Application Of Si Quantum Dots In Energy Band Regulation Of Hetero-interface And Charge Memory

Silicon quantum dots (QDs) have been widely applied in photoelectric and other microelectronic devices due to their unique quantum effect. In this study, we explained the preparation technique process of Si QDs by PECVD and thermal annealing technologies, and analyzed the silicon-rich a-SiC:H films prepared under different annealing conditions. The results demonstrate the forming of Si QDs in the films after annealing. The silicon-rich a-SiC:H/c-Si heterostructure was fabricated by PECVD, and after annealing, the Si QDs in a-SiC:H/c-Si heterostructure formed, for regulation of energy band alignment at hetero-interface. Through changing the annealing conditions, the relation between the microstructure of Si QDs and the energy band alignment at the hetero-interface was study. The optical band gap of the Si-rich a-SiC:H film depends on the ordering of the microstructure, the crystallinity, the sizes of the QDs, and the proportion of SiC QDs. The energy band alignment at the hetero-interface was influenced by the crystallinity and ordered structure of the Si-rich a-SiC:H films. The determined energy band alignment contributes to understanding the carrier transport mechanism and designing QDs/c-Si heterojunction devices.To study the application prospect of Si QDs materials in the regulation of energy band alignment at silicon-based hetero-interfaces, the influence of energy band alignment at silicon-based hetero-interfaces of heterojunction solar cells on the interface carrier transport property was studied by simulation. Through analysis of interfaces transport mechanisms and improvement of interfaces transport quality of the silicon-based heterojunction solar cell with the efficiency of 27.37%was obtained by simulation. In addition, boron-doped ZnO (BZO) films were grown and applied in bifacial a-Si:H/c-Si heterojunction solar cell by MOCVD. The microstructure, optical and electrical properties of BZO films were influenced by the B2H6 flow rate and substrate temperature. The optimum BZO films with resistivity of 0.9-1.0×10-3 ? cm, mobility of 16.5?25.5 cm2/Vs and carrier concentration of 2.2-2.7×1020 cm-3 were obtained at B2H6 flow rate of-10 sccm and substrate temperature of-170 ?. The optimized BZO films were applied in silicon-based heterojunction solar cell as the transparent electrodes. The heterojunction solar cell with efficiency of 17.788% (Voc-0.628 V, JSc:41.756 mA/cm2 and FF:0.678) was obtained. It was better than the performance (?:16.443%, Voc:0.590 V, Jsc:36.515 mA/cm2 and FF:0.762) of the bifacial solar cell with ITO films as transparency electrodes.On the application of Si QDs in charge memory, the capacitor memory with Si QDs embedded in a-SiC:H film as charge storage layer was fabricated, and the charging/discharging process and mechanism of Si QDs were studied. The C-V curves demonstrate the charge storage behavior. The shift of conductance peaks in G-V curves demonstrates the carrier transfer between Si QDs and Si substrate. The analysis results reveal that most of Si QDs embedded in a-SiC:H film have Coulomb charging energy that is greater than the thermal energy at room temperature so that the majority of Si QDs exhibit the Coulomb blockade effect. The Si QDs with large diameter or low charging energy are able to trap two or more electrons by increasing the charging voltage. In the charging/discharging process of Si QDs, the trapped probability of carrier by Si QDs depends on the potential barrier height between Si QD and a-SiC:H, and the size of Si QDs. It is found that the lower potential barrier and Coulomb charging energy can enhance the charging/discharging effect of Si QDs and then result in larger memory window.