Oblique electron-beam evaporation of distinctive indium-tin-oxide nanorods for enhanced light extraction from InGaN/GaN light emitting diodes

Abstract

This paper presents a novel and mass-producible technique to fabricate indium-tin-oxide (ITO) nanorods which serve as an omnidirectional transparent conductive layer (TCL) for InGaN/GaN light emitting diodes (LEDs). The characteristic nanorods, prepared by oblique electron-beam evaporation in a nitrogen ambient, demonstrate high optical transmittance (T>90%) for the wavelength range of 450nm to 900nm. The light output power of a packaged InGaN/GaN LED with the incorporated nanorod layer is increased by 35.1% at an injection current of 350mA, compared to that of a conventional LED. Calculations based on a finite difference time domain (FDTD) method suggest that the extraction enhancement factor can be further improved by increasing the thickness of the nanorod layer, indicating great potential to enhance the luminous intensity of solid-state lighting devices using ITO nanorod structures.

Indium tin oxide nanowires growth by dc sputtering

“…However, the lack of catalyst does not necessarily exclude the possibility of vapor-liquidsolid (VLS) growth mechanism. It was proposed that the growth mechanism of ITO nanorods by e-beam deposition is self-catalytic VLS growth [6,13]. Metals with low melting point can easily form droplets for self-catalyzed VLS growth of the nanowires [17], so that it is possible that the growth mechanism is indeed self-catalyzed VLS.…”

“…Although ITO used in practical applications is mainly in the thin film form, there is considerable interest in ITO nanostructures [4][5][6][7][8][9][10][11][12][13][14][15][16], since they can result in very low resistivity [4], as well as enable improved performance of solar cells due to improved charge collection [6]. Growth of ITO nanostructures using different methods has been reported [4][5][6][7][8][9][10][11][12][13][14][15][16], such as chemical vapor deposition [4,8,10,14,15], chemical synthesis [5], oblique-incidence electron-beam (ebeam) deposition [6,13], sol electrophoresis [7], sputtering [9,11], and thermal treatment [12].…”

“…Growth of ITO nanostructures using different methods has been reported [4][5][6][7][8][9][10][11][12][13][14][15][16], such as chemical vapor deposition [4,8,10,14,15], chemical synthesis [5], oblique-incidence electron-beam (ebeam) deposition [6,13], sol electrophoresis [7], sputtering [9,11], and thermal treatment [12]. Some of these methods, such as chemical vapor deposition [4,8,10,14,15] and thermal treatment [12], require a high growth temperature and thus would not be suitable for growth on glass substrates, which are of interest for low cost optoelectronic device applications.…”

“…On the other hand, low temperature methods like chemical synthesis [5] result in free-standing nanostructures instead of nanorod/nanowire arrays/networks on the substrate. In some cases, the use of templates was needed for the ITO nanostructure growth [7,11], while reports on the ITO nanorod/nanowire growth using conventional techniques such as e-beam deposition [6,13] and sputtering [9] have been scarce. While e-beam deposition was performed at oblique incidence [6,13], dc sputtering deposition was simpler, but it resulted in relatively low density of ITO "whiskers" with diameters 10-20 nm and lengths 500 nm-1 µm [9].…”

A Mini Review: Antireflective Coatings Processing Techniques, Applications and Future Perspective

“…The deep-UV optical devices are needed in flame monitoring, optical fibres, interferometric lithography, detectors lenses or femtosecond lasers [125] . Earlier, various research groups remarkably improves the LED efficiency using AR coatings such as UV-LED of GaN doubles the efficiency at 365 nm wavelength [126] , Al 2 O 3 -InP/InGaAsP LEDs for optical communications [127] , LEDs-optical lenses [128] Al 2 O 3 -TiO 2 AR coating for red light organic electroluminescent devices [129] , Al nanoparticles by co-sputtering for GaN-LEDs [130][131][132] Al 2 O 3 -ZnO 2 GaN-LEDs [133][134][135][136] , ZnO 2 -LEDs [132,135] , Indium tin Oxide nanorods for LEDs [137][138][139][140] . Some of these methods are applicable commercially, but few of them are restricted to labs due to costly groundwork, difficult process and damaged induced procedure while few techniques limited to small area LEDs with minor current values.…”