多孔硅的光致发光和红外吸收光谱研究

用电化学腐蚀法制备出多孔硅系列样品.室温下具有明亮可见的光致发光.增大电解电流或延长腐蚀时间,发光光谱明显地“蓝移”;提高样品测量温度,发光光谱也明显地“蓝移”。红外吸收光谱表明多孔硅中除了硅丝骨架以外,还含有H、F及O等元素,随着腐蚀时间的增加,F和O原子的相对含量增加.实验结果表明,多孔硅在可见光区的发光现象是一种量子尺寸效应.

PHOTOLUMINESCENCE AND INFRARED SPECTRO-SCOPY OF POROUS SILICON

Porous silicon samples were prepared by electrochemical etching in HF-C2H5OH solution. Polished n type and p type (111) Si wafers with resistivities of 40-60Ω·cm, and 8-10Ω·cm, respectively, were used as substrates. A contact was made to the back of the wafer, which served as the anode and Pt as cathode. The typical etching current was 1-10mA.The samples show intense red colour luminescence excited by UV light or 488nm lino from Ar ion laser at room temperature. The PL band is rather broad with the full width at half maximum of about 0.31eV. The peak wavelength shifts from 770nm to 730nm as the etching time increases from one hour to 6 hours, keeping the etching current at 2mA. While increasing the current to 10mA, the peak position further shifts to 670nm. Such a large blue shift has also been observed when increasing measurement temperature. Infrared spectra show that there are Si-H, bond vibration absorptions at 2080-2100cm-1. 850-900cm-1 and 640cm-1 corresponding to the stretching, bending and wagging modes, respectively. Besides Si-Hn bondings in porous Si, Si-F and Si-O bondings at 830cm-1 and 1070-1120cm-1, respectively, have also observed and the relative content of F and O atoms increases with the etching current.The structure of porous silicon consists of nanometre size and micrometer deep silicon columns produced by electrochemical ething. The visible luminescence in porous silicon is attributed to the radiative recombination of excitons confined at the quantum wires. The incorporation of H and F atoms in the sampler is considered as the terminatinators of the dangling bonds at the surfaces of the silicon wires, and may play an important role in keeping a high intense visible PL. Extending etching time or increasing oxygen content would thin the quantum wire, resulting in the blue shift of the PL spectra.