1. GaN-Based MSM Photodetectors Prepared on Patterned Sapphire Substrates Shoou-Jinn Chang, Member, IEEE, Y. D. Jhou, Y. C. Lin, S. L. Wu, C. H. Chen, T. C. Wen, and L. W. Wu IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 20, NO. 22, NOVEMBER 15, 2008 陳詠升

2. Outline Introduction Experiments Results and discussion Conclusion References

3. Introduction GaN materials exhibit high thermal conductivity and wide direct bandgap. These properties make GaN-based materials excellent light emitters.

4. Experiments 受光面積： 150 × 150μm 2 指叉狀電極： 寬 10μm 長 150μm 10μm GaN 1μm sapphire GaN 1μm Ni/Au sapphire 間距 3μm

5. Results and discussion Fig. 1. AFM images of (a) sample A prepared on conventional flat sapphire substrate and (b) sample B prepared on PSS.

6. Fig. 2. Asymmetrical (102) DCXRD rocking curves for the two samples. ( sample A prepared on conventional flat sapphire substrate and sample B prepared on PSS.) FWHM sample A=561 arcsec sample B=358 arcsec

7. Fig. 3. I-Vcharacteristics of the two fabricated MSM PDs measured in dark.Inset shows photograph of the fabricated devices. ( sample A prepared on conventional flat sapphire substrate and sample B prepared on PSS.)

8. Fig. 4. Spectral responses of (a) sample A prepared on conventional flat sapphire substrate and (b) sample B prepared on PSS. Responsivity 1V sample A =0.03 A/W sampleB=0.31 A/W

9. Fig. 5. Measured responsivity at 360 nm as a function of applied bias for the two PDs. ( sample A prepared on conventional flat sapphire substrate and sample B prepared on PSS.)

10. Conclusion GaN-based UV MSM PDs prepared on PSS and on a conventional flat sapphire substrate were both fabricated. It was found that we could suppress the generation of TD, improve crystal quality, and thus reduce internal gain of the PDs by using PSS.

11. References W. H. Lan, “Wavelength shift of gallium nitride light emitting diode with p-down structure,” IEEE Trans. Electron. Dev., vol. 52, pp.1217– 1219, 2005. S. W. Lee, D. C. Oh, H. Goto, J. S. Ha, H. J. Lee, T. Hanada, M. W.Cho, T. Yao, S. K. Hong, H. Y. Lee, S. R. Cho, J. W. Choi, J. H. Choi,J. H. Jang, J. E. Shin, and J. S. Lee, “Origin of forward leakage current in GaN-based light-emitting devices,” Appl. Phys. Lett., vol. 89, 2006,Article 132117.