Photoluminesence And Field Emission Properties Of Carbon/Silicon Nanoporous Pillar Array

Silicon nanoporous pillar array(Si-NPA) has strong red and weak blue light emission, and as the regular pillar arrays in surface it is good for field emission. In this work, fresh Si-NPAs are prepared by a hydrothermal etching method, and then different Si-NPAs are placed in the etching solution for few hours at room temperature, annealed at different temperature, carbonized at 1100 ℃, individual.Microstructure and photoluminescence are characterized for all the samples.Subsequently, carbon films are deposited on Si-NPAs at different temperature using xylene and ethanol as precursor. Field emission properties are characterized and then optimized. The main research results achieved in this thesis are listed as the followings:1. Si-NPAs are prepared by hydrothermal etching method, and these Si-NAPs are placed in the etching solution for few hours at room temperature. The SEM spectra indicate that the density of silicon pillar increase with the etching time adding.It is obvious that the blue light emission of Si-NPA decrease gradually when the content of oxygen decreasing with the etching time increasing indicated by the EDS and XRD spectra. So the origin of the blue light from oxygen related defect is confirmed. Meanwhile, the red emission of Si-NPA is tunable by increasing the etching time at room temperature.2. Si-NPAs are annealed for 10 min at different temperature(300℃、500℃、700℃、900℃、1100℃). The microstructure of Si-NPAs remain the same, meanwhile the relative intensity of red light emission peak turns weaker gradually, and the relative intensity of blue light emission peak becomes stronger with the temperature increasing. It can be inference that the oxygen related defect increased when more Si O2 is formed at high temperature, it causes that the blue light emission becomes more obvious and the red light emission almost disappears.3. Si-NPAs are carbonized at 1100℃ for few minutes(2 min、4 min、6 min、8min、10 min、12 min、14 min、16 min) using xylene as precursor. The microstructure of Si-NPA carbonized for 6 min has no changes compare to the fresh Si-NPA.Amorphous carbon films are formed on the surface of Si-NPAs as the time of carbonization increasing. For the Si-NPAs carbonized for few minutes(2 min、4 min、6 min、8 min、10 min),their red light emission peak disappear, and the blue light emission peak remain, meanwhile a new emission about 350 nm appears.4. Carbon films are deposited on the Si-NPAs at different temperatures using xylene as precursor for 40 min and ethanol as precursor for 15 min. Thickness of carbon films increase gradually and then decrease, the thickness of the interface of Si C increase with the temperature increasing. The turn-on fields of C/Si-NPAs increase first and then decrease with the temperature varying from 800℃ to 1100℃,it means that there is a optimal temperature for xylene(1000℃) and ethanol(950℃)keeping the time of deposition at a constant. These indicated that the turn-on field is related to the thickness of carbon film and the interface of Si C.5. Optimization scheme is taken out to low the turn-on fields down by changing the time of carbon deposition at the optimal temperature. Obviously, the thickness of carbon films increase with the deposit time increase. However, the intensity of the Raman peak of Si C increases. It is found that the turn-on fields do not decrease when the deposit time increase. So, it inferences that there is a optimal thickness of Si C interface for the field emission, the turn-on fields would raise up if the thickness of Si C is big than the optimal value.6. In order to have more time for carbon deposition before the thickness of the Si C interface reach the optimal value, the carbon deposit temperature is set as 900℃.In this program, the turn-on fields decrease with the time of carbon deposition increasing. As a result, the field emission properties of the C/Si-NPAs are optimized,a smallest turn-on field is obtained about 1.77 V/μm.