| Summary: | 碩士 === 國立交通大學 === 電機學院電子與光電學程 === 102 === In this thesis, we researched the electrical &; optical characteristics of different reflective materials and different deposition rates for AlGaInP Red LEDs with bonding process. We compared the electrical-optical performance of different reflective materials in this research. There are four materials chose, Ag, Au, Al, Pt. The result showed that Ag had the best optical LED performance, followed by Au and Pt. Al was the worst one. A high temperature alloy treatment was designed in the LED process. Then oxidation issue occurs for Al. So that reflectivity of Al turned to low, even that was higher than Pt before alloy. Not only output power, but also the variation of forward voltage was influenced. Increasing ratio of forward voltage was even higher while increasing the driving current, especially at high current condition.
Furthermore we do researches on surface morphology of each material, three different deposition rates designed to observe the different surface roughness. The result shows that with the deposition rate becomes high, the surface roughness will change to be a smooth one, low deposition rate will get a rougher surface morphology. Deposition rate and the surface roughness are inversely proportional. Surface roughness will affect the performance of reflectivity. If we compare the reflectivity with deposition rate, the higher deposition rate will have the higher reflectivity. On the contrary, the lower deposition rate will have the lower reflectivity. In our researches, except these two observations that we discussed above, we also observe the variation of electrical-optical characteristics. Higher output power can be obtained by higher deposition rate; oppositely, lower deposition rate leads to lower output power, because of surface roughness.
In our experiments, the maximum deposition rate is 3.0Å/s, the minimum deposition rate is 0.5Å/s. For LED with Au material, we can have a 9.76% enhancement with injection current 20mA. For LED with Ag material, the enhancement is 9.41%.
We also observed that the variations of the external quantum efficiency by XRD analysis. While increasing the deposition rate, the grain size of reflective mirror becomes larger. But ITO surface will been damaged by the evaporated atoms with higher dynamic energy that accelerated by electron beam voltage in higher deposition rate. This result leads to that forward voltage became larger at higher injection current. External quantum efficiency droop occurred more obviously. In our experiments, efficiency droop begins when the current is higher than about 150mA with a 10mil*10mil chip size.
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