| Summary: | 碩士 === 國立成功大學 === 微電子工程研究所碩博士班 === 97 === The main goal of this thesis is the fabrication and investigation of InGaN-based metal-semiconductor-metal (MSM) photodetectors (PDs). The samples used in this experiment were prepared by metal organic chemical vapor deposition system (MOCVD). The use of InGaN alloys offers the possibility of shifting the detection edge from the UV to the VIS (and even the IR) by changing the indium composition in the InGaN layers. PDs in this study were designed to be sensitive in the near UV to violet/blue wavelength range with 0.1 In composition.
First, to enhance the optical properties of MSM PDs, the conventional metal electrodes were replaced with transparent conducting oxides (TCOs) ITO or GZO. Compared with conventional Ni/Au contacts, it was found that we can achieve significantly smaller dark current and larger rejection ratio by using transparent and conductive oxide layers ITO or GZO as electrodes. With the same -10 V applied bias, the dark current of the MSM PDs with ITO and GZO electrodes could be reduced by five orders and three orders, respectively. With the same -5 V applied bias, it was found that the rejection ratios were 95.98 and 70.97 for PDs with ITO and GZO electrodes, respectively.
To achieve high quality Schottky contacts, we inserted an silicon dioxide layer between metal and the semiconductor to fabricated PDs with MIS structures. We adopted two deposition methods to grow SiO2 layer, PECVD and photo-CVD. According to SEM, AFM and ESCA analyses, these indicated that the quality of SiO2 deposited by photo-CVD was reasonably better than by PECVD. Compared with conventional MSM PDs, the dark current measured from MIS PDs were much smaller. With the same -10 V applied bias, the reverse leakage current were 5.66×10-10 A and 3.62×10-11 A for the PDs with SiO2 passivation layer deposited by PECVD and photo-CVD, respectively. Besides, it was found that we could lower the dependence on bias for spectral responses by inserting a SiO2 layer.
Based on the aforementioned results, we apply in situ low-temperature AlN cap layer and unactivated Mg-doped GaN cap layer to the fabrication of InGaN-based PDs. Compared with conventional MSM PDs without cap layers, it was found that we can achieve significantly smaller dark current and larger rejection ratio by inserting in situ grown cap layers. This result could be attributed to the thicker and higher potential barrier and effective surface passivation after inserting in situ grown cap layer. With the same -10 V applied bias, the dark leakage current for PDs without cap layers, with LT-AlN cap layer and with Mg-doped GaN cap layer were 2.37×10-7 A, 1.40×10-13 A and 1.81×10-13 A, respectively. With the same -5 V applied bias, it was found that the rejection ratios were 7.22×102 and 3.83×103 for PDs with LT-AlN cap layer and unactivated Mg-doped GaN cap layer, respectively. Therefore, the performance of InGaN-based MSM PDs could be effectively improved by inserting an in situ grown cap layer.
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