The Study On Direct-/Alternating-current Driving Electroluminescence And Doping Of Nc-Si/SiO₂Multilayers

In the last decades the electronic and optical properties of nanocrystalline silicon (nc-Si) have attracted a lot of attention because of the possible use in silicon-based nano-electronics and optoelectronics as well as on-chip monolithic optoelectronic integration. In this thesis, the structure and optoelectronic characteristics of nc-Si/SiO2multilayered device were investigated. The un-doped and P-doped amorphous Si/SiO2multilayers (MLs) were deposited by PECVD system and nc-Si was obtained after thermal annealing. The Al electrode on back side and ITO on front side were deposited by thermal evaporation and electron beam evaporation, respectively. The film microstructures were characterized by Raman and TEM. Photoluminescence and electroluminescence properties were discussed in the visible and infrared region. For P-doped nc-Si, the electronic structure was studied by XPS and ESR and the effects of doping concentration and annealing temperature on luminescence were discussed.The main results of this thesis are as follows:1. We have fabricated nc-Si/SiO2multilayered prototype device containing nc-Si of high density and controllable size. PL at780nm and890nm were observed and are attributed to the recombination in nc-Si and at the nc-Si/SiO2interface states, respectively. Besides the light emission in nc-Si, an EL peak at1150nm in the infrared region was detected, which comes from the e-h pairs recombination at the p-Si substrate/SiO2interface. The current-voltage curve of our device showed that direct tunneling and FN tunneling dominate in low (<3V) and high field region (>7.2V), respectively. It is also demonstrated by Z parameter that the total current are composed of defect and e-h pair recombination related currents, which implies that the EL is originated from the co-contribution of electron-hole recombination within nc-Si and via the localized states in nc-Si/SiO2interfaces.2. We observed EL with peak at around900nm when the device was operated under sinusoidal wave function. The EL peak and intensity are both frequency-dependent. We estimate the time scale of the first carrier tunneling into the neutral nc-Si, the radiative recombination in nc-Si and the MOS capacitor charge/diacharge to be140μs,25μs and4μs, respectively. We found that the main components in total current are also frequency-dependent. When driven by square wave the EL properties are much like that under direct current. We also found that the device showed better stability when driven by ac rather than dc.3. P-doped nc-Si/SiO2MLs were deposited with nc-Si density of4.2×1012cm-2. The multilayered structures and phase separation of Si and SiO2were characterized by XPS. P atoms were found to be repelled out of SiO2and incorporated into nc-Si after high temperature annealing. The ESR experiments demonstrated the existance of Si dangling bonds (Si DBs) defects at nc-Si/SiO2interface, which can be reduced by P doping. It suggests that P atom be at the interface states and passivate Si DBs. After P doping another defect Pb/E appeared. Moreover, we observed the conduction electron resonance signal even at low P concentration.