Normal Light-emitting Diodes Research Articles

63‐2: Nano‐wire Grid Polarizer and Meta‐surface Textures Integrated High Efficient and Single Polarized Light Emitting Diode

A low power consumption is an essential issue for all of the electrical products, especially for the wearable electrical products, and the liquid crystal displays. This manuscript proposed a single polarized light emitting diode (LED) chip which is used for a direct back light unit for LCD. A wire grid polarizer and a meta‐surface textures are set on the top and bottom of the LED chip in order to obtain a high polarization and transparency. After optimization the potential parameters, the transmittance of TM and the polarization are 93.71% and 99.3% respectively. It can replace the normal LED of direct back light unit in order to obtain a high efficiency of 20% improvement, by comparing liquid crystal display using the APF polarizer. It can be used for reducing power consumption and supply dependence, as well as the cost of displays.

89‐3: Late‐News Paper: High‐Efficiency and Polarized Light Emitting Diode with Wire Grid Polarizer and Meta‐surface Textures

A low power consumption is an essential issue for all of the electrical products, especially for the wearable electrical products, and the liquid crystal displays. This manuscript proposed a single polarized light emitting diode (LED) chip which is used for a direct back light unit for LCD. A wire grid polarizer and a meta‐ surface textures are set on the top and bottom of the LED chip in order to obtain a high polarization and transparency. After optimization the potential parameters, the transmittance of TM and the polarization are 93.71% and 99.3% respectively. It can replace the normal LED of direct back light unit in order to obtain a high efficiency of 20% improvement, by comparing liquid crystal display using the APF polarizer. It can be used for reducing power consumption and supply dependence, as well as the cost of displays.

P‐11.5: Design and Optimization Polarized Light Emitting Diode Chips with Nano‐Wire Grid Polarizer and Meta‐surface Textures

A low power consumption is one of the most important issue for all of the electrical products, especially for wearable products. This manuscript proposed a polarized light emitting diode (LED) chip which is used for a direct back light unit for LCD. A wire grid polarizer and a meta-surface textures are set on the top and bottom of the LED chip in order to obtain a high polarization ratio and transparency. After optimizing the potential parameters, the transmittance of TM and the polarization can reach up to 93.71% and 99.3% respectively. It can replace the normal LED in direct back light unit, and obtain an improved efficiency of 20%, when comparing liquid crystal display with a bottom APF polarizer. It can be used for reducing power consumption and supply dependence, as well as the cost of displays.

Enhanced light extraction from AlGaInP-based red light-emitting diodes with photonic crystals.

The photonic crystal (PC) has been demonstrated to be very effective in improving the extraction efficiency of light-emitting diodes (LEDs). In this paper, high-brightness AlGaInP-based vertical LEDs (VLEDs) with surface PC (SPCLED) and embedded PC (EPCLED) were successfully fabricated. Compared with normal LED (NLED), photoluminescence intensities of SPCLED and EPCLED have been improved up to 30% and 60%, respectively. And the reflection patterns of SPCLED and EPCLED were periodic bright points array, showing the ability to control light in PC. Electroluminescent measurements show that three kinds of LEDs have similar threshold voltages. Simultaneously, the light output power (LOP) of SPCLED and EPCLED has been improved up to 24% and 11% at 200 mA, respectively, in comparison to NLEDs. But the LOP decays earlier for EPCLED due to the excessive heat production. Furthermore, it is demonstrated that the SPCLED and EPCLED luminous uniformity is better. This kind of high brightness PCLED is promising in improving the properties of all kinds of LEDs, especially mini LEDs and micro LEDs.

Efficiency of Light Sources in Trapping Lepidiota Mansueta

Efficiency of six light sources viz., light emitting diode (LED), solar LED, compact fluorescent lamp (CFL), mercury, ultraviolet (UV) and tungsten bulbs in trapping of adult Lepidiota mansueta Burmeister was evaluated in Majuli river island of Assam during 2015-17. Results revealed that the maximum number of beetles (781.2; sex ratio: 3.7:1) got trapped in solar LED light trap and it was found to be significantly superior over the other light sources. With CFL bulbs, the maximum number of beetles were trapped in 15-watt bulb (725.3; sex ratio: 4.1:1). In mercury and UV lamp it was 389.2 and 199.1 beetles with a male: female sex ratio of 4.4:1 and 4.4:1, respectively. Relatively less beetles were attracted to the light traps with tungsten and normal LED bulbs. Based on these observations, a modified battery-operated LED light trap was designed and its performance was compared with solar LED and 15-watt CFL bulb during 2017. The modified battery-operated light trap trapped 427.3- 469.3 beetles as compared to the ones with solar LED (641.0) and 15-watt CFL bulb (582.0).

Epitaxial Growth of InGaN Multiple-Quantum-Well LEDs With Improved Characteristics and Their Application in Underwater Optical Wireless Communications

InGaN light-emitting diodes (LEDs) grown with a thin GaN barrier and a gradually reduced well width in the multiple-quantum-well (MQW) regions close to n-GaN are proposed for use in underwater optical wireless communications. Experimentally, LED epiwafers grown by metal–organic vapor phase epitaxy were found to have comparable crystalline quality despite using a different epistructure design from InGaN MQWs. The modified MQWs facilitated hole transport to the deep quantum wells while preventing energetic electrons from accumulating at the topmost quantum wells close to p-GaN, thus improving the current-light output performance at high currents. In addition, relatively strong carrier localization in the proposed LEDs indicates more injected carriers within the modified MQWs can participate in radiative recombinations to contribute to light output. On the other hand, the available bandwidth of a line-of-sight LED-based optical link passing through a 100-cm-long water tank was found to be around 148.7 MHz using the proposed LED, which is $1.3\times $ higher than that obtained using normal LED. This type of optical link produces data transmission at rates in tap water exceeding 300 Mbit/s and enables real-time transmission of digital TV signals.

Influence of photo-generated carriers on current spreading in double diode structures for electroluminescent cooling

Current crowding close to electrical contacts is a common challenge in all optoelectronic devices containing thin current spreading layers (CSLs). We analyze the effects of current spreading on the operation of the so-called double diode structure (DDS), consisting of a light emitting diode (LED) and a photodiode (PD) fabricated within the same epitaxial growth process, and providing an attractive platform for studying electroluminescent (EL) cooling under high bias conditions. We show that current spreading in the common n-type layer between the LED and the PD can be dramatically improved by the strong optical coupling between the diodes, as the coupling enables a photo-generated current through the PD. This reduces the current in the DDS CSL and enables the study of EL cooling using structures that are not limited by the conventional light extraction challenges encountered in normal LEDs. The current spreading in the structures is studied using optical imaging techniques, electrical measurements, simulations, as well as simple equivalent circuit models developed for this purpose. The improved current spreading leads further to a mutual dependence with the coupling efficiency, which is expected to facilitate the process of optimizing the DDS. We also report a new improved value of 63% for the DDS coupling quantum efficiency.

Optimized photoelectric receiver to enhance modulation bandwidth of visible light communication system

In the visible light communication (VLC) system which combines lighting and communication functions, the 3-dB modulation bandwidth is mainly limited by the light-emitting diode (LED) suffered high-frequency response attenuation. An optimized photoelectric receiver was proposed to enhance the 3-dB modulation bandwidth. The frequency response of the photoelectric receiver was derived. Theoretical analysis predicted that a gain peak would appear in the high-frequency response of the photoelectric receiver. The value of the gain and the frequency point of the gain peak can be adjusted by selecting appropriate values of feedback resistor and capacitor. Then, the measurement platform of 3-dB modulation bandwidth for blue-LED VLC system was established. Experimental measurements demonstrated that the photoelectric receiver with proper sets of feedback resistor and capacitor can compensate the high-frequency response attenuation of a normal LED. The 3-dB modulation bandwidth obtains 56% enhancement if the photoelectric receiver was replaced from a commercial one to our optimized design. In order to further expand the 3-dB modulation bandwidth, an equalization circuit consists of two-stage transistor amplifier and an emitter-follower was introduced to suppress the low-frequency response. The 3-dB modulation bandwidth for the VLC system with our optimized photoelectric receiver can be expanded to 241 or 281 MHz, while the circuit was, respectively, arranged as pre-equalization or post-equalization.

Improved Light Output Power of Chemically Transferred InGaN/GaN Light‐Emitting Diodes for Flexible Optoelectronic Applications

Recent needs of semiconductor lighting sources have pursued diverse functionalities such as flexibility and transparency under high quantum efficiency. Inorganic/organic hybrid light‐emitting diodes (LEDs) are one way to meet these requirements. Here, we report on flexible III‐nitride‐based LEDs and the improvement of their electrical and optical properties. To realize high light emission power and stable current operation, high‐quality epitaxy and elaborate chip processing were performed. The fabricated flexible LEDs showed over threefold optical output power compared to normal LEDs on Si and had comparable forward voltage and series resistances.

Non-Destructive Inspection Methods for LEDs Using Real-Time Displaying Optical Coherence Tomography

In this study, we report the applicability of two different Optical Coherence Tomography (OCT) technologies for inspecting Light Emitting Diode (LED) structures. Sectional images of a LED were captured using a Spectral Domain OCT (SD-OCT) system and a Swept Source OCT (SS-OCT) system. Their center wavelengths are 850 and 1,310 nm, respectively. We acquired cross-sectional two dimensional (2D) images of a normal LED and extracted sectional profiles to inspect possible wire disconnection that may be present in the LED manufacturing process. The SD-OCT and SS-OCT images were compared with each other in the same sample to study their advantages. The distribution of fluorescence material was observed more clearly with the SD-OCT of 850 nm wavelength, whereas the status of wire connection was clearer in the SS-OCT images with 1,310 nm wavelength. In addition, the volume of the fluorophore space was calculated from the OCT images. This is the first report that a nondestructive optical imaging modality such as OCT can be applied to finding screen defects in LED. We expect this method can improve the inspection efficacy over traditional inspection methods such as Charged Coupled Device (CCD) camera or X-ray instruments.

High-performance and current crowding-free InGaN-GaN-based LEDs integrated by an electrically-reverse-connected Schottky diode and a Mg-delta doped p-GaN

This work demonstrates high-performance and current crowding-free InGaN/GaN light-emitting diodes (LEDs) using an electrically-reverse-connected Schottky diode (SD) and an Mg-delta (δ) doped layer. Possible mechanism of carrier transport at the interface between transparent conducting electrode (TCE) and p-GaN with the δ-doped layer is also investigated. Results show that the LED with the SD and Mg delta (δ)-doping layer yields lower series resistance, higher output power, and lower reverse leakage current compared to normal LEDs. In addition, unlike the normal LED, there is no occurrence for the current crowding effect in the proposed LED even at high current density of 380 mA/cm2. These remarkable behaviours clearly indicate that the use of the SD and δ-doping in the p-GaN region is very promising to achieve high-brightness and excellent-reliability GaN-based LEDs.

Degradation mechanism of light‐emitting diodes on patterned sapphire substrate

AbstractWe have investigated possible degradation mechanism for patterned sapphire substrate (PSS)‐based blue light‐emitting diodes (LEDs) using an acceleration burn‐in test under high current stress. Normal LEDs without a PSS had also been compared. Measurements showed that the PSS‐LED has lower series resistance and higher output power compare to those of the normal LED. The acceleration test (@ 490 mA/cm2) results showed that the normal LED suffers from current crowding irrespective of acceleration time while the PSS LED endures up to 100 s. In addition, the estimated lifetime of the PSS‐LED is 1.6 times as high as that of the normal LED at high electrical stress of 490 A/cm2, indicating that the PSS‐LED shows excellent reliability characteristics. Based on electrical/optical measurement results, acceleration test data, and Auger depth profile results, possible degradation mechanism of the PSS‐LED will be discussed in terms of junction temperature (originating from Joule heating), carrier crowding, and p‐contact failure.

Enhanced Luminescence of InGaN Light Emitting Diodes with Strain-Compensated Superlattice Barriers

In this paper, we propose to use the strain-compensated superlattices as the barrier layers within InGaN light emitting diodes (LEDs). High resolution X-ray diffraction measurements indicate good control of the interface quality for the LEDs incorporated with a strain-compensated superlattice barrier (SC-SLB). Furthermore, the thermal activation energy of the LEDs with an SC-SLB in the temperature-dependent photoluminescence (PL) measurements is estimated as about , which is comparable to that of the normal LEDs. This result implies that the amount of crystalline defects, such as threading dislocation, is not significant enough to cause the deterioration of device characteristics. Because of the decrease in the strength of the piezoelectric fields within the multiple quantum wells (MQWs), the LEDs with an SC-SLB exhibit a blueshift and an increased PL intensity as compared to the normal LEDs. The lower quantum-confined Stark effect in the MQWs means that the light output power of the modified LEDs is superior to that of the normal LEDs over the entire operating range. The SC-SLB-containing LEDs also have an improved efficiency drop because the SC-SLB could provide a higher barrier height to suppress the carrier leakage.

High output power GaN-based light-emitting diodes using an electrically reverse-connected p-Schottky diode and p-InGaN–GaN superlattice

We demonstrate the high-performance and excellent reliability characteristics of InGaN–GaN light-emitting diodes (LEDs) using an electrically reverse-connected p-Schottky diode and p-InGaN–GaN superlattice (SL). Measurements show that the LED with the Schottky diode and SL yields lower series resistance and higher output power compared to normal LEDs. In addition, the device degradation rate of the proposed LED is 33 times as low as that of the normal LED at high electrical stress of 410 A/cm2, indicating excellent reliability behavior. These results mean that the use of p-Schottky diode and p-SL is very promising for the realization of high-performance GaN-based LEDs.

Improved Light Extraction Efficiency of InGaN-Based Light-Emitting Diodes with Patterned n-GaN Substrate

We improved the light extraction efficiency of InGaN-based light-emitting diodes (LEDs) in which an n-type GaN layer was patterned onto a sapphire substrate with nano-sized SiO2 columns. Indium tin oxide thin layer deposition on a SiO2 layer followed by wet etching gives rise to oxide self-assembled clusters of 100–400 nm size and a subsequent SiO2 etching with an oxide mask results in SiO2 columns on an n-type GaN layer. The output power of the patterned n-GaN substrate (PNS) LED shows a 1.33 time increase compared with that of a normal LED without an n-GaN pattern when the total output power emitted in all directions from the packaging LED was measured under a current injection of 20 mA. The increase in output power from the PNS LED depends on the size of the SiO2 columns on the n-type GaN substrate.

InGaN Light-Emitting Diode With Quasi-Quantum-Dot-Shaped Active Layer Using SiCN Interfacial Layer

A quasi-quantum-dot (QQD)-shaped InGaN-GaN multilple-quantum-well light-emitting diode (LED) was achieved using a silicon carbon nitride (SiCN) interfacial layer. QQDs with ~100-nm diameter and ~4-nm height were uniformly formed inside the InGaN active layer due to strain and affinity difference between the InGaN and SiCN layer. The surface morphology and structural properties of QQD-LED were measured with atomic force microscopy, secondary ion mass spectrometry, and X-ray diffraction. Device performance of QQD-LEDs were evaluated and compared with normal LEDs. The QQD-LED showed ~15% higher photoluminescence intensity and ~10% higher optical output power

Low turn-on voltage and series resistance of polarization-induced InGaN-GaN LEDs by using p-InGaN/p-GaN superlattice

We have demonstrated high-performance InGaN-GaN multiple quantum-wells light-emitting diodes (LEDs) using polarization-induced (PI) p-InGaN-GaN superlattice. Electrical measurements show that PI LEDs produce much lower series resistance and turn-on voltage (at 20 mA) as compared to those of normal LEDs without the superlattice. It is also shown that the output power and photon wavelength of the PI LEDs remain electrically stable up to a high stress region of 200 mA. However, those of normal LEDs become electrically and optically degraded in excess of 120 mA. These results show that the use of the PI effect is very effective to the improvement of the electrical properties of LEDs.

Beveled sidewall formation and its effect on the light output of a <inline-formula><math display="inline" altimg="none" overflow="scroll"><mrow><mi>GaInN</mi></mrow></math></inline-formula> multiquantum well light-emitting diode with sapphire substrate

In this research, experiments and optical simulations are carried out to study the effect of beveled sidewalls and geometric shapes on the light extraction efficiency of a GaN light-emitting diode (LED) with sapphire substrate. In addition to the conventional rectangular chips, hexagonal chips are experimentally processed for the first time on a novel island-like GaN substrate, on which the beveled sidewalls are naturally formed at each island during GaN epitaxial growth on a sapphire original substrate by hydride vapor phase epitaxy (HVPE) technology. The results from our simulations and experiments show that the output power of a LED with beveled sidewalls is about two times that of a normal LED, and those from hexagonal chips are always better than those from conventional rectangular chips.

Nitride-Based LEDs With Textured Side Walls

Nitride-based light-emitting diodes (LEDs) with textured side walls were fabricated. By using plasma-enhanced chemical vapor deposition SiO/sub 2/ layer as the etching mask, we successfully etched the nitride epitaxial layers to achieve wavelike side walls. It was found that such wavelike side walls could mainly enhance the light output at the horizontal directions. With a 20-mA current injection, it was found that the output powers of the LED with textured side walls and normal LED were 9.3 and 8.4 mW, respectively. Furthermore, it was found that such textured side walls will not result in a higher operation voltage.

InGaN/GaN multiple‐quantum‐well dual‐wavelength near‐white light emitting diodes

An InGaN/GaN blue light emitting diode (LED) structure and an InGaN/GaN green LED structure were grown sequentially onto the same sapphire substrate so as to achieve a nitride-based near-white LED. In order to avoid the thyristor effect, we choose a large 1 × 1 mm2 LED chip size, which was six times larger than that of the normal LED. It was found that we could observe a near-white light emission with CIE color coordinates x = 0.2 and y = 0.3, when the injection current was lower than 200 mA. It was also found that the output power, luminous efficiency and color temperature of such a near-white LED were 4.2 mW, 0.8l m/W, and 9000 K, respectively.