| Summary: | 碩士 === 國立成功大學 === 微電子工程研究所碩博士班 === 97 === To improve the optoelectronic characteristics and low frequency noise of GaN/AlGaN metal-semiconductor-metal photodetectors (MSM-PDs), the chlorination surface treatment is applied in fabrication. Furthermore, a photoelectrochemical oxidation method is used to directly grow the oxide film of GaN between the interdigital electrodes of GaN/AlGaN MSM-PDs. This acts as a passivation layer to improve the characteristics of GaN/AlGaN MSM-PDs. The interface between metal and semiconductors is important for GaN-based devices due to the existence of surface states and Ga dangling bonds growth using metalorganic chemical vapor deposition (MOCVD). The surface states and Ga dangling bonds degrade the performance of GaN-based devices. The internal gain which attributed to the surface states can be suppressed by the chlorination surface treatment. The products of quantum efficiency and internal gain of the GaN/AlGaN MSM-PDs with and without chlorination surface treatment under a voltage of 5 V at a wavelength of 360 nm is 180.0% and 44.2%, respectively. The UV-visible rejection ratio of 6.67×102 and 7.32×101 was obtained for the GaN/AlGaN MSN-PDs with and without chlorination surface treatment. Besides, the process of oxide passivation grow by PEC can even more reduce the surface states and decrease the reflectivity on the surface of GaN. The products of quantum efficiency and internal gain of the GaN/AlGaN MSM-PDs with oxide passivation can be increase to 47.6%. The UV-visible rejection ratio of 8.20×102 was obtained.
The chlorination surface treatment effectively brings about a reduction on the surface state density of GaN samples. The Schottky contact of the chlorine-treated GaN/AlGaN MSM-PDs is also improved, so that the level of low frequency noise can efficiently be reduced. Furthermore, the process of oxide passivation can even more suppress the level of low frequency noise of GaN/AlGaN MSM-PDs. The noise equivalent power for the untreated, chlorine-treated, and oxide-passivated MSM-PDs, operated at 5 V, was 6.68×10–12 W, 1.60×10–12 W, and 1.28×10–12 W, respectively. The normalized detectivity for the untreated, chlorine-treated, and oxide-passivated MSM-PDs, operated at 5 V, was 4.7×1010 cmHz0.5W–1, 1.9×1011 cmHz0.5W–1, and 2.5×1011 cmHz0.5W–1, respectively.
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