Bifeng Cui

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.

Computational analysis of flow field in GaAs-MOCVD vertical rotating disk reactor

This paper gives a detailed analysis and discussion of the flow field inside the type of D125 MOCVD reactor chamber through the analysis of three-dimensional mathematical model and calculation. Under a wide range of geometric and process parameters, such as varying total flow rate of gas inlet, chamber pressure, growth temperature, and wafer carrier rotation. It is finally obtained the favorable conditions of the uniform distributions of velocity profiles inside the reactor. The CFD simulating results are beneficial to fixing on the process operating conditions document.

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.

Lateral current spreading in stripe laser diodes

Lateral current spreading is experimentally and theoretically investigated in stripe laser diodes. The influence of current spreading length to threshold current density is quantitatively analyzed. The factors of current spreading length that residual thickness, resistivity of upper cladding layer, injected current density are numerically calculated. It is found that effective current rate declines with the injected current increasing and resistivity affects the current spreading length dramatically. A critical injected current density exists below which the slope efficiency increases with the injected current density increasing. Above this critical value, the slope efficiency declines with the injected current density increasing. This critical value helps to find the best work current, which can extend the lasers life.