Plasmonic structures offer a unique capability to generate electromagnetic oscillation in a tightly confined space at the metal-dielectric interface. This localized intense field can be used to significantly enhance light-matter interaction in an active material. Here, we use a hyperbolic metamaterial resonator on a UV AlGaN multiple quantum well to demonstrate a UV plasmonic nanolaser. The hyperbolic metamaterial consists of metal/dielectric multiple layer structure, which has dielectric permittivity tensor of opposite signs in two orthogonal directions. By proper design, it has an indefinite hyperbolic dispersion. We will discuss the resonator dimension design using this unique hyperbolic dispersion to enhance quantum well radiation for laser operation.
The growth of hexagonal GaN-on-Si(100) sample prepared by pulsed laser deposition (PLD) was employed in the
development of GaN-on-Si technology. In contrast to common GaN-on-sapphire and GaN-on-Si(111) technologies, the
use of the GaN film on Si(100) by PLD provides low-cost and large-area single crystalline GaN template for GaN
applications, via a single growth process without any interlayer or interruption layer. The evolution of GaN growth
mechanism on Si(100) substrate with various growth times is established by SEM and TEM data, which indicated that
the growth mode of the GaN films gradually changes from island growth to layer growth when the growth time increases
up to 2hrs. Moreover, no significant GaN meltback was found on the GaN sample surface due to the high-temperature
operation of PLD. The GaN sample was subjected to MOCVD treatment to regrow a GaN layer. The results of X-ray
diffraction analysis and photoluminescence measurement show the reliability of the PLD-GaN sample and are promising
for the development of the GaN-on-Si technology using PLD technique.
High performance of GaN light-emitting diodes with a finger-type embedded contact (F-LEDs) was demonstrated on a Cu substrate for improved thermal management and increased efficiency. In contrast to common sapphire-based LEDs (C-LEDs) and the wing-type embedded LEDs (W-LEDs), the use of the finger-type embedded contact not only reduces the effect of the current crowding of W-LEDs to achieve a uniform current injection but also eliminates the problem of light shading of C-LEDs to obtain more output power. At 350 mA, the output power of the three LEDs was measured to be 329.39, 284.52, and 236.38 mW for the C-LED, W-LED, and F-LED, respectively; representing that the F-LED in output intensity was raised 39.3% and 20.3% higher than that in the C-LED and the W-LED. Similarly, a 63.61% increase of output power of F-LED was obtained as compared to the C-LED case at 700 mA current injection. At this point, the efficiency droop of F-LED is 33.7%, which is lower than that of 44.1% and 53.5% in W-LED and C-LED, respectively; results are promising for the development of high performance LEDs using the finger-type embedded contact.
High performance 365 nm vertical-type ultraviolet light-emitting diodes (UV-LEDs) were developed using an embedded
self-textured oxide (STO) structure using metal-organic chemical vapor deposition system. From etch-pit-density results,
the dislocation densities of LED epilayers were effectively reduced to 5.6×106 cm-2 by inserting the STO structures due
to the relaxation of residual stress. The vertical-type UV-LEDs are fabricated using a combination technique of metal
bonding and sapphire substrate separation. When the UV-LEDs (size: 45 × 45 mil2) were driven with a 20 mA injection
current, the output powers of the LEDs with and without STO were measured to be 10.2 and 5.51 mW, respectively. The
external quantum efficiency of LEDs with STO exhibits 32% higher than that of LED without STO. As increasing
injection current to 350 mA, a near 45 mW light output was measured from STO-LED sample. This benefit was
attributed to the introduction of STO structure which can not only block the propagation of threading dislocations but
also intensify the light extraction of LED.
High indium content InGaN films were grown on sapphire substrate using low temperature pulsed laser deposition (PLD)
with nitrogen plasma and a specific target. The controllable target consists of two separate sections: an indium sheet with
periodic rectangular-holes and a standard GaN wafer. By changing the rectangular-hole area, a modulated indium vapor
was excited by pulsed laser and introduced into the InGaN deposition reaction, contributing the increase in the
incorporation of indium into the InGaN film. The structural and optical stability of the 33 and 60% indium InGaN
revealed no differences in the line-shape and peak position even after annealing at 800°C for 75 min from x-ray
diffraction and luminescence results. Moreover, such high thermal stability of 60% InGaN film was put in metal organic
chemical vapor deposition (MOCVD) to regrow GaN layer, the peak position of 860 nm remained unchanged after
MOCVD regrowth. The flat and uniform of regrown sample indicates that the PLD method used in this study is indeed
promising for the development long wavelength of high indium content InGaN emitters.
High indium composition InGaN films were co-deposited on u-GaN templates using low temperature (300°C)
pulsed laser deposition (PLD). The du-composition target consisted of a 3-inch indium sheet drilled with periodic
rectangular holes mounted on a normal GaN wafer. By changing the ratio of the holes areas to total sheet area, the
indium concentration in two InGaN films was set to 33% and 60%. The structural and optical characteristics of these
films are investigated through isochronal and isothermal annealing. X-ray diffraction (XRD) and cathodeluminescence
results for the 33% sample exhibited no significant differences in line-shape and peak position even after annealing at
800°C for 100 minutes. In contrast, the XRD peak of 60% sample became broadened under the same annealing condition.
This slight inhomogeneity in composition also resulted in two visible peaks in the photoluminescence spectrum.
Although the optical properties of the 60% sample can be considered merely acceptable, the advantages of applying PLD
to the growth of high thermal stability and high indium composition InGaN have been made clear. The PLD technique
shows promise for developing long wavelength devices.
High performance 375-nm ultraviolet (UV) InGaN/AlGaN light-emitting diodes (LEDs) was developed using a
heavy Si-doping technique with metalorganic chemical vapor deposition (MOCVD). From the transmission electron
microcopy (TEM) image, the dislocation density was reduced after inserting a heavily Si-doping growth mode transition
layer (GMTL) between un-doped GaN layer and Si-doped Al0.02Ga0.98N contact layer. The internal quantum efficiency
(IQE) of the sample with GMTL measured by power-dependent photoluminescence shows 39.4% improved compared
with the sample without GMTL. When the vertical type LED chips (size: 1mm×1mm) driving by a 350-mA current, the
output powers of the LEDs with and without GMTL were measured to be 286.7 mW and 204.2 mW, respectively. As
much as 40.4% increased light output power was achieved. Therefore, using the GMTL to reduce dislocation defects
would be a promising prospective for InGaN/AlGaN UV LEDs to achieve high internal quantum efficiency.
The characteristics of high voltage LED consisted of an array of 64 micro-cells GaN LEDs was investigated through
using different substrate. In this study, two kinds of high voltage LEDs are presented; one is grown on sapphire
substrate and the other one is on mirror/Si substrate. The output power of high voltage LEDs with sapphire and
mirror/Si substrate is 170 and 216 mW at an injection current of 24 mA, respectively. The LEDs on mirror/Si
substrate leads to the superior performance in output power as compared with one on sapphire substrate is attributed
to the improvement of thermal dissipation and light extraction.
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