Fabrication of Porous Silicon Diode by electrochemical anodic etching

• Main Authors: Kang-Chih Liu, 劉康志
• Other Authors: 賴聰賢
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/d6a255

碩士 === 國立中興大學 === 光電工程研究所 === 106 === In this thesis, the porous silicon was formed by electrochemical etching of P-type (100) wafer in different hydrofluoric electrolyte concentration at the constant current density of 5 mA/cm2 for different etching time. We observed the SEM image reveals that PSi pores like dendritic structure, and the structure will be formed according to the shorter diffusion length of the diffusion limiting model. Besides, the thickness of PSi will become 4.5 μm after 30 min of etching. Raman spectrum of PSi was found the FWHM was wider than that of the single crystal silicon, so it could be speculate the reason of FWHM became wider due to the increase of porosity. The Porous silicon which was prepared was divided into two parts for research, first part of the samples was demonstrated with ZnO on different cycles by atomic layer deposition technique (ALD), and the deposition of ZnO 100 cycles (21.10 nm) produces the largest blue shift up to 34 nm; and the second part was used a non-toxic InP/ZnS quantum dots were dropped on the PSi surface, and the red shift phenomenon was apparently observed. It was found that the higher QD concentration did not increase the strength. The ZnO 100 cycles were first deposition on QD/PSi surface, and then AZO (15 nm) is plated on top to form n+-type. PL spectrum had shown that the deposited ZnO was much stronger than QD/PSi. Especially, CHF=12.5% with etching time 10 min showed double peaks of 606 nm and 690 nm. It can be inferred that the broad spectrum is caused by the intrinsic defects of ZnO, porous silicon and QD. The device of the first part with metal coated was analyzed by I-V curve and EL spectrum, but it was found that the metal contact did not form an ohmic contact, which resulted in higher resistance contact, so the AZO/ZnO/QD/PSi structure was used to improve this problem. Log(I)-V characteristics of ZnO/PSi structure can know ideality factor. A ideality factor of 5.75 at etching time 30 min. The longer of etching time, the larger surface roughness and series resistance of the device, it caused the ideality factor larger than the ideal diode. In the EL spectrum, the etching time of ZnO (50, 100 cycles)/PSi structure was 25 and 30 min, and the peak near 450 nm was obvious. It could be inferred that this peak was the blue-green band excited by the ZnO intrinsic defects.