Shen Guang-di

ICP dry etching ITO to improve the performance of GaN-based LEDs

In order to improve the light efficiency of the conventional GaN-based light-emitting diodes (LEDs), the indium tin oxide (ITO) film is introduced as the current spreading layer and the light anti-reflecting layer on the p-GaN surface. There is a big problem with the ITO thin films corrosion during the electrode preparation. In this paper, at least, the edge of the ITO film was lateral corroded 3.5 μm width, i.e. 6.43%-1/3 of ITO films area. An optimized simple process, i.e. inductively couple plasma (ICP), was introduced to solve this problem. The ICP process not only prevented the ITO film from lateral corrosion, but also improved the LEDs light intensity and device performance. The edge of the ITO film by ICP dry etching is steep, and the areas of ITO film are whole. Compared with the chip by wet etching, the areas of light emission increase by 6.43% at least and the chips lop values increase by 45.9% at most.

Reduction of the Far-Field Divergence Angle of an 850 nm Multi-Leaf Holey Vertical Cavity Surface Emitting Laser

By introducing multi-leaf sectorial holes into an oxidation confined 850 nm vertical cavity surface emitting laser (VCSEL), the far-field divergence angle is reduced. The finite-difference time-domain method is used to simulate the far-field pattern of the multi-leaf holey VCSEL with different etching depths and different shapes of the oxide aperture in diameter R. Based on the simulation result, we design and fabricate a multi-leaf holey VCSEL and its divergence angle is only 6°. The experimental results agree well with the theoretical predication.

Reliability of AlGaInP light emitting diodes with an ITO current spreading layer

Three aging experiments were performed for AlGaInP light emitting diodes (LED) with or without indium tin oxide (ITO), which is used as a current spreading layer. It was found that the voltage of the LED with an ITO film increased at a high current stressing, while there was little change for that of the LED without the ITO. The results of the LEDs with different thicknesses of the ITO film show that the LED with a thicker ITO has a higher reliability. The main reason for the voltage increase of the LED with the ITO film might be the current crowding in the ITO film around the P-type electrode.

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.

A rapid evaluation method for degradation activation energy of n-GaAs ohmic contacts with and without TiN diffusion barrier layers

A rapid evaluation method, the temperature ramp method, for GaAs MESFET ohmic contacts is proposed. By use of this method, activation energy for ohmic contact degradation can be obtained using less time and a smaller number of samples than traditional methods, and the results are in agreement with those obtained by traditional methods. In accordance with some drawbacks of traditional AuGeNi-Au ohmic contacts, a new ohmic contacts system with TiN diffusion barrier layer is proposed. Experimental results show that the reliability of ohmic contacts with TiN is greatly superior to that of traditional AuGeNi-Au ohmic contacts.

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.

Improved light extraction in AlGaInP-based LEDs using a self-assembly metal nanomask

This paper reports a new method of fabricating AlGaInP-based nanorod light emitting diodes (LEDs) by using self-assembly metal layer nanomasks and inductively coupled plasma. Light-power measurements indicate that the scattering of photons considerably enhances the probability of escaping from the nanorod LEDs. The light-intensity of the nanorod LED is increased by 34% for a thin GaP window layer, and by 17% for an 8 μm GaP window layer. The light-power of the nanorod LED is increased by 25% and 13%, respectively.

A Single-Fundamental-Mode Photonic Crystal Vertical Cavity Surface Emitting Laser

Single-fundamental-mode photonic crystal (PhC) vertical cavity surface emitting lasers (VCSEL) are produced and their single-fundamental-mode performances are investigated and demonstrated. A two-dimensional PhC with single-point-defect structure is fabricated using UV photolithography and inductive coupled plasma reactive ion etching on the surface of the VCSELs top distributed Bragg-reflector. The PhC VCSEL maintains single-fundamental-mode operating with output power 1.7 mW and threshold current 2.5 mA. The full width half maximum of the lasing spectrum is less than 0.1 nm, the far field divergence angle is less than 10 degrees and the side mode suppression ratio is over 35 dB. The device characteristics are analyzed based on the effective index model of the photonic crystal fiber. The experimental results agree well with the theoretical expectation.