Progress in Violet Light-Emitting Diodes Based on ZnO/GaN Heterojunction

Abstract

Progress in light-emitting diodes (LEDs) based on ZnO/GaN heterojunctions has run into several obstacles during the last twenty years. While both the energy bandgap and lattice parameter of the two semiconductors are favorable to the development of such devices, other features related to the electrical and structural properties of the GaN layer prevent an efficient radiative recombination. This work illustrates some advances made on ZnO/GaN-based LEDs, by using high-thickness GaN layers for the p-region of the device and an ad hoc device topology. Heterojunction LEDs consist of a quasicoalesced non-intentionally doped ZnO nanorod layer deposited by chemical bath deposition onto a metal–organic vapor-phase epitaxy -grown epitaxial layer of p-doped GaN. Circular 200 μm-sized violet-emitting LEDs with a p-n contact distance as low as 3 μm exhibit a turn-on voltage of 3 V, and an emitting optical power at 395 nm of a few microwatts. Electroluminescence spectrum investigation shows that the emissive process can be ascribed to four different recombination transitions, dominated by the electron-hole recombinations on the ZnO side.

Ultraviolet electroluminescence with electrically tunable colour from epitaxial n-(0001)ZnO/p-(0001)GaN light-emitting diodes

“…Many groups have reported the * Author to whom any correspondence should be addressed. fabrication of n-ZnO/p-GaN junction based LEDs, where various growth techniques, such as molecular beam epitaxy [3], metalorganic chemical vapour deposition [4], chemical bath deposition [5], RF magnetron sputter [6] and pulsed laser deposition (PLD) [7], are used to grow the ZnO layer. Emission of light in the wavelength range of 390-415 nm has also been observed from these devices [5,[8][9][10].…”

“…fabrication of n-ZnO/p-GaN junction based LEDs, where various growth techniques, such as molecular beam epitaxy [3], metalorganic chemical vapour deposition [4], chemical bath deposition [5], RF magnetron sputter [6] and pulsed laser deposition (PLD) [7], are used to grow the ZnO layer. Emission of light in the wavelength range of 390-415 nm has also been observed from these devices [5,[8][9][10]. Recently Ai et al [3] and Turko et al [11] have reported UV light emission from n-ZnO/p-GaN heterojunction LEDs that peak at ∼376 nm and 366 nm, respectively.…”

Enhancement of the near-band-edge electroluminescence from the active ZnO layer in the ZnO/GaN-based light emitting diodes using AlN-ZnO/ZnO/AlN-ZnO double heterojunction structure

“…Accordingly, the crystalline p-GaN epilayer with the structure matching to the ZnO material becomes a substitution material for hetero-contacting to n-ZnO film. Although the resulting n-ZnO/p-GaN heterojunction diode showed better diode rectification and photo-electric conversion efficiency as compared to the ZnO-based homojunction diode [12][13][14][15][16][17], structural optimization to confine the device active layer in the n-ZnO layer as well as improvement of its crystallinity is still ongoing. For example, Long et al fabricated an MgZnO/ZnO/MgZnO double heterojunction (DH) structure on the p-GaN epilayer layer using a radio frequency (rf) magnetron sputtering system to confine the injection carriers in the ZnO layer.…”

Effect of the Si doping on the properties of AZO/SiC/Si heterojunctions grown by low temperature pulsed laser deposition

“…Because of its non-toxicity, abundance, and availability in the earth, ZnO is considered very attractive in various technological fields. Moreover, the optical and electrical properties of ZnO and AZO thin films, strongly dependent on the specific growth technique and the processing conditions, make them appealing for many optical, electronic and optoelectronic applications such as transparent and conductive windows [11], memristors [12,13], photocatalysis [14][15][16], photoconductive detectors [17] and antennas [18], UV photodetectors and gas sensors [19], solar cells [20][21][22] and solar heterojunctions [23], and light emitting diodes [24][25][26].…”