| Summary: | 碩士 === 國立成功大學 === 光電科學與工程研究所 === 93 === In this dissertation, we have designed a set of methods to predict the relative parameters of GaN LED epi-wafer before the process. Accordingly, we can avoid processing the epi-wafers that we have predicted that they will have poor device quality . By means of this, we can reduce a great number of costs. The prediction parameters include forward voltage(Vf), dominant wavelength(λd), peak wavelength(λp), Full Width at Half Maximum(Δλ), break down voltage(Vr), leakage current(Ir)and electroluminescence intensity(Iv).
In the prediction of Vf, λd, λp and Δλ, because we have the problem of p-GaN whose resistivity is too high, we have to add a current spreading layer on p-GaN to drive the inject current to 20mA so as to directly predict the value of Vf, λd, λp and Δλ. As to the prediction of optical properties, such as λd, λp and Δλ, the prediction is quite accurate. In terms of the prediction of Vf, the difference between the prediction and the result always keeps in a constant. Therefore this prediction of Vf is also applicable.
In the prediction of Vr, Ir and Iv, we take three epi-wafers to measure their dead current. This is because dead current absolutely has relation with the active layer of LED. The higher the dead current is, the poor quality the active layer will has. Thus, we can make the values of dead current, Vr, Ir and Iv a graph. Afterward, we can relatively predict the values of Vr, Ir and Iv of the fourth epi-wafer through the dead current of the fourth epi-wafer that we have measured first.
Finally, we find that after the probes damage the epi-wafer, there will be a burned hole in the surface of the epi-wafer. We know that the hole has great relation with the practice of the prediction. So we make use of AFM to measure the depth and current distribution of the hole. We eventually find there is a great value of current spreading in the ramp and the bottom of the hole. The current is hundreds of times higher than usual one. Because the sudden increase of the current, we can drive the inject current upto 20mA before the process and successfully predict the parameters of the epi-wafers.
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