چكيده به لاتين
In this study, the photodiode is obtained from two semiconductor bonds, one with a positive type (with additional holes with a positive charge), and other negative type (with additional electrons with a negative charge). When the photodiode is exposed to light, the carriers, in the absence of light, do not have enough energy to overcome the potential barrier, due to the imbalance of charges on the two photodiode poles, by acquiring energy from the incident light, overcomes the potential barrier, and the electric current lighting is produced by converting light into an electrical signal. In this process, the proper selection of the three main components of the photodiode, the substrate, the light sensitive material, and the electrode material of the carrier collector, greatly contribute to optimizing the basic parameters of the device. In this dissertation, after selection of positive type silicon as substrate and negative type of ZnO as a light sensitive material, hybrid structures were used to optimize heterogeneous photodiode parameters, which include: 1) optimization of aluminum ion by chemical method on the structure of ZnO, for the proper increase of the carriers in the ZnO: Al. 2) Using a graphene quantum dots layer as a hybrid structure (ZnO: Al / GQD / ZnO: Al) to reduce the photodiode dark current and 3) Optimizing the Hybrid electrode to reduce the contact resistance and increase the output of the device.
After chemical synthesis and optimization of elemental compounds in the required layers, a solution of 1 molar Zinc acetate at a concentration of 2% aluminum atom was selected due to better electrical properties to create a light-sensitive layer. In order to create metal contacts, titanium, aluminum and gold (TIi, Al, Au) were used on the ZnO:Al layer. Using a circular TLM scheme, the lithography of the specimens, the special contact resistance between metal contacts and semiconductor was measured with great precision. After the annealing of the samples at different temperatures, the current-voltage characteristic was performed to confirm the reduction of contact and also to find the best annealing temperature with a special contact resistance. The results showed that the metal hybrid structures used at an annealing temperature of 350 ℃ had the minimum contact resistance of 10-7 Ω. cm2. Also, by studying the current-voltage characteristic of the samples, it was concluded that photodiodes made of an optimum concentration of 1 molar of zinc acetate and 2% of aluminum impurities, under ultraviolet radiation, exhibited the best photo current, and samples with graphene quantum dots annealed at an optimum temperature of 400 ° C, although having less photo current, showed a very small dark current, and the signal-to-noise ratio of samples with a GQD layer, at 2 volts, was around 600. Also, the response time of these samples (ZnO:Al/GQD/ZnO:Al) was 14 times faster than the ZnO:Al photodiodes, and the effect of the quantum dot layer in the form of a hybrid structure was found to decrease the response time.
