting diode (LED) technology grows in maturity, the focus of many research groups has shifted towards the fabrication of higher power and higher efficiency LEDs. The improvement of output power to date from these devices has been achieved via a number of techniques, including optimisation of epitaxy and processing [1], improved current spreading [2] or through resonant cavity structures [3]. The overall performance of such LEDs is, in addition, strongly dependent on the extraction efficiency of the devices. Due to total internal reflections occurring at the LED-ambient interface, as much as several tens percent of the light emitted from the active region may be confined within the device. In the case of InGaN/GaN LEDs, the novel approaches adopted to allow more light to be extracted include formation by etching of microdisks within the LEDs, to increase the overall surface area [4]. In this manner, apart from benefitting from an enhanced level of light extraction, an enhancement of quantum efficiency was also reported, attributed to micro-size effects as well as to a more efficient usage of the injected current. We investigate here further development of the pattern-etching approach, where arrays of isolated pillar-like micro-size LEDs are formed, sharing a common broad-area metallisation. We use the term “parallel-addressed” micro-LEDs for this type of device. They offer enhancement in surface area to volume ratio, and ready flexibility in number and size of emitting elements. We report on the fabrication of these devices and on their performance compared to conventional broad-area LED’s fabricated from the same wafer. The major issue involved in the fabrication is the interconnection of each individual element, via metallization, as a result of the non-planar device topology. In order to overcome this difficulty involving metal step-height coverage, the sidewalls of the micro-LEDs are made to b
Data Loading...
