表面粗化对GaN基垂直结构LED出光效率的影响

用加热后的KOH水溶液腐蚀GaN材料的N极性面,用以提高GaN基垂直结构发光二极管(LED)的出光效率。经过湿法腐蚀后,构成N极性面的表面晶粒尺寸和密度成为影响垂直结构LED提取效率的主要因素,通过分析不同腐蚀条件下晶粒尺寸和密度与出光效率间的关系,得到最优化的粗化条件,使得器件的提取效率达到最佳。经由浓度为30%、温度为60℃的KOH溶液腐蚀后,未封装的垂直结构LED芯片的提取效率增加了近1倍。     

GaAs—GaAlAs双异质结发光管的欧姆接触

一、前言欧姆接触是制管工艺的主要环节之一,欧姆接触的好坏对器件性能有很大的影响。为了使所需的电压电流顺利地加到发光器件上,发光二极管必须具有N面和P面电极。电极和器件之间应形成良好的欧姆接触。良好的欧姆接触应具备下列条件:(一)具有低的接触电阻;(二) 电极材料不宜过深掺入半导体内,由于制作接触电极而引起的半导体结构上的变化不致于引起器件其他特性的变化;(三) 电极和半导体接触面必     

一种具有鳍状阳极的垂直GaN功率二极管

针对垂直GaN肖特基二极管击穿电压低、泄漏电流大等问题,提出了一种具有鳍状(Fin)阳极结构的高压垂直GaN功率二极管。该结构利用阳极金属与GaN半导体之间的功函数差耗尽二极管阳极与阴极之间的导电沟道,实现二极管关断及反向耐压的功能,因此,阳极不再需要进行肖特基接触,仅需欧姆接触即可。通过优化Fin阳极结构参数,新结构同时实现高击穿电压和低正向导通压降,该器件的击穿电压为1 791 V(@ 1×10-4 A/cm²),正向导通压降为0.815 V(@ 100 A/cm²),导通电阻仅为0.73 mΩ·cm²且具有高的温度稳定性,开态电流摆幅高达1×10¹²量级。     

长波长VCSEL结构中的欧姆接触工艺

简要叙述了欧姆接触工艺在长波长垂直腔面发射激光器(VCSEL)制作中的重要作用.采用圆环传输线方法(CTLM)研究了应用于长波长VCSEL结构的p型InGaAsP和InP材料与Ti-Au的接触特性,发现p-InGaAsP与Ti-Au经高温退火后能获得欧姆接触,其最低比接触电阻值可达6.49×10-5Ω·cm2.将此工艺结果应用于1.3 μm VCSEL结构中,发现其开启电压和串联电阻显著减小.     

关于提高高亮度发光二极管发光效率的探讨

使用高亮度发光二极管(HB-LED)的半导体照明技术正受到全球关注,而存在的主要问题是发光效率低。本文指出发光效率即外量子效率是内量子效率和提取效率的乘积。提高内量子效率的方法是获得高质量GaN材料的外延技术,采用四组分AlInGaN结构及在半极性面或非极性面上制作LED,提高提取效率的途径主要有倒装焊技术、表面粗化技术、芯片粘合技术、芯片成形技术以及微芯片阵列技术等。     

势垒材料对GaN基异质结电学特性的影响研究

基于势垒材料分别为Al0.27Ga0.73N和In0.17Al0.83N的GaN基异质结肖特基二极管(SBD),研究了GaN基异质结的漏电流输运机制、二维电子气密度和反向击穿电压等重要电学特性。结果表明,AlGaN/GaN SBD的反向电流主要由Frenkel-Poole(FP)发射机制主导,而InAlN/GaN SBD的反向电流在低电场下表现为FP发射电流,在高电场下则表现为Fowler-Nordheim隧穿电流。InAlN/GaN SBD的异质界面二维电子气密度明显高于AlGaN/GaN SBD,但是InAlN层存在高密度的缺陷,导致InAlN/GaN SBD的反向漏电流较大,且反向击穿电压较低。     

p型InGaN/GaN超晶格N面GaN基LED的光电特性

随着氮(N)面GaN材料生长技术的发展,基于N面GaN衬底的高亮度发光二极管(LED)的研究具有重要的科学意义.研究了具有高发光功率的N面GaN基蓝光LED的新型结构设计,通过在N面LED的电子阻挡层和多量子阱有源层之间插入p型InGaN/GaN超晶格来提高有源层中的载流子注入效率.为了对比N面GaN基LED优异的器件性能,同时设计了具有相同结构的Ga面LED.通过对两种LED结构的电致发光特性、有源层中能带图、电场和载流子浓度分布进行比较可以发现,N面LED在输出功率和载流子注入效率上比Ga面LED有明显的提升,从而表明N面GaN基LED具有潜在的应用前景.     

4H-SiC结型势垒肖特基二极管的制作与特性研究

本文设计制作了两种具有不同结构参数的4H-SiC结型势垒肖特基二极管,在制作过程中采用了两种制作方法：一种是对正电极上的P型欧姆接触进行单独制作,然后制作肖特基接触的工艺过程;另一种是通用的通过一次肖特基接触制作就完成正电极制作的工艺过程。器件制作完成后,通过测试结果比较了采用场限环作为边界终端与未采用边界终端的器件的反向特性,结果显示采用场限环有效地提高了该器件的击穿电压,减小了其反向电流。另外,测试结果还显示采用独立制作P型欧姆接触的工艺过程有效提高了4H-SiC结型势垒肖特基二极管的反向特性,其中P型欧姆接触的制作过程和结果也在本文中做出了详细叙述。     

n型GaN欧姆接触的研究进展

Ⅲ-Ⅴ族GaN基材料以其在紫外光子探测器、发光二极管、高温及大功率电子器件等方面的应用潜能而被广为研究.其中,低阻欧姆接触是提高GaN基器件光电性能的关键.金属/GaN界面上较大的欧姆接触电阻一直是影响器件性能及可靠性的一个问题.对于各种应用来说, GaN的欧姆接触需要得到改进.通过对相关文献的归纳分析,本文主要介绍了近年来在改进n-GaN工艺,提高欧姆接触性能等方面的研究进展.     

P型GaN器件欧姆接触的研究进展

Ⅲ-Ⅴ族GaN基材料以其在紫外光子探测器、发光二极管、高温及大功率电子器件方面的应用潜能而被广为研究.低阻欧姆接触是提高GaN基器件光电性能的关键.由于低掺杂和空穴电离等原因,p-GaN上的低阻接触难于制备.制备稳定的P-GaN欧姆接触一直是一个挑战.主要通过对有关英语期刊文献的归纳分析,介绍了近年来在改进P-GaN工艺、提高欧姆接触性能等方面的研究进展.     

Electrical characteristics of a vertical light emitting diode with n-type contacts on a selectively wet-etching roughened surface

Low resistance and thermally stable n-type contacts to N-polar GaN are essentially important for vertical light emitting diodes(VLEDs).The electrical characteristics of VLEDs with n-type contacts on a roughened and flat N-polar surface have been compared.VLEDs with contacts deposited on a roughened surface exhibit lower leakage currents yet a higher operating voltage.Based on this,a new scheme by depositing metallization contacts on a selectively wet-etching roughened surface has been developed.Excellent electrical and optical characteristics have been achieved with this method.An aging test further confirmed its stability.     

Electrical Characteristics of Metal Contacts to Laser-Irradiated N-Polar n-Type GaN

Electrical characteristics of metal contacts to a laser-irradiated thin-film N-polar n-type GaN surface are investigated. It is shown that the laser irradiation of the N-polar n-GaN results in a significant increase (as high as $hbox{3.0} times hbox{10}^{20} hbox{cm}^{-3}$) in the electron concentration and a decrease in the Schottky barrier height by 0.05 eV (0.28 eV), as estimated using Pt-based Schottky diodes (X-ray photoemission spectroscopy). Ti/Al contacts to the laser-irradiated N-polar sample exhibit an excellent Ohmic behavior with thermal stability up to 600 $^{circ} hbox{C}$, indicating that the laser irradiation treatment can be a very promising technology in practical applications.      

Further Enhancement of Nitride-Based Near-Ultraviolet Vertical-Injection Light-Emitting Diodes by Adopting a Roughened Mesh-Surface

In this letter, the nitride-based near-ultraviolet (NUV) vertical-injection light-emitting diodes (VLEDs) with roughened mesh-surface are proposed and demonstrated by a combination of pattern sapphire substrate, wafer bonding, laser lift-off, and chemical wet etching processes. With the help of adopting a roughened mesh-surface, the light-output power (at 350 mA) of the NUV-VLEDs could be further enhanced about 20% as compared with that of the conventional NUV-VLED.     

Improving performance of high-power indium gallium nitride/gallium nitride-based vertical light-emitting diodes by employing simple n-type electrode pattern

In this work, simple n-type electrode structures were used to enhance the electrical and optical performances of fully packaged commercially mass-produced vertical-geometry light-emitting diodes (VLEDs). The forward bias voltage of the VLED with a Y-pattern electrode increased less rapidly than that of VLEDs with a reference electrode. The VLEDs with the reference and Y-pattern electrodes exhibited forward voltages of 2.93±0.015 and 2.89±0.015 V at 350 mA and 3.77±0.015 and 3.53±0.015 V at 2000 mA, respectively. The VLEDs with the Y-pattern electrode resulted in a higher light output than the VLEDs with the reference electrode with increase in the drive current to 2000 mA. The emission images showed that the VLEDs with the Y-pattern electrode exhibited better current spreading behavior and lower junction temperatures than the VLEDs with the reference electrode. With increase in the current from 350 to 2000 mA, the VLEDs with the Y-pattern electrode experienced a 39.4% reduction in the wall plug efficiency, whereas the VLEDs with the reference electrode suffered from a 43.3% reduction.     

Electrical properties of metal-diamond-like-nanocomposite (Me-DLN) contacts to 6H SiC

We have fabricated tungsten-diamond-like-nanocomposite (W-DLN) Schottky contacts on n-type and p-type 6H SiC (Si-face). The as-deposited n-type and p-type contacts are rectifying and measurement results suggest that the electrical characteristics are dominated by the properties of the tungsten SiC interface. The n-type contacts have a reverse leakage current density of 4.1 × 10⁻³ Acm⁻² and the p-type contacts have a reverse leakage current density of 1.4 × 10⁻⁷ Acm⁻² at −10 V. The n-type contacts have an current-voltage (I-V) extracted effective ϕ_Bn of 0.7 eV with an ideality factor of 1.2 and a capacitance-voltage (C-V) extracted ϕ_Bn of 1.2 e V. The p-type contacts have an I-V extracted effective ϕ_Bp of 1.8 eV with an ideality factor of 1.7. Non-ideal I-V and C-V characteristics may be due to surface damage during W-DLN deposition.     

Enhanced Light Output Power of GaN-Based Vertical Light-Emitting Diodes by Using Highly Reflective ITO–Ag–Pt Reflectors

Highly reflective and thermally stable indium–tin–oxide (ITO)–Ag–Pt p-type reflectors for use in high-performance GaN-based light-emitting diodes (LEDs) have been investigated. The specific contact resistance of the ITO–Ag–Pt contacts was found to be $7.2 times 10 ^{-5} Omegacdothbox{cm}^{2}$ . The ITO–Ag–Pt contacts showed a higher reflectance after thermal annealing (82% at 460 nm), while the reflectance of the ITO–Ag contacts was reduced from 81% to 65%. In addition, surface agglomeration was drastically decreased, indicating that the Pt layer efficiently prevents the surface agglomeration of the Ag layer. The vertical LEDs (VLEDs) fabricated with the ITO–Ag–Pt contacts had a 17% higher output power (at 20 mA) than the VLEDs fabricated with the ITO–Ag contacts.      

Fabrication and characterization of nonalloyed Cr/Au ohmic contacts to n- and p-type In0.53Ga0.47As

Ion implantation and rapid thermal annealing have been used to selectively produce thin high carrier concentration n- and p-type layers on In0.53Ga0.47As, and nonalloyed ohmic contacts with excellent properties have been achieved by depositing layers of Cr and Au on the implanted regions. The Cr/Au metallization is used to produce ohmic contacts on both p-type and n-type material in the same deposition. A series of electrical test patterns based on the transmission line model and four terminal structure were used to characterize the contact resistance of both alloyed and nonalloyed ohmic contact metallizations on In0.53Ga0.47As. The nonalloyed contacts to n-type material are superior to conventional alloyed contacts made in this study, while the nonalloyed contacts to p-type material are a factor of 5 higher resistance.     

AuGe/Au ohmic contacts to n-type InP by hot-plate alloying

The authors report on the fabrication and characteristics of AuGe/Au ohmic contacts to ion-implanted n-type InP. The contacts have smooth surface morphology, excellent adhesion and good contact resistance uniformity. For samples with carrier concentrations of 1.7 * 10/sup 17/ and 1.6 * 10/sup 18/ cm/sup -3/, contact resistances of 0.07 and 0.03 Omega mm, respectively, have been obtained. These values are among the lowest contact resistances reported for n-type InP.<>     

Enhanced Light Output in Roughened GaN-Based Light-Emitting Diodes Using Electrodeless Photoelectrochemical Etching

We have demonstrated enhanced output power from roughened GaN-based light-emitting diodes (LEDs) by using electrodeless photoelectrochemical etching with a chopped source (ELPEC-CS etching). It was found that the 20-mA output power of the ELPEC-CS treated LED (with roughened surfaces on the top p-type and bottom n-type GaN surface as well as the mesa sidewall) was 1.41 and 2.57 times as high as those LEDs with a roughened p-type GaN surface and a conventional surface, respectively. The light output pattern of the ELPEC-CS treated LED was five times greater than the conventional LED at 0deg which was caused by the roughened GaN surface that improved the light extraction efficiency of the LED     

High efficiency submilliamp vertical cavity lasers with intracavitycontacts

Contacts have been made to p- and n-type layers on opposite sides of the active region within the cavity of an InGaAs vertical cavity surface emitting laser. The two concentric ring contacts allow all electrical connections on and emission from the top surface of a semi-insulating GaAs substrate. The design includes a novel current leveling layer to minimize current crowding effects. A high external quantum efficiency of 46% has been measured with maximum output powers up to 6 mW for a 15 μm diameter device and threshold currents of 0.72 mA for a 7 μm diameter laser