Zou Deshu

A MOCCII current-mode KHN filter and its non-ideal characteristic research

A KHN (Kerwin-Huelsman-Newcomb) current-mode filter circuit based on MOCCII (second generation current conveyor with multiple outputs) is present. The circuit, which is constructed by three MOCCH and six RC elements, can realize a lowpass filter, a bandpass filter and a highpass filter at same time. By a simple current operation, a bandstop filter and a allpass filter can be obtained. The circuit has a low sensitivity and is integrated conveniently for RC elements are grounded. Compared with voltage-mode KHN filters based CCII (second generation current conveyor), it also has a simper structure and much fewer active elements. The non-ideal characteristic of MOCCII is analyzed, and compensation method is present. In the last, the circuit PSPICE imitation results before compensation and after compensation are given.

High power and high reliability GaN/InGaN flip-chip light-emitting diodes

High-power and high-reliability GaN/InGaN flip-chip light-emitting diodes (FCLEDs) have been demonstrated by employing a flip-chip design, and its fabrication process is developed. FCLED is composed of a LED die and a submount which is integrated with circuits to protect the LED from electrostatic discharge (ESD) damage. The LED die is flip-chip soldered to the submount, and light is extracted through the transparent sapphire substrate instead of an absorbing Ni/Au contact layer as in conventional GaN/InGaN LED epitaxial designs. The optical and electrical characteristics of the FCLED are presented. According to ESD IEC61000-4-2 standard (human body model), the FCLEDs tolerated at least 10 kV ESD shock have ten times more capacity than conventional GaN/InGaN LEDs. It is shown that the light output from the FCLEDs at forward current 350mA with a forward voltage of 3.3 V is 144.68 mW, and 236.59 mW at 1.0 A of forward current. With employing an optimized contact scheme the FCLEDs can easily operate up to 1.0 A without significant power degradation or failure. The life test of FCLEDs is performed at forward current of 200 mA at room temperature. The degradation of the light output power is no more than 9% after 1010.75 h of life test, indicating the excellent reliability. FCLEDs can be used in practice where high power and high reliability are necessary, and allow designs with a reduced number of LEDs.

SiGe/Si HBTs with current gain of negative temperature dependence

In this paper, we analysis the basic principle of SiGe/Si HBTs, design and fabricate power transistors with current gain of negative temperature dependence. The current gain of such transistors decreases from 33 to 20, when the temperature rises from 300 K to 385 K, at the case the quiescent current, I/sub cm/, is 200 mA and V/sub ce/ is 2 V. These power HBTs are to be used in medium power amplifiers.

A tunnel regenerated coupled multi-active-region large optical cavity laser with a high quality beam

A novel coupled multi-active-region large optical cavity structure cascaded by a tunnel junction is proposed to solve the problems of facet catastrophic optical damage (COD) and the large vertical divergence caused by the thin emitting area in conventional laser diodes. For a laser with three active regions, a slope efficiency as high as 1.49 W/A, a vertical divergence angle of 17.4°, and a threshold current density of 271 A/cm2 are achieved. By optimizing the structural parameters, the beam quality is greatly improved, and the level of the COD power increases by more than two times compared with that of the conventional laser.

AlGaInP thin-film LED with omni-directionally reflector and ITO transparent conducting n-type contact

In this paper a novel AlGaInP thin-film light-emitting diode (LED) with omni-directionally reflector (ODR) and transparent conducting indium tin oxide (ITO) n-type contact structure is proposed, and fabrication process is developed. This reflector is realized with the combination of a low-refractive-index dielectric layer and a high reflectivity metal layer. This allows the light emitted or internally reflected downwardly towards the GaAs substrate at any angle of incidence to be reflected towards the top surface of the chip. ITO n-type contact is used for anti-reflection and current spreading layers on the ODR-LED with ITO. The sheet resistance of the ITO films (95 nm) deposited on n-ohmic contact of ODR-LED is of the order 23.5Ω/□ with up to 90% transmittance (above 92% for 590–770 nm) in the visible region of the spectrum. The optical and electrical characteristics of the ODR-LED with ITO are presented and compared to conventional AS-LED and ODR-LED without ITO. It is shown that the light output from the ODR-LED with ITO at forward current 20 mA exceeds that of AS-LED and ODR-LED without ITO by about a factor of 1.63 and 0.16, respectively. A favourable luminous intensity of 218.3 mcd from the ODR-LED with ITO (peak wavelength 620 nm) could be obtained under 20 mA injection, which is 2.63 times and 1.21 times higher than that of AS-LED and ODR-LED without ITO, respectively.

Improved light extraction of wafer-bonded AlGaInP LEDs by surface roughening

By using the wafer bonding technique and wet etching process, a wafer bonded thin film AlGaInP LED with wet etched n-AlGaInP surfaces was fabricated. The morphology of the etched surface exhibits a pyramid-like feature. The wafer was cut into 270 × 270 μm2 chips and then packaged into TO-18 without epoxy resin. With 20-mA current injection, the light intensity and output power of LED-I with surface roughening respectively reach 315 mcd and 4.622 mW, which was 1.7 times higher than that of LED-II without surface roughening. The enhancement of output power in LED-I can be attributed to the pyramid-like surface, which not only reduces the total internal reflection at the semiconductor-air interface but also effectively guides more photons into the escape angle for emission from the LED device.

Analysis of the operating point of a novel multiple-active-region tunneling-regenerated vertical-cavity surface-emitting laser

A novel multiple-active-region tunneling-regenerated vertical-cavity surface-emitting laser (VCSEL) with a greater-than-unity differential quantum efficiency is proposed. This novel VCSEL is expected to have an improved performance, specifically, reduced threshold current and heightened output power. The optimum reflectivity in terms of output power is determined for this novel VCSELs with fixed supply current and series resistance as a parameter. We compare the output power of the novel structure with that of the traditional structure at the same reflectivity and injected current. Also, we compare the threshold current of the novel structure with that of the traditional structure at the same reflectivity and output power. Finally, we prove the advantage of the novel structure in theory.

The multi-emitter Si/SiGe HBT for microwave power application

The design of Si/SiGe HBT for high-frequency microwave power amplification was presented in this paper. The material profile structure of the device was designed. A comb liked structure with 6-fingered emitter was employed for the SiGe HBT. Then the device was fabricated by using the buried metal self-aligned double mesa process and high resistivity substrate in a 3 ¿m manufacture process line. The tested results indicate that the Si/SiGe power HBT reaches the parameters of ß=26, VBC¿10 V, ICM¿180 mA and fT¿3.2 GHz.

Absorption of photons in the thin film AlGaInP light emitting diode

The path of photons in the thin film (TF) light emitting diode (LED) was analyzed. The reflectivity of reflector in AlGaInP TF LED with and without the AlGaInP layer was contrasted. The absorption of the AlGaInP layer was analyzed and then the light extraction was calculated and shown in figure. The TF AlGaInP LED with 8 μm and 0.6 μm GaP was fabricated. At the driving current of 20 mA, the light output power of the latter is 33% higher. For the 0.6 μm GaP LED, the etching of heavily doped GaP except the ohmic contact dot area is advised. The design and optimizing of current spreading between the n-type electrode and the p-type ohmic contact dot need further research.

Improved light extracion efficiency in AlGaInP-Based Diodes (LEDs) by applying a nanohole structure on GaP window layer

In this letter, to enhance light efficiency of AlGaInP-based LEDs, a nanohole structure was applied to GaP window layer by using self-assemble metal layer nano-masks and inductively coupled plasma (ICP). This method has the potential advantage because both the size and density of the nanoholes are controllable. The density of nanoholes varied from 5×108 to 2.8×108 cm−2 and size varied from 180–430 nm while increasing rapid thermal annealing temperature from 350–500°C. By using this surface texturing method, the light intensity and light output power of AlGaInP-based LEDs with textured surface (LED-II) increases 27% and 15% comaparing to LEDs with flat surface (LED-I), respectively.