Study On Spectral Evolution Of Silicon Nanoporous Pillar Array In Solution Environment

Single crystal silicon is one of the most important basic materials in modern microelectronic technology and information industry,which plays an irreplaceable role in the field of microelectronics and integrated circuits.Silicon is abundant in earth crust,which is easy to prepare large-size single crystals at low cost,and the device integration process is mature.However,silicon is a narrow band gap indirect band gap semiconductor material(～1.12 e V),which can only emit near-infrared light(～1100 nm)at room temperature,and the luminous efficiency is very low.This characteristic seriously limits the application of silicon materials in the field of optoelectronic devices.The appearance of porous silicon(PS)and various silicon nanostructure materials greatly improves the luminous efficiency of silicon materials,and provides the possibility for the realization of silicon-based optoelectronic devices and their integration.In the previous research,our research group used hydrothermal etching of Single crystal silicon to prepare a silicon micron/nano composite structure-silicon nanoporous pillar array(Si-NPA).Si-NPA has the characteristics of triple hierarchy:the regular array structure composed of micron sized silicon pillars,the nano porous structure on the silicon pillars and the silicon nano grains forming the pore walls.The above structural characteristics make Si-NPA show good wide band light absorption characteristics and photoluminescence(PL)characteristics.Taking Si-NPA as the functional substrate,the principle devices such as light-emitting diodes,photodetectors and solar cells based on broadband gap compound semiconductor/Si-NPA heterojunction array were prepared successively by liquid phase method and chemical vapor deposition method,and excellent device performance was obtained.For the preparation of broadband gap compound heterojunction devices on Si-NPA substrate,the growth quality of compound semiconductor and the quality of heterojunction interface are very important to achieve good device performance.The surface condition of Si-NPA and its evolution law in various environments are the basis to control and optimize its preparation process.Based on the preparation of Si-NPA composite system by liquid phase method,this paper systematically studies the evolution of photoluminescence spectrum of freshly prepared Si-NPA immersed in a variety of solutions with time,and reveals the changes of surface morphology,structure and composition of Si-NPA in combination with SEM/EDS test,Raman spectrum and infrared absorption spectrum test of samples with different immersion time,so as to provide guidance for the preparation of high-quality and high-performance Si-NPA composite system in liquid phase.The main research results of this paper are as follows:(1)The time evolution of in-situ photoluminescence spectra of Si-NPA immersed in deionized water,hydrofluoric acid,mixed aqueous solution of hydrofluoric acid and ferric nitrate and absolute ethanol was studied,and the effects of these four solutions on the evolution of in-situ photoluminescence spectra of Si NPA were preliminarily clarified.(2)The samples immersed in different solutions for different times were taken out and dried,and then PL and SEM/EDS tests were carried out.The effects of these four solutions on the photoluminescence spectrum,surface morphology and main components of Si-NPA were obtained.(3)The samples immersed in different solutions for different times were tested by Raman spectrum and infrared absorption spectrum.It is demonstrated that the photoluminescence mechanism of porous silicon can not be completely supported by quantum confinement effect.The internal reason for the strong photoluminescence of the samples immersed in the mixed aqueous solution of hydrofluoric acid and ferric nitrate was revealed.The research results of this paper provide guidance for the preparation of high-quality and high-performance Si NPA composite system in liquid phase,and are of great significance to the research and application of Si-NPA and even porous silicon.