| Summary: | 碩士 === 國立高雄應用科技大學 === 電子與資訊工程研究所碩士班 === 91 === In this study, the LED devices were passivated by (NH4 )2Sx, and we can see the leakage current reduced by 2 ~ 3 orders and the brightness of the chip increased to 12%.
We used SPMs (Scanning probe microscopes) to observe the roughness on the surface to prove the reason is not due to surface roughness, nor is the reduction of the fresnel loss. PL measurement is also illustrated to show that the PL intensity of the sample with sulfidation is weaker than the as-fabricated one. It shows that the surface with sulfidation is smoother than an untreated one. Sulfidation cannot roughen the semiconductor surface to make the light extraction better.
I-V characteristic curve measured by HP4156 shows that the leakage current of the device with passivation is smaller than an as-fabricated one, and the device was measured at different temperatures to derive the activation energy of the sulfur treated samples, and the bandgap of a sample with sulfidation is found to be 2 eV, close to the ideal diode. (Note: The bandgap of (AlxGa1-x)0.5In0.5P is equal to 1.91 + 0.61x). Excellent passivation makes the sulfur treated device more ideal.
In short, sulfidation treatment can make devices brighter than as-fabricated ones and the reason is not due to surface roughness.
Ammonium sulfide is able to decrease the surface states and repair the defects or dangling bonds occurring at the perimeter junction and diminish the leakage channel.
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