Tiecheng Gao

Enhancing the Light Extraction Efficiency of GaN-based LEDs

GaN-based light-emitting diode (LED) has been widely used in recent years, and tremendous progress has been achieved in GaN-based semiconductor materials and relevant process. However, owing to the large refractive index contrast between GaN-based semiconductor materials and air, light can be easily totally internally reflected at the semiconductor/air interface, and the critical angle for light to escape from the semiconductor is small. Therefore, the light extraction efficiency for GaN-based LED is still low and needs improving. Some of the leading approaches to enhance light extraction efficiency of GaN-based LED such as surface texturing or roughening, omnidirectional reflectors, photonic crystals, laser liftoff, transparent electrode, patterned substrate and so on are introduced in detail. For each approach, how the variation in device structure or material improves the light extraction efficiency is analyzed thoroughly. At last, some of mentioned approaches that are promising are evaluated and viewed briefly.

The Research of Operational Transconductance Amplifier

A topology structure of operational transconductance amplifier is proposed to be devised in this paper. In order to make it have the feature of high-speed, large bandwidth, and high stability, a two-stage cascode structure amplifier is designed by using cascaded single-stage amplifier. And several important parameters are calculated and analyzed theoretically. Finally the designed cascode two-stage amplifier is debugged by using Hspice. And the related parameter values are obtained. The magnification is more than 100dB, unity gain bandwidth is about 635MHz, and output swing is 4V. And the total transconductance of operational transconductance amplifier is 8.8A / V.

The fabrication of high-brightness and high-power InGaAlP single-side red LED

In this paper, it is reported that the design and fabrication of high-brightness and high-power InGaAlP single-side red LED with electrodes which are interdigitated with the fingers. High-brightness and high-power InGaAlP LED is a new kind of visible light LED developed in recent years, which is driven by large current capacity, high luminous efficiency and excellent heat resistance. It has been used in various fields, such as large area displays, traffic lights, brake lights and so on. As compared with the conventional double-side LED, the single-side LED is more flexible to integrate with other devices and its fabrication is simplified. The size of chip is 1mm2. The fabrication of single-side LED, essentially, is the same as conventional LED, involving photolithography, PECVD SiO2, wet etching, evaporating, lift off and rapid thermal annealing using four masks. To control the widths of mesa and N electrode precisely, the selecting etch technique has been adopted, using HCL: H2O:H2O2 as the InGaAlP etching solution. I-V characteristics, light emission spectrum, luminous flux, luminous intensity and luminous efficiency of this LED have been measured. The characteristics are obtained with turn-on voltage of 1.5V and forward current of 400mA at its forward voltage of 3V. The peak wavelength is 635nm, which corresponds to red light, and the Full Width of Half Maximum is 16.4nm at injection current of 350mA. The luminous intensity is 830 mcd. The color coordinates is x=0.6943, y=0.3056 and the color index is 18.4. So we will conclude that the high-brightness and high-power InGaAlP single-side red LED will become new focus in both scientific research and industrial investment for its wide application.