Liu Shi-Yong

Self-Aligned InP/InGaAs Single Heterojunction Bipolar Transistor with Novel Micro-airbridge Structure and Quasi-coplanar Contacts

The fabrication and performance of a self-aligned InP/InGaAs single heterojunction bipolar transistor (SHBT) with a novel micro-airbridge structure and co-planar-contacts are described. The reported structure is based on anisotropy wet, etching of InP and selective wet, etching between InP and InGaAs. The device with a 1.5×5 µm2 emitter demonstrates a current gain of 30 at collector current Ic = 10 mA and extrapolates the current-gain cutoff frequency Ft of 53 GHz and the maximum oscillation frequency Fmax of 72 GHz. Compared with the one using the conventional structure, the maximum oscillation frequency of the device with micro-airbridge is dramatically improved from 45 GHz to 72 GHz. This result reveals that the extrinsic capacitance of small size SHBT can be greatly reduced.

Influence of the Energy Level Matching on the Performances of Organic/Polymeric Electroluminescent Devices

The performances such as the operating-voltage and the brightness of three types of devices: single-layer device, double-layer device and three-layer device, were examined. It is demonstrated that the I-V characteristics of single-layer device depends not on the applied voltage but instead on the electric-field strength, and the brightness increased by a factor of 50 and the operating-voltage decreased when introducing one electron transporting layer or an electron transporting layer and one hole blocking layer between the light emitting layer and the negative electrode. In fact, it is imperative to match the energy level of each layer in the electroluminescent device in order to improve its comprehensive performances.

High-Efficiency White Organic Light-Emitting Devices Based on Multiple Quantum-Well Structure

We report the white organic-light devices (WOLEDs) employing a multiple quantum-well (MQW) structure, which consist of alternate layers of 4,48-bis(2,28-diphenylvinyl)-1,18-biphenyl (DPVBi) and (DPVBi:rubrene) as the potential barrier and the potential well, respectively. The results demonstrate that the MQW structure can prominently increase the performance of WOLEDs; the double quantum well device exhibits the efficiency up to 5.4 cd/A, and yields a peak luminance of 14206 cd/m2. It is also interesting to find that the MQW structure can enhance the colour stability of WOLEDs at different voltages.

High-Efficient Organic Light-Emitting Diodes Using Indium Tin Oxide Treated by KMnO4 Solution as Anode

High-efficient organic light-emitting diodes (OLEDs) with indium-tin-oxide (ITO) anode treated by KMnO4 solution are demonstrated. The performance of the OLEDs depends on the concentration of KMnO4 solution and time of ultrasonic treatment. The OLED whose ITO anode was treated by ultrasonic in KMnO4 solution with concentration of 50 mg/L for 15 min displays the best performance. It has higher electroluminescent brightness and lower turn-on voltage than those of traditional devices. In particular, its efficiency can be increased by approximately 40%. The surfaces of the ITO anode with and without treating are analysed by scanning electron microscopy.

Doping in the Mixed Layer to Achieve High Brightness and Efficiency Organic Light Emitting Devices

Doping in the mixed layer was introduced to fabricate high brightness and high efficiency organic light emitting devices. In these devices, a copper phthalocyanine (CuPc) film acts as the buffer layer, a naphthylphenybiphenyl amine (NPB) film as the hole transport layer and a tris(8-hydroxyquinolinolate)aluminium (Alq3) film as the electron transport layer. The luminescent layer consists of the mixture of NPB, Alq3 (to be called the mixed layer), and an emitting dopant 5,6,11,12-petraphenylnaphthacene (rubrene), where the concentration of NPB declined and the concentration of Alq3 was increased gradually in the deposition process. Adopting this doping mixed layer, the device exhibits the maximum emission of 49300 cd/m2 at 35 V and the maximum efficiency of 7.96 cd/A at 10.5 V, which have been improved by two times in comparison with conventional doped devices. We attribute this improvement to the effective confinement of carriers in the mixed layer, which leads to the increase of the recombination efficiency of carriers.

Flexible Blue Light Emitting Diodes Made from Dye Doped Poly(N-Vinylcarbazole) with Multilayer Structure

Flexible blue light emitting diodes (LEDs) were fabricated by using poly(N-vinylcarbazole) (PVK) doped with high fluorescence dye, 1, 1, 4, 4-tetraphenyl-1,3-butadiene (TPB), as a emitter layer, a layer of tris(8-quinolinolato)aluminum (III) (Alq3) as an electron-transporting layer, and a layer of 2-(4-biphenylyl)-5-(4-tertbutypheny)-1-3,4-oxadiazole (PBD) as hole-blocking layer; a cell structure of flexible substrate/indium-tin-oxide /PVK:TPB/PBD/Alq3/Al was employed. In this cell structure, carrier injection from the electrodes to the doped PVK layer and concomitant electroluminescence from doped PVK were observed at room temperature with dc bias voltage of 4 V. Blue emission peaks at about 465 nm. This kind of LED is about 200 ?m thick and can be curled or bent repeatedly at sharp angles without failure.

Carriers Confinement for Polymer Electroluminescent Devices with Multilayer Structure

The polymer electroluminescence (EL) device with PBD as carriers confinement layer yields bright blue emission having intensity of 300 cd/m2, in same case the device without PBD layer have luminance only 44 cd/m2. The effect of PBD layer on EL characteristic was studied. The results show that only in EL devices with PBD thickness over 30 nm, the holes are completely confined in emitting layer. The luminance over 2000 cd/m2 can be obtained by inserting an electron injecting layer between the negative electrode and PBD to increase the electron injection.

Blue-Green Electroluminescent Diodes Utilizing Tris (8-Quinolinolato)-Aluminum Doped Poly (Vinylcarbazole)

Blue-green electroluminescent diodes utilizing tris (8-quinolinolato)-aluminum doped poly (vinylcarbazole) have been demonstrated. A Schottky-type electroluminescent diode of the polymer film is driven at 20 V and has a peak emission wavelength of 490 nm at room temperature with lifetime up to 4 h.

White Hybrid Light-Emitting Devices Based on the Emission of Thermal Annealed Ternary CdSe/ZnS Quantum Dots

We report on a white hybrid light-emitting device employing a mixture of ternary CdSe/ZnS quantum dots (QDs) as an emitting layer (EML) and a small molecular material tris(8-hydroxyquinoline) aluminum (Alq3) as an electron-transporting layer. The film morphology of the spin-coated mixture of QDs is strongly improved via thermal annealing, and therefore a close-packed QD-EML is realized between organic charge-transporting layers. As a result, compared to the device with an unannealed QD-EML, the emission of Alq3 is deeply suppressed. In addition, a maximum luminance of more than 1000 cd/m2 and a maximum luminous efficiency of 2.2 cd/A are achieved.

Blue Electroluminescent Diodes Utilizing Blend of Poly (2, 5-Dibutoxyphenylene) in Poly (N-Vinylcarbazole)

Blue emission from polymer blends composed of poly (2,5-dibutoxyphenyiene) (PPP) in a matrix polymer poly (N-vinylcarbazole) (PVK) is reported. The light-emitting layer can be fabricated by spin-coating of PPP-PVK blend solution without subsequent processing or heat treatment. A cell structure of glass substrate /indium-tin-oxide /PPP-PVK blend/aluminum is employed. Blue light emission with a peak position at 448 nm occurs at a bias of about 8 V.