The use of Polystyrene Spheres (PSs) to realize nano-roughened Indium-Zinc Oxide (IZO) surface and a high
reflective ohmic p-contact to improve the optoelectronic properties of larger-area (1×1 mm2) vertical metallic-substrate
GaN-based light-emitting diodes (VLEDs) were proposed and investigated. A metal system consisting of annealed-
Pt/Al/Pt was employed to serve as a reflector and ohmic contact to p-GaN, which exhibits a good ohmic contact
(1.84×10-3 Ωcm2) and high reflectivity (88% at 465 nm). After the removal of sapphire using laser lift-off process (LLO)
and etching of u-GaN by ICP, Ti/IZO film was then deposited to serve as a transparent conduction layer (TCL). After
that, the polystyrene spheres (PSs) were dispersed on the IZO surface, followed by second sputtering-deposition of IZO
film to fill the space between neighboring PSs. The PSs were then removed to form a nano-roughened IZO top-layer.
Compared to regular VLEDs with Ni/Au ohmic contact and Ti/Al/Ti/Au as reflector layer, the fabricated VLED shows a
typical increase in light output power (i.e., ▵Lop/Lop) by 72.2% at 350 mA and a decrease in forward voltage (Vf) from
3.43 V down to 3.33 V. It is expected that the proposed PSs nano-roughening technology and high reflection annealed-
Pt/Al/Pt metal system for ohmic contact to p-GaN would be a potential candidate for the fabrication of high power GaNbased
LEDs for solid-state lighting in the near future.
Use of deep ultraviolet (248 nm) KrF laser irradiation to roughen vertical GaN-based LEDs surface with volcanolike
protrusions for light output (Lop) improvement was proposed and demonstrated. After pulse irradiations of KrF laser
(750-850 mJ/cm2), the rate of electron-hole pair recombination at sites with dislocation defects is greater than for
crystalline GaN, favoring for the formation of GaOx, and in turn, resulting in a relatively lower etching rate therein and
leading to a roughened surface with volcano-like protrusions. Typical diameter/height and density of protrusions are
around 2~4 μm/2 μm and 106 cm-2. Through the use of KrF laser and KOH etching, an enhancement in the root-meansquare
surface roughness by 250 times and an improvement in Lop by 25% at 750 mA were obtained. It is expected that
the surface roughness of Gallium Nitride by KrF excimer laser technology would be a potential candidate for the
fabrication of high power GaN-based LEDs for solid-state lighting in the near future.
In this study, well-ordered and vertically-aligned metal (nickel (Ni)/zinc (Zn)) and metal oxides (NiO/ZnO) nano
heterojunctions (NHJs) were grown inside the nanopores of anodic aluminum oxide template (AAOT) using electrochemical
deposition (ECD) and thermal oxidization. The prepared NHJs are with a controllable length and diameter. The
electrical properties of NiO/ZnO NHJs show a rectifying behavior of a p-n junction, while the Ni/Zn NHJs show an
ohmic behavior. The optoelectronic characteristics demonstrate that the NiO/ZnO NHJs have fairly good sensitivity and
response to the ultraviolet (UV) light (366 nm) with decrease in Vth by about 75% and an increase in Jr by about 80% @
6 mW/cm2. The low dimension of NHJs shows profound quantum confinement effect, which would be potential
applications on nano integrated photonics, such as photodetectors, optical sensors and biosensors.
This study proposes the use of a ZnO-nanowire (ZnO-NW)-based heterojunction structure for applications of nano
optoelectronic sensors and photovoltaic devices. Nano heterojunctions (NHJs) were formed via e-beam deposition of ptype
nickel oxide (NiO) onto the vertical-aligned ZnO-NWs grown by hydro-thermal growth method. The dark J-V curve
shows that the prepared NiO/ZnO-NWs NHJ has a diode-like behavior with a forward threshold voltage (Vth) of 1.2 V
and a leakage current (Jr at -1V) of 0.02 μA/cm2, respectively. It also exhibits a superior response to UV (366 nm) and
AM 1.5G light illuminations. The Vth and the photocurrents (i.e., Jr at -1V) under UV (366 nm @ 6 mW/cm2) and AM
1.5G light were 0.7 V/0.06 μA/cm2 and 0.5 V/ 3.2 μA/cm2, respectively, revealing an increase in the diode current of
about 3× and 160×, respectively.
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