Preface to the Special Topic on Compound Semiconductor Materials and Devices on Si

The research in silicon photonics has been booming due to its potential for lowcost,reliable,energy-efficient and high-density chip-wise integration using widely available CMOS technology,featuring the tremendous success in modulator,detector and other passive waveguide components in industry.However,the absence of efficient and reliable electrical to optical converter on Si platform has been considered as“the last piece of the puzzle”,hindered by the in-direct bandgap property of Si bulk materials.CompoundⅢ–Ⅴsemiconductor devices offer highly efficient optical light emitting sources and optical amplifiers,hence the compound semiconductor materials and devices on Si platform are drawing more and more attention nowadays as it could make possible the long-dreamed light sources on Si substrates by combining their advantages with silicon ICs,enabling the fabrication of full functional optoelectronic circuits,chip-to-chip and even system-to-system optical chips.     

History,current developments,and future directions of near‐field optical science

This paper reviews the science of the optical near-field(ONF),which is created and localized in a nanometer-sized material(NM)or on its surface.It is pointed out that work on near-field optics was started in order to break through the diffraction limit in optical microscopy and had already come to an end without giving answers to the essential questions on the origin of the near-field optical interaction.However,recent studies have reincarnated these studies and identified the ONF as an off-shell quantum field.Based on this identification,a novel science called off-shell science has started on the basis that the dispersion relation between energy and momentum is invalid for the ONF.This quantum field is called the dressed photon because it is created as a result of the interaction between photons and electrons(or excitons)in a NM and,thus,it accompanies the energies of electrons or excitons.In reviewing current developments,this paper presents fifteen novel phenomena that are contrary to the common views in conventional optical science.Novel technologies developed by applying these phenomena are also reviewed.These include:nanometer-sized optical devices,nano-fabrication technology,and energy conversion technology.High-power Si light emitting diodes,Si lasers,and SiC polarization rotators are reviewed as examples of electrical to optical energy conversion.For future directions,this paper also reviews novel theoretical studies that have commenced recently by relying on physical and mathematical bases.     

A STUDY OF Zn DIFFUSION IN InP AT LOW TEMPERATURE

The diffusion of Zn in InP at low temperature is investigated.The experiment is accomplishedin an evacuated and sealed quartz ampoule using Zn_3P_2 as the source of Zn.The electrical characteristics of the diffusion samples obtained by the isotemperature processand the two-temperature process have been compared.It is found that with the two-temperatureprocess one can obtain a smooth,damageless and high-concentration surface layer.This processhas been applied to fabricate InGaAsP/InP light emitting diodes,and the diodes obtained have anoutput power of≥1mW with a series resistance of 2—5Ω.The behaviors of Zn diffusion in InPare discussed.     

Large-scale,adhesive-free and omnidirectional 3D nanocone anti-reflection films for high performance photovoltaics

An effective and low-cost front-side anti-reflection(AR) technique has long been sought to enhance the performance of highly efficient photovoltaic devices due to its capability of maximizing the light absorption in photovoltaic devices. In order to achieve high throughput fabrication of nanostructured flexible and anti-reflection films, large-scale, nano-engineered wafer molds were fabricated in this work. Additionally, to gain in-depth understanding of the optical and electrical performance enhancement with AR films on polycrystalline Si solar cells, both theoretical and experimental studies were performed. Intriguingly,the nanocone structures demonstrated an efficient light trapping effect which reduced the surface reflection of a solar cell by17.7% and therefore enhanced the overall electric output power of photovoltaic devices by 6% at normal light incidence. Notably, the output power improvement is even more significant at a larger light incident angle which is practically meaningful for daily operation of solar panels. The application of the developed AR films is not only limited to crystalline Si solar cells explored here, but also compatible with any types of photovoltaic technology for performance enhancement.     

High performance Ga N-based hybrid white micro-LEDs integrated with quantum-dots

Hybrid white micro-pillar structure light emitting diodes(LEDs)have been manufacture utilizing blue micro-LEDs arrays integrated with 580 nm CIS((CuInS2-ZnS)/ZnS)core/shell quantum dots.The fabricated hybrid white micro-LEDs have good electrical properties,which are manifested in relatively low turn-on voltage and reverse leakage current.High-quality hybrid white light emission has been demonstrated by the hybrid white micro-LEDs after a systemic optimization,in which the corresponding color coordinates are calculated to be(0.3303,0.3501)and the calculated color temperature is 5596 K.This result indicates an effective way to achieve high-performance white LEDs and shows great promise in a large range of applications in the future including micro-displays,bioinstrumentation and visible light communication.     

Temperature dependence of excitonic transition in ZnSe/ZnCdSe quantum wells

In recent years ,the interest in the quantum hetero-structures composed of theⅡ-Ⅵwide gap materials haveincreased dueto potential device applications ,suchasthehigh-brightness blue/green light emitting diodes(LEDs) andlaser diodes (LDs)[1].Sincethe applicationof semiconductor materials to optoelectronic devices re-quires a precise design of the optical properties at theoperation temperature, it is i mportant to have theknowledge of the temperature effects on the opticalproperties of the mat…     

Progress of Si-based Optoelectronic Devices

Si-based optoelectronics is becoming a very active research area due to its potential applications to optical communications. One of the major goals of this study is to realize all-Si optoelectronic integrated circuit. This is due to the fact that Si- based optoelectronic technology can be compatible with Si microelectronic technology. If Si - based optoelectronic devices and integrated circuits can be achieved, it will lead to a new irtformational technological revolution. In the article, the current developments of this exciting field are mainly reviewed in the recent years. The involved contents are the realization of various Si- based optoelectronic devices, such as light- emitting diodes, optical waveguides devices, Si photonic bandgap crystals, and Si laser,etc. Finally, the developed tendency of all-Si optoelectronic integrated technology are predicted in the near future.     

Effect of temperature on the intensity and carrier lifetime of an AlGaAs based red light emitting diode

The influence of temperature on the intensity of light emitted by as well as the carrier life time of a standard AlGaAs based light emitting diode has been investigated in the temperature range from 345 to 136 K. The open-circuit voltage decay(OCVD) technique has been used for measured the carrier lifetime. Our experimental results reveal a 16% average increase in intensity and a 163.482-19.765 ns variation in carrier lifetime in the above temperature range. Further, theoretical and experimental analysis show that for negligible carrier density the intensity is inversely proportional to carrier lifetime for this sample.     

High Speed VCSEL-Based Parallel Optical Transmission Modules

Design and fabrication of a parallel optical transmitter are reported.The optimized 12 channel parallel optical transmitter,with each channel’s data rate up to 3Gbit/s,is designed,assembled,and measured.A topemitting 850nm vertical cavity surface emitting laser(VCSEL) array is adopted as the light source,and the VCSEL chip is directly wire bonded to a 12 channel driver IC.The outputs of the VCSEL array are directly butt coupled into a 12 channel fiber array.Small form factor pluggable (SFP) packaging technology is used in the module to support hot pluggable in application.The performance results of the module are demonstrated.At an operating current of 8mA,an eye diagram at 3Gbit/s is achieved with an optical output of more than 1mW.     

Development of a fiber optic health monitoring system for aerospace applications

This paper describes our research activity involved in the identification, development and test of a prototype SHM system constituted by optical sensing nodes to measure both temperature and strain on ultra high temperature ceramics (UHTC) materials up to 1000 °C. Commercially available optic devices can operate up to 550 °C. To raise temperature limit up to 1000 °C, custom devices, mainly under development for scientific applications, have been identified. A prototype SHM system has been developed adopting a FBG sensor for temperature measurement and an EFPI sensor in sapphire fiber for strain measurement. The preliminary findings from thermo-mechanical tests indicate that former SHM system is capable of accurately measuring strain at elevated temperatures on UHTC materials.     

Temperature dependences of electroluminescent characteristics inthe devices fabricated with novel triphenylamine derivatives

In this paper, we investigated the temperature dependences of the electroluminescent (EL) characteristics of two-layer devices fabricated using four hole-transporting materials based on triphenylamine, and a typical emitting material, tris (8-quinolinolato) aluminum. The thermal stability of the organic EL devices is clearly seen to depend on the glass transition temperature (T_g) of the hole-transporting material. The EL device with a pentamer of triphenylamine exhibits uniform light emission in a continuous operation up to 155°C without breakdown. A lowering of the “turn-on voltage” for light emission and an increase of luminous efficiency with increasing temperature are found in the devices. Excellent durability of continuous operation is also achieved at high temperatures. Our results indicate that the linear linkage of triphenylamine provides the high T_g material and the high device performance at high temperatures     

Efficient silicon based light emitters

Recent progress on electrically driven silicon based light emitters is reviewed, with emphasis on our work on light emitting pn diodes (LED) and MOS devices doped with rare-earth elements. The LEDs were fabricated by high-dose boron implantation, producing nanoscale modifications in the material. The electroluminescence (EL) efficiency increases with temperature, reaching 0.1% (wall plug efficiency) at room temperature for optimized conditions. Such devices were integrated into a microcavity. In the MOS devices, the oxide was implanted with various rare-earth elements, resulting in strong EL in the visible (Tb) and ultraviolet (Gd). External quantum efficiencies in excess of 10% are reported.     

Nanoimprinting lithography on 200 mm wafers for optical applications

This paper presents how nanoimprint lithography is developed on 200 mm wafers for the fabrication of two optical devices: parts for optical encoders and organic light emitting diodes with enhanced light extraction efficiency. The optimization of the printing process is shown for both applications. Special studies are presented on the development of etching processes. The removing of the residual layer still needs efforts to guarantee the fidelity of the final patterns but we demonstrated that specific plasma chemistry leads to a high control of the pattern size during this etching step. It is even proved that an over-etch can be performed with no change of the structure dimensions. Final structures duplicated in Si or SiO₂ are then presented.     

Visible electroluminescence from stain-etched porous Si diodes

Visible electroluminescence (EL) from stain-etched porous silicon (PoSi) films is presented. The PoSi thin layers (~200 nm) were obtained by stain-etching of B-doped 6-16 Ω-cm (100) crystalline Si in a HF:HNO₃:H₂O (1:3:5) solution. Indium tin oxide (ITO) films of ~2500 Å were used to form a Schottky contact. Visible EL was observed at room temperature from the diode under forward bias. EL onset bias as low as 3 mA/cm² was measured. The EL, with an emission peak at ~640 nm, is similar to the photoluminescence under UV excitation, indicating the same luminescent centers. This result demonstrates a promising and simple technique for the fabrication of PoSi-based light emitting diodes and flat panel display devices     

From White to Red: Electric‐Field Dependent Chromaticity of Light‐Emitting Electrochemical Cells based on Archetypal Porphyrins

The differences in the electroluminescence (EL) of red‐emitting free‐base ( H2TPP ) and Zn‐metalated ( ZnTPP ) archetypal porphyrins are rationalized in light‐emitting electrochemical cells by means of an electric‐field dependent effect, leading to whitish and reddish devices, respectively. Although H2TPP shows superior electrochemical and photophysical features compared to ZnTPP , devices prepared with ZnTPP surprisingly stand out with a deep‐red EL similar to its photoluminescence (PL), while H2TPP devices feature unexpected whitish EL. Standard arguments such as degradation, device architecture, device mechanism, and changes in the nature of the emitting excited states are discarded. Based on electrochemical impedance spectroscopy and first‐principles electronic structure methods, we provide evidence that the EL originates from two H2TPP regioisomers, in which the inner ring H atoms are placed in collinear and vicinal configurations. The combination of their optical features provides an explanation for both the high‐ and low‐energy EL features. Here, the emitting excited state nature is ascribed to the Q bands, since the Soret excited states remain high in energy. This contrasts to what is traditionally postulated in reports focused on H2TPP lighting devices. Hence, this work provides a new explanation for the nature of the high‐energy EL band of H2TPP that might inspire future works focused on white‐emitting molecular‐based devices.     

Characterization of indium tin oxide surfaces after KOH and HCl treatments

The extraction of the light produced by an organic light emitting diode has been made possible by the use of transparent conductive materials which should have well defined electronic and optical properties. All the requirements are satisfied by indium tin oxide which has rapidly become the most common conductive substrate used for the growth of organic light emitting sources. Atomic force microscope, conventional X-ray photoemission spectroscopy and scanning photoemission spectromicroscopy have been used to investigate the morphology and the chemical properties of commercial thin indium tin oxide films after several treatments commonly used prior to the organic layer growth for smoothing/cleaning/patterning the surface. Unambiguous smoothing effects of the potassium hydroxide-based solutions have not been observed while Si contaminations of the surfaces have been found after the application of different patterning procedures.     

Some silicon-based heterostructures for optical applications

In this paper, we will present our recent research on the growth and characterization of some Si-based heterostructures for optical and photonic devices. The heterostructures to be discussed are ZnO nanorods on Si, SiO₂, and other substrates such as SiN and sapphire. We will also consider strained Si_1−xGe_x/Si heterostructures for Si optoelectronics. The performance and functionality extension of Si technology for photonic applications due to the development of such heterostructures will be presented. We will focus on the results of structural and optical characterization in relation to device properties. The structural characterization includes x-ray diffraction for assessment of the crystallinity and stress in the films and secondary ion mass spectrometry for chemical analysis. The optical properties and electronic structure were investigated by using photoluminescence. The device application of these thin film structures includes detectors, lasers, and light emitting devices. Some of the Si-based heterostructures to be presented include devices emitting and detecting up to the blue-green and violet wave lengths.     

Light Extraction Efficiency Enhancement of Colloidal Quantum Dot Light‐Emitting Diodes Using Large‐Scale Nanopillar Arrays

A colloidal quantum dot light‐emitting diode (QLED) is reported with substantially enhanced light extraction efficiency by applying a layer of large‐scale, low‐cost, periodic nanopillar arrays. Zinc oxide nanopillars are grown on the glass surface of the substrate using a simple, efficient method of non‐wetting templates. With the layer of ZnO nanopillar array as an optical outcoupling medium, a record high current efficiency (CE) of 26.6 cd/A is achieved for QLEDs. Consequently, the corresponding external quantum efficiency (EQE) of 9.34% reaches the highest EQE value for green‐emitting QLEDs. Also, the underlying physical mechanisms enabling the enhanced light‐extraction are investigated, which leads to an excellent agreement of the numerical results based on the mode theory with the experimental measurements. This study is the first account for QLEDs offering detailed insight into the light extraction efficiency enhancement of QLED devices. The method demonstrated here is intended to be useful not only for opening up a ubiquitous strategy for designing high‐performance QLEDs but also with respect to fundamental research on the light extraction in QLEDs.     

Gaq3有机薄膜电致发光器件

首次报道了采用８－羟基喹啉镓螯合物作为发光层制备有机薄膜电致发光器件，器件的结构为：ＩＴＯ导电玻璃／ＴＰＤ／Ｇａｑ３／Ａｌ。研究了Ｇａｑ３薄膜的光致发光和器件的电致发光机理，同时测量和研究了器件的电流密度－－电压（Ｊ－Ｖ）特性和发光亮度－电压（Ｂ－Ｖ）特性。结果表明器件的电致发光峰值波长为５４０ｎｍ，在２０Ｖ直流电压驱动下的最大发光亮度约２５００ｃｄ／ｍ＾２明显高于上同结构和工艺参数制备的Ａｌｑ３     

Indium Tin Oxide Thin Films Grown on Polyethersulphone (PES) Substrates by Pulsed‐Laser Deposition for Use in Organic Light‐Emitting Diodes

High quality indium tin oxide (ITO) thin films were grown by pulse laser deposition (PLD) on flexible polyethersulphone (PES) substrates. The electrical, optical, and surface morphological properties of these films were examined as a function of substrate temperature and oxygen pressure. ITO thin films, deposited by PLD on a PES substrate at room temperature and an oxygen pressure of 15 mTorr, have a low electrical resistivity of 2.9×10^?4 Ω cm and a high optical transmittance of 84 % in the visible range. They were used as the anode in organic light‐emitting diodes (OLEDs). The maximum electro luminescence (EL) and current density at 100 cd/m² were 2500 cd/m² and 2 mA/cm², respectively, and the external quantum efficiency of the OLEDs was found to be 2.0 %.