In vivo optogenetics provide special and powerful capabilities in regulation of neurons, research of neural circuits and even in treatment of brain diseases. However, conventional hardware for such studies tethers the experimental animals to remote light sources, power sources, or other functional modules, which imposes considerable physical constrains on natural behaviors and limits the range of the experiment. To enable flexible and convenient optogenetic manipulation of neural circuit with finite disruption of animal behavior, a wirelessly powered optoelectronic device, composing mainly of a radio frequency (RF) energy harvester and a high-performance GaN-based light-emitting diode (LED), is demonstrated and can be used to construct an implantable optrode for optogenetics. The wireless RF power signal is collected through an antenna and a two-stage voltage doubling rectifier circuit, and finally converted into high-amplitude DC voltage. Provided with 25-dBm RF power with a distance of 0.2 m, the RF energy harvesting and processing circuit can output a stable 2.81 V DC voltage and drive the designed GaN-based LED to work normally. After being successfully lit, the emission peak wavelength of the LED locates 455 nm and the output optical power density reaches 214.9 mW / mm2, which is fully capable of activating light-sensitive ion channel channelrhodopsin-2. The total area of the device is 3 mm × 3.2 mm, which is suitable for subdermal implantation.
As efficient artificial light sources, nitride-based light-emitting diodes (LEDs) have been widely used. However, III nitride white light-emitting diodes (WLEDs) are mostly fabricated by combining a blue LED chip with yellow phosphors, which results in inevitable problems, such as low color-rendering index (CRI) and detrimental effect to human eyes. As a solution for healthy lighting, we report a strategy to produce a WLED with an emission spectrum perfectly matched with natural daylight. By utilizing near-ultraviolet LED chips and a mixture of blue/cyan/amber/red phosphors, a CRI (Ra) of 97.9 is achieved for the WLEDs at a correlated color temperature of around 5000 K. The resemblance ratio of these solar-spectrum WLEDs with the standard normalized daylight spectrum (5000 K) is found to as high as 93.4%. Residual UV light in the normalized spectrum is <5 % . The method will benefit the development of high-efficiency healthy artificial light sources.
We have successfully fabricated 7-μm 155-nm-thick undercut microdisk cavities with AlN / Al0.60Ga0.40N (5.5 nm / 2.5 nm) multiple quantum wells epitaxially grown on Si substrate by metal–organic chemical vapor deposition. Upon optical pumping, whispering-gallery modes (WGMs) with wavelengths around ∼250 nm can be observed throughout the photoluminescence spectrum at room temperature, with quality factors around 500 to 1000. These cavity modes have been analyzed by theoretical calculations. Our results suggest great potentials to demonstrate WGM lasing in the UVC range from these AlGaN/AlN-on-Si microdisk cavities monolithically grown on a Si platform.
In this paper, an array of blue LEDs with high optical power was presented and discussed. Optical of the novel design
was completed with the help of running simulation in TracePro to predict the performance of the module. 36 Cree XP-E
blue LEDs with a square reflector were used in the novel design. Optical simulation obtained from TracePro showed that
the total optical power of the LED array could reach 16.83W. To verify the simulation results, Aluminum PCB, Copper
PCB and Aluminum square reflector have been made respectively. Firstly, 36 Cree XP-E blue LEDs with small-pitch
were fixed on each PCB, then; an Aluminum square reflector was assembled on each PCB. This optical module was
installed on a radiator and tested. The optical output power of sample 1 used Aluminum PCB and Aluminum reflector
and sample 2 used Copper PCB and Aluminum reflector was 8.126W and 9.445W at 2A, respectively. It could be
observed that the optical output power of sample 2 was higher than that of sample 1. It could be attributed to the better
thermal dispersion performance of Copper. In order to improve the light reflectivity and reduce the loss of light, ultrathin
silver was coated on the Aluminum reflector by electron beam evaporation. The optical output power of sample 3 used
Copper PCB and silver-plated Aluminum reflector was 12.541W at 2A. A uniform square spot with high optical power
Thanks to the development in epitaxial growth, chip fabrication and packaging of LEDs, emission spectral of the device
is capable of covering the visible spectrum. Therefore, Light-emitting diode (LED) is currently undergoing a growing
interest in many applications, such as lighting. Besides lighting, LEDs offer a wide range of potential applications
including display. In contrast with LCD, LEDs display has better contrast ratio, higher response rate etc which makes
LEDs along with other self-illumination technologies an ideal candidate in making display panel. Due to the
popularization of HD and Ultra HD standard, display panel with better image quality is needed which means the number
of pixels of the panel needs to be increased while the size of each pixel needs to be minimized. In this paper, we describe
the design and fabrication of a colour tuneable and addressable LED micro display based on a 16×16 and 32×32 LED
matrixes with typical pixel size of 0.7 and 0.5mm respectively.
We investigate the relation between the thickness of sapphire substrates and the extraction efficiency of LED. The
increasing about 5% was observed in the simulations and experiments when the sapphire thickness changed from 100μm
to 200μm. But the output power increasing is inconspicuous when the thickness is more than 200μm. The structure on
bottom face of sapphire substrates can enhance the extraction efficiency of GaN-based LED, too. The difference of
output power between the flip-chip LED with smooth bottom surface and the LED with roughness bottom surface is
about 50%, where only a common sapphire grinding process is used. But for those LEDs grown on patterned sapphire
substrate the difference is only about 10%. Another kind of periodic pattern on the bottom of sapphire is fabricated by the
dry etch method, and the output of the back-etched LEDs is improved about 50% than a common case.
Different types of dielectric optical coatings for GaN based high bright LEDs were designed and discussed. The optical
coatings included the anti-reflection (AR) coating, high-reflection (HR) coating, and omni-directional high reflection
coating. Main materials for the optical coatings were dielectric materials such as SiO2, Ta2O5 and Al2O3, which were
different from the metallic reflector such as Ag usually used now. For the application of anti-reflection coating in GaN
LEDs, it was introduced into the design of transparent electrodes with transparent materials such as ITO to form
combined transparent electrodes. With the design of P, N transparent electrodes using the AR coating and ITO for GaN
LEDs, the extraction efficiency was improved by about 15% experimentally. For the dielectric high-reflection coating, it
has higher reflectivity and lower absorption than the metal reflector, and it was supposed to improve the extraction
efficiency obviously. While the dielectric omni-directional reflection coating using dielectric materials was also designed
and discussed in this article, since which was anticipated to improve the extraction efficiency furthermore. Using SiO2
and Ta2O5, the average reflectivity of a design of all dielectric omni-directional high reflection coating on the sapphire
surface was over 94%.
The effects of plasma induced damage in different conditions of ICP and PECVD processes on LEDs were presented.
For ICP mesa etch, in an effort to confirm the effects of dry etch damage on the optical properties of p-type GaN, a
photoluminescence (PL) measurement was investigated with different rf chuck power. It was founded the PL intensity of
the peak decreased with increasing DC bias and the intensity of sample etched at a higher DC bias of -400V is less by
two orders of magnitude than that of the as-grown sample. Meanwhile, In the I-V curve for the etched samples with
different DC biases, the reverse leakage current of higher DC bias sample was obviously degraded than the lower one. In
addition, plasma induced damage was also inevitable during the deposition of etch masks and surface passivation films
by PECVD. The PL intensity of samples deposited with different powers sharply decreased when the power was
excessive. The PL spectra of samples deposited under the fixed condition with the different processing time were
measured, indicating the intensity of sample deposited with a lower power did not obviously vary after a long time
deposition. A two-layer film was made in order to improve the compactness of sparse dielectric film deposited with a
In this paper we studied the influence of N electrode on the extraction efficiency of high power light-emitting diodes
(LEDs). Simulation and experimental results show that comparing with traditional metal N electrodes the extraction
efficiency of LEDs with transparent N electrode is increased by 15%, and it is easier in process than the other techniques.
So we proposed a new kind of strip LEDs with transparent electrodes on both P-GaN and N-GaN. The design of
transparent electrodes was trade-off between transmittance and resistance. At the same time, the strip structure has some
advantages over the traditional square LEDs, which can increase the extraction efficiency and reduce the thermal
resistance. Antireflective and high reflective optical coatings were also used in this design. The fabrication of LEDs with
transparent electrodes on both P-GaN and N-GaN has been demonstrated. The output power of blue LEDs is 240mW at
350mA, forward voltage is below 3.5V. The luminous flux of white LEDs reached 65lm at 350mA.