ZnMgO/n-ZnO/ZnMgO/p-GaN异质结LED的紫外电致发光

利用等离子体辅助分子束外延( P-MBE)技术制备了ZnMgO/n-ZnO/ZnMgO/p-GaN异质结LED.Ni/Au电极与p-GaN、In电极与ZnMgO之间都形成了良好的欧姆接触.在ZnMgO/n-ZnO/ZnMgO/p-GaN异质结器件中观察到了明显的整流特性.异质结的电致发光强度随着注入电流的增大而逐渐增强...     

n-ZnO/i-MgO/p-GaN异质结发光二极管

用等离子体辅助分子束外延的方法生长了n-ZnO/i-MgO/p-GaN异质结发光二极管。I-V测量表明其具有典型的二极管整流特性。电致发光峰位于382nm,通过与n型ZnO和p型GaN的光致发光谱比较,其发光峰位与线形都与ZnO的自由激子发射一致,表明该电致发光来自于ZnO的自由激子发射。通过Anderson模型比较了n-ZnO/i-MgO/p-GaN和n-ZnO/p-GaN异质结的能带示意图,证明了由于MgO层的插入抑制了ZnO向GaN层中的电子注入,且有利于空穴向ZnO层注入,从而实现了ZnO层中的电注入发光。     

Electroluminescence from ZnO nanowire-based p-GaN/n-ZnO heterojunction light-emitting diodes

Vertically aligned ZnO nanowires were successfully grown on the sapphire substrate by nanoparticle-assisted pulsed laser deposition (NAPLD), which were employed in fabricating the ZnO nanowire-based heterojunction structures. p-GaN/n-ZnO heterojunction light-emitting diodes (LEDs) with embedded ZnO nanowires were obtained by fabricating p-GaN:Mg film/ZnO nanowire/n-ZnO film structures. The current–voltage measurements showed a typical diode characteristic with a threshold voltage of about 2.5 V. Electroluminescence (EL) emission having the wavelength of about 380 nm was observed under forward bias in the heterojunction diodes and was intensified by increasing the applied voltage up to 30 V.     

Influence of growth temperature and post-annealing on an n-ZnO/p-GaN heterojunction diode

We report on an n-ZnO/p-GaN heterojunction diode fabricated from zinc oxide (ZnO) films at various growth temperatures (450, 500, 550, and 600 °C) by RF sputtering. The films were subsequently annealed at 700 °C in N₂ ambient. To investigate the influence of the growth temperature of n-ZnO films, the microstructural, optical, and electrical properties were measured using scanning electron microscopy (SEM), X-ray diffraction (XRD), photoluminescence (PL), and Hall measurements. The XRD pattern showed the preferred orientation along the c-axis (002) regardless of growth temperature. The PL spectra showed a dominant sharp near-band-edge (NBE) emission. Current–voltage (I–V) curves showed excellent rectification behavior. The turn-on voltage of the diode was observed to be 3.2 V for the films produced at 500 °C. The ideality factor of ZnO film was observed to be 1.37, which showed the best performance of the diode.     

反向驱动的异质结有机薄膜电致发光

成功制备了结构为ITO／PDDOPV／PPQ／Al的异质结聚合物发光二极管。该器件在正反向偏压下均可发光。在正向偏压下的光发射主要来自PDDOPV，但在反向偏压下的光发射则包括来自PPQ的蓝光发射和PDDOPV的黄光发射。蓝光强度与黄光强度的比值随着反向偏压的增加而增加，当反向直流电压分别为22V、24V、26V、28V时，其电致发光光谱中PPQ与PDDOPV的峰高比IPPQ／IPDDOPV分别为1．092、1．329、1．605、2．046。换句话说，该器件的发光颜色是压控可调的，这对实现彩色显示是极为有利的。分析了在反向偏压下的发光机理以及IPPQ／IPDDOPV受电压控制的原因。     

The influence of ZnO seed layers on n-ZnO nanostructure/p-GaN LEDs

Light-emitting diodes (LEDs) were formed by hydrothermally growing n-ZnO nanostructures on p-GaN with or without seed layers. The performance of the fabricated LEDs was studied. The seed layers not only have a great influence on the morphology and density of the ZnO nanostructures but also determine the lighting bias and emitting mechanism. The LEDs without seed layers and with sputtered seed layers exhibit light emission only under reverse bias, which is believed due to the GaN buffer layer/p-GaN p–n junction. The LEDs with sol–gel seed layers exhibit light emission under both forward and reverse biases. With the increase of the forward bias, the LEDs first demonstrate a red electroluminescence emission coming from the sol–gel seed layers and then demonstrate an orange emission coming from the ZnO nanorods. The sol–gel seed layer and the interface play a very important role in the electroluminescence.     

A new approach to white light emitting diodes of p-GaN/i-ZnO/n-ZnO heterojunctions

A simple method to fabricate one-chip white light emitting diodes (LEDs) is proposed. A series of p-GaN/i-ZnO/n-ZnO heterojunctions fabricated by pulsed laser deposition exhibit simultaneous Mg-related p-GaN (blue-violet) and deep-level i-ZnO (yellow) emissions under forward bias. Current–voltage measurements show a typical rectifying characteristic. Yellow emission intensity, and consequently the ratio of yellow to blue-violet emission, are tunable through control of the i-ZnO layer thickness. Heterojunctions with a 20 nm-thick i-ZnO layer exhibit white electroluminescence. PACS  78.60.Fi; 73.40.Lq; 85.60.Jb     

ZnO纳米棒／MEH-PPV异质结的复合电致隧穿发光

利用低温水热法生长的ZnO纳米棒（ZnO-NRs）,和p型有机半导体材料聚[2-甲氧基-5-（2-乙基己氧基）-1,4-苯撑乙烯撑]（MEH-PPV）复合制备了结构为“ITO/ZnO晶种/ZnO-NRs/MEH-PPV/Al”的发光器件。测试结果发现,该器件具有非常好的二极管整流特性。对ZnO-NRs/M EH-PPV异质结施加超过17 V的反向偏压时,可同时获得两种半导体材料的发光,且ZnO近紫外光（380 nm ）发射强度远大于 M EH-PPV的红橙光强度,发光功率随着反向偏压的增加迅速增强,然而施加正向偏压时未探测到发光。该器件的发光机理不同于其他文献报道的正偏压发光,而属于反偏压发光器件,其发光机理归因于有机无机复合异质结的界面特殊性和ZnO-NRs的纳米尺寸效应,反偏压下器件实现的是载流子隧穿发光,而正偏压时载流子以表面态的无辐射复合及漏电流方式消耗。     

Electroluminescence from ZnO nanowires with a p-ZnO film/n-ZnO nanowire homojunction

ZnO homojunction light-emitting diodes based on ZnO nanowires were fabricated on Si(100) substrates. An N–In codoped p-type ZnO film grown by ultrasonic spray pyrolysis and an unintentionally doped n-type ZnO nanowire quasi-array grown by an easy low-temperature hydrothermal method were employed to form the homojunction diode. Under a forward bias larger than 8 V, electroluminescence, which was composed of an ultraviolet peak centered at 387 nm and a green band around 540 nm, was observed. The electroluminescence emission was contributed by the ZnO nanowires. The results reported here suggest that ZnO-based ultraviolet light-emitting devices could be realized at low cost. PACS 42.72.Bj; 73.40.Lq; 85.60.Jb     

Improvement in electroluminescence performance of n-ZnO/Ga_2O_3 /p-GaN heterojunction light-emitting diodes

n-ZnO/p-GaN heterojunction light-emitting diodes with and without a Ga2O3 interlayer are fabricated. The electroluminescence （EL） spectrum of the n-ZnO/p-GaN displays a single blue emission at 430 nm originating from GaN, while the n-ZnO/Ga2O3/p-GaN exhibits a broad emission peak from ultraviolet to visible. The broadened EL spectra of n-ZnO/Ga2O3/p-GaN are probably ascribed to the radiative recombination in both the p-GaN and n-ZnO, due to the larger electron barrier （ΔEC=1.85 eV） at n-ZnO/Ga2O3 interface and the much smaller hole barrier （ΔEV=0.20 eV） at Ga2O3/p-GaN interface.     

Low-voltage blue light emission from n-ZnO/p-GaN heterojunction formed by RF magnetron sputtering method

High quality n-ZnO/p-GaN heterojunction was fabricated by growing highly crystalline ZnO epitaxial films on commercial p-type GaN substrates via radio frequency (RF) magnetron sputtering. Low-voltage blue light emitting diode with a turn-on voltage of ∼2.5 V from the n-ZnO/p-GaN heterojunction was demonstrated. The diode gives a bright blue light emission located at ∼460 nm and a low threshold voltage of 2.7 V for emission. Based on the results of the photoluminescence (PL) and electroluminescence (EL) spectra, the origins of the EL emissions were studied in the light of energy band diagrams of ZnO–GaN heterojunction, and may attribute to the radiative recombination of the holes in p-GaN and the electrons injected from n-ZnO, which almost happened on the side of p-GaN layer. These results may have important implications for developing short wavelength optoelectronic devices.     

Electroluminescence of the p-ZnO:As/n-ZnO LEDs grown on ITO glass coated with GaAs interlayer

In this paper, we proposed a new p-type ZnO doping method with metal organic chemical vapor deposition (MOCVD) technology by inserting a GaAs interlayer between substrate and ZnO epitaxial layer. The doping concentration of p-type ZnO film is able to be controlled by adjusting the thickness of the GaAs interlayer. With this method, we fabricated n-ZnO/p-ZnO:As homojunction light-emitting diode (LED) on ITO-glass substrate pre-coated with 20 nm GaAs interlayer. The device exhibits a typical rectifying behavior by current-voltage (I-V) measurement. When the device is forward biased, UV-vis electroluminescence (EL) emissions can be observed clearly.     

Photovoltaic and Electroluminescence Characters in Hybrid ZnO and Conjugated Polymer Bulk Heterojunction Devices

We report electroluminescence in hybrid ZnO and conjugated polymer poly[2-methoxy-5-（3′, 7′-dimethyloctyloxy）- 1,4-phenylenevinylene] （MDMO-PPV） bulk heterojunction photovoltaic cells. Photoluminescence quenching experimental results indicate that the ultrafast photoinduced electron transfer occurs from MDMO-PPV to ZnO under illumination. The ultrafast photoinduced electron transfer effect is induced because ZnO has an electron affinity a bout 1.2 e V greater than that of MDMO-PP V. Electron ＇back transfer＇ can occur if the interfacial barrier between ZnO and MDMO-PPV can be overcome by applying a substantial electric field. Therefore, electrolumi- nescence action due to the fact that the back transfer effect can be observed in the ZnO：MDMO-PPV devices since a forward bias is applied. The photovoltaic and electroluminescence actions in the same ZnO：MDMO-PPV device can be induced by different injection ways： photoinjection and electrical injection. The devices are expected to provide an opportunity for dual functionality devices with photovoltaic effect and electroluminescence character.     

Electroluminescence of the electrolyte/n-ZnSe junction under anodic polarization

The electroluminescent properties of the electrolyte/ZnSe junction give important information on electron transfer across the interface. Adsorption of OH^? groups on it, that enables electron injection into the semiconductor, accounts for a luminescence at 2.0 eV, produced by an impact-ionization mechanism already observed in solid state diodes. Addition of Cu²⁺ ions in the electrolyte gives an additional luminescene at an energy of 2.2 eV. This phenomenon is connected to the adsorption of Cu⁰ and Cu²⁺ onto the semiconductor surface in relation with a corresponding energy level Cu^X_Zn in the semiconductor bulk.     

Green electroluminescence from an n-ZnO: Er/p-Si heterostructured light-emitting diode

Erbium-doped ZnO (ZnO:Er) thin films with various doping concentrations were deposited on p-Si substrates by ultrasonic spray pyrolysis (USP). The n-ZnO:Er/p-Si heterojunctions were further employed to fabricate light-emitting diodes (LEDs). The devices showed diode-like rectifying current–voltage characteristics with a low reverse breakdown voltage, attributed to the avalanche breakdown. A distinct green electroluminescence peaking at 537 nm and 558 nm were observed at room temperature under reverse bias. The green electroluminescence originated from the electron impact excitation of Er³⁺ ions doped in ZnO films.     

有机吡啶盐的电致发光

有机盐是一种离子化合物,其分子间依靠比范德瓦尔斯力大得多的离子键结合,这有利于器件稳定性的提高。主要研究一种以新型有机吡啶盐ASPT(trans-4-[P-(N-ethyl-N-(hydroxylethyl)-amino)styryl]-N-methylpyridinium tetraphenyl-borate)作发光层的有机电致发光特性。实验发现有机盐ASPT是一种性能较好的红光发射材料。利用ASPT作发光层的单层电致发光器件,可获得稳定的红色电致发光。通过对外场界面势垒影响分析,我们讨论了这种单层器件的发光机理。为了探索ASPT中载流子传输与复合过程,并提高器件性能,设计了ASPT/Alq₃双层和TPD/ASPT/Alq₃三层结构的器件,进一步研究了它们的光电特性。实验结果表明,利用双层器件可获得亮度较高的红色发光。而在三层器件中,由于不同功能层的载流子传输特性的差别,激发复合区域受到驱动电压的显著影响,因此电致发光光谱随电压的变化而变化。通过对光谱结构、能级位置的分析,讨论了相关的发光机理。     

Electroluminescence of an ITO-n-CdTe SIS structure

An ITO-n-CdTe electroluminescence structure of the semiconductor-insulatorsemiconductor type has been studied. Under forward bias hole injection from the ITO into the n-CdTe base material causes electroluminescence with its wavelength at the maximum (0.87 m) of the spectral distribution of the luminescence. The injection coefficient and the transparency of the insulator layer are determined for both types of carriers.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 38–41, March, 1989.     

The effect of a surface layer capping p-InGaN/p-GaN superlattices on the contact to p-GaN

In this study, the influence of the surface layer (p-InGaN or p-GaN) capping p-InGaN/p-GaN superlattices (SLs) on the contact to p-type GaN was investigated. It was found that the specific contact resistance (_ρc)$\left({\rho }_c\right)$ to p-type GaN is lower when using p-InGaN as the surface layer. The lowest value of _ρc${\rho }_c$ was 1.99×10⁻⁴ Ω cm² at room temperature. It was also found that low temperature growth of the p-GaN layers in the SLs is beneficial for lowering the ohmic contact resistance. Unlike Ni/Au deposited directly on p-GaN (without the strained p-InGaN/p-GaN SLs), Ni/Au deposited on p-InGaN/p-GaN SLs produces ohmic behavior even before annealing.     

Low contact resistivity between Ni/Au and p-GaN through thin heavily Mg-doped p-GaN and p-InGaN compound contact layer

Thin heavily Mg-doped In Ga N and Ga N compound contact layer is used to form Ni/Au Ohmic contact to p-Ga N.The growth conditions of the compound contact layer and its effect on the performance of Ni/Au Ohmic contact to p-Ga N are investigated. It is confirmed that the specific contact resistivity can be lowered nearly two orders by optimizing the growth conditions of compound contact layer. When the flow rate ratio between Mg and Ga gas sources of p++-In Ga N layer is 10.6% and the thickness of p++-In Ga N layer is 3 nm, the lowest specific contact resistivity of 3.98×10-5?·cm2is achieved. In addition, the experimental results indicate that the specific contact resistivity can be further lowered to1.07×10-7?·cm2by optimizing the alloying annealing temperature to 520℃ .