多孔硅的制备条件对其光致发光特性的影响

Effect of Preparation Conditions on Photoluminescence of Porous Silicon

不同的实验条件下制备的多孔硅的光致发光 (PL)特性是不同的 ,这是许多研究产生分歧的主要原因。对比分析了阳极氧化电流密度、阳极氧化时间、溶液浓度以及自然氧化时间对多孔硅光致发光光谱的影响。认为在一定的范围内 ,多孔硅的发光峰位会随电流密度的增大而蓝移 ,要获得较强的发光 ,需要选择合适的电流密度 ;随着腐蚀时间的延长 ,多孔硅的发光峰位也发生蓝移。当HF酸的浓度较小时 ,峰位随浓度的增大表现为向低能移动 ;而当HF酸的浓度较大时 ,峰位随浓度的增大则表现为移向高能。多孔硅在空气中自然氧化 ,其发光峰位发生蓝移 ,而发射强度随放置时间的延长而降低。

Many experimental results and theoretical analysis diverge mostly because different preparation conditions can seriously affect on PL properties of porous silicon. Specimens of porous silicon were prepared under different conditions by double cell positive pole oxidizing method and their photoluminescence properties were analyzed systematically. Firstly, specimens were prepared in the same solution concentration ( V (HF)∶ V (C 2H 5OH)=1∶1) and erosion time (20 min) but under different oxidizing current density. Secondly, specimens were prepared in the same solution concentration ( V (HF)∶ V (C 2H 5OH)=1∶1) and current density (3 mA/cm 2) but for different erosion time. Thirdly, specimens were prepared in the same current density (3 mA/cm 2) and erosion time (20 min) but with different solution concentration. And then photoluminescence spectra of these specimens were measured at room temperature. Fourthly, photoluminescence spectra of the specimen, which prepared under the conditions of solution concentration ( V (HF)∶ V (C 2H 5OH)=1∶1) and current density (3 mA/cm 2) and erosion time (20 min), were measured respectively at room temperature after it had been lain in the air for three days, sixteen days and thirty days. Results suggest that, with the increasing of the current density, erosion time and the aging time, the peaks of PL shift to the blue, and the intensity of peaks is enhanced. But excessive current density and erosion time would cause the decrease of PL intensity. As for the solution concentration, peaks shift to the red when solution concentration is less than 1∶1 but shift to the blue when solution concentration is greater than 1∶1 with the increase of solution concentration. Above phenomena can be interpreted by quantum confinement model and light center model, as well as the action of Si-H bonding and other defects. In the process of porous silicon photoluminescence, peak shift and intensity change by current carrier limitation and surface passivation action. Increasing current density can produce more pits during initial stages of erosion, and can enhance hole energy in bulk silicon, and it is favorable for F -to go through potential barrier located at Si/HF interface to silicon surface, therefore quantum wire produced at silicon substrate can become thinner. To prolong erosion time can make quantum wire thinner too. The influence of solution concentration is more complex. The influence of aging time on peak position and intensity is obvious, and show that porous silicon quality is not steady.