Weiling Guo

High efficiency tunneling-regenerated multi-active region light-emitting diodes

A new mechanism of tunneling-regenerated multi-active region LEDs with high quantum efficiency and high brightness has been presented. The layer structure, MOCVD growth, device technology, a several of measured curves and their analysis of these new mechanism LEDs were shown in the paper. It was theoretically and experimentally resulted in that efficiency of the electro-luminescence and the on-axis luminous intensity can linearly increase approximately with the number of active regions.

A study of thermal properties of power AlGaInP and InGaN LEDs

III-V compound semiconductor visible-spectrum light-emitting diodes (LEDs) have received much attention for their important applications in several areas. The AlGaInP semiconductor materials are capable of emitting light of red and orange, and the InGaN semiconductor materials are capable of emitting light of green and blue. Those four colors of LED chips are encapsulated with epoxy in same conditions. In this paper, the junction temperature of power AlGaInP and InGaN LEDs were measured at different drive current by forward - voltage method .Optical and electrical parameters under different temperature were also measured. Thermal properties of power AlGaInP and InGaN LEDs were analyzed for strong dependence of optical and electrical characteristics of power light-emitting diodes on the diode junction temperature.

The reliability of tunnel junction regenerated light emitting diodes

The theory of Light Emitting Diodes(LEDs) life tests and mathematic model of life tests were introduced. The performance of LEDs was affected by the drive current and by the ambient temperature. Life tests of tunnel junction regenerated AlGaInP LEDs were performed at different currents and ambient temperatures. On axis output intensity of tunnel junction regenerated LED had decreased 35.53% after 5203 hours at 30mA and 25°C. At the ambient temperature of 80°C, on axis output intensity of tunnel junction regenerated LED had degraded 19.26% after 3888 hours at 20mA. According to the results mentioned above, the normal working lifetime of tunnel junction regenerated LEDs were concluded. Moreover, the main Failure Mechanisms of it were described. Our work reviews the failure analysis that was performed on the degraded LEDs and the degradation mechanisms that were identified. The results show a thermal degradation mechanism that dominates degradation at high ambient temperatures.

Thermal analysis of InGaAs/AlGaAs quantum well lasers diode by atomic force microscope (AFM)

In this paper, a 4 /spl mu/m ridge waveguide 980 nm InGaAs/AlGaAs quantum well laser diode is fabricated. It shows excellent optical and electrical characteristics. The output power is 68 mW with a threshold current of 35 mA. The far-field pattern shows fundamental transverse mode operation. Thermal properties of the diodes are presented by atomic force microscope (AFM) images. They clearly show the filling layer of SiO/sub 2/ near the ridge and that the active layer is the more thermal area in the cavity surface. The optical and electrical properties of 100 /spl mu/m wide stripe laser diodes are studied and thermal analysis is performed through the threshold current density at different operation temperatures.

Thermal and optical properties of power LEDs

With the increased efficiency of high power LED, the thermal design of the device used LEDs become more important. In this paper, four kinds of white power LEDs were selected, and the aim of this study was to compare the thermal and optical properties of the white power LEDs from different LED vendors, and to find LEDs with the optimal properties. Moreover, each group of LEDs was made into bulbs of different watts, respectively. The characteristics of these bulbs are also tested, and the relationship between the temperature and the luminous efficiency is obtained.

Two different lasers integrated in a monochip by one-step epitaxy

A new way to integrate two different lasers (LD1: 950 nm and LD2: 990 nm) in a monochip by one-step epitaxial growth is presented. These two lasers are cascaded by a high-doping tunnel junction that separates the two active regions so that a four-terminal device can be implemented, which permits the operation of the lasers electrically independent as LD1, LD2, and LD1+LD2 after fabrication process. High power dual-wavelength operation laser diodes are fabricated, output power as high as 3.1 W at 3 A and 2.4 W at 2 A is obtained, and the slope efficiency can reach 1.38 W/A. As for four-terminal integrated laser diodes, the threshold current is 54, 58, and 65 mA, and the slope efficiency is 0.73, 0.48, and 0.37 for the LD1+LD2, LD1, and LD2, respectively.

The effect of temperature on the color temperature of GaN-based LED

In this paper, two kinds of GaN-based light emitting diodes (LED) with difference in color temperature were tested under the temperature range from 283K to 353K and current of 350mA. The samples were fabricated with the same blue-ray chip but coated by different yttrium aluminum garnet (YAG) phosphor. After analyzing the PL spectrum, the result shows that the color temperature of LED increases while temperature raising, whats more, the cool-color-temperature LED increases more. It also proves that the color temperature of GaN-based write LED has relation to the proportion of blue ray radiant flux.

AlGaInP thin-film LED with ITO omni-directional reflector

Four kinds of thin-film light emitting diodes (LEDs), with different metal reflectors and different thickness indium tin oxide (ITO) layers, were fabricated from the same AlGaInP/GaAs epitaxial layer. For comparison, three kinds of LEDs have the same ITO/AuZnAu reflector, but have different thickness of ITO film 65, 90 and 270nm, respectively. The device with 65nm ITO film provides the best luminous intensity-current (L-I) and injection current-forward voltage (I–V) performance, which has the luminous intensity of 149.2 mcd (@20mA) and the forward voltage of 2.15v (@20mA). In addition, two kinds of LEDs have the same 90nm ITO layer, but have different reflector ITO/AuZnAu and ITO/Au, respectively. The LED with ITO/AuZnAu reflector has better optical and electrical properties. The possible reason may be the diffusion of Zn content into the ITO layer and GaP layer. The influences of Zn content and the thickness of ITO film to the optical and electrical properties of the LEDs are discussed in this paper.

Sulfuric acid corrosion of ITO surface for improvement of the optical properties

After the surface treatment with concentrate sulfuric acid, the sheet resistance of ITO layer is unchanged, while the surface roughness increased. When the 70–100nm ITO layer is eroded by the concentrate sulfuric acid for 480 seconds, its reflectivity decreased and the transmittance significantly increased. It can improve the optical properties of the LED devices.

Thermal resistance analysis of high power light emitting diodes

Thermal characteristic of light emitting diodes is one of primary reliability parameters. In this paper, the thermal resistances of different kinds of blue and white high power LEDs are measured by the forward voltage based method. The relationships between thermal resistance and heat time at measurement currents 1mA, 5mA and 10mA are obtained respectively. The results show that there is optimum heat balance time of 300∼1200s to measure the thermal resistances at room temperature. The influence of current crowding, the phosphor and heat sink to the thermal resistance has been demonstrated.