Luminescent characteristics of a novel porous silicon structure formed in a nonaqueous electrolyte

Abstract

Novel porous silicon layers which photoluminesce and electroluminesce in an aqueous solution have been formed by oxidation of (100) silicon in anhydrous acetonitrile-HF solutions. The novel porous structures consisted of large, noninterconnected pores, 1-2 pm diam, which grew normal to the surface. The pores were spaced 2-3 pm apart, and the length, which could be over 150 pm, was dependent on etch time and current density. Microporous structures (i.e., <lo0 nm), often associated with luminescence from porous silicon, were not detected by TEM, SEM, or infrared examination. The porous surface was hydride terminated, which was critical to the luminescence process. Since water and oxygen were not present during the formation of the porous structure and the pores were relatively large, neither silicon-oxygen species (e.g., siloxenes) nor quantum size structures, aIjpeared necessary for the generation visible luminescence from porous silicon.

Photoluminescence properties of porous silicon layers prepared by electrochemical etching in extremely dilute HF solutions

“…Thus it can be concluded that the formation of silicon oxides plays a major role in producing luminescent Si nanostructures in PSi layers. This hypothesis is supported further by the experimental results of Propst et al [30]. They used nonoxidative, anhydrous HF solutions to obtain PSi layers.…”

Morphological and optical characteristics of porous silicon produced by anodization process in HF-acetonitrile and HF-ethanol solutions

“…PL spectra corresponding to samples prepared in each solution with the same anodization conditions, current density (56.5 mA cm -2 ), anodization time (10 min) and resistivity [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] cm, are shown in Figure 3. PL spectrum for sample produced from HF-MeCN solution presented a blue shift peak that may depend on the pore depth and diameter.…”

“…Consequently, HF-ethanol has been used by most research groups as the standard electrolyte for PS formation process. After that, Propst et al 6 have reported the electrochemical oxidation of p-and n-type silicon in nonaqueous electrolyte of HF-MeCN and discussed their singular and large porous structure.…”

“…12,13 Also, for the resultant PS layer the structure is highly dependent on the experimental parameters, such as concentration of the HF acid, current density, anodization time, and also, the doping type associated to the carrier concentrations of the silicon wafer. 5,6,8,12 In addition, another parameter that affects the properties of the PS formed layer that has received little attention are the electrolyte additives. These additives on HF solution work as surfactants and play an important role increasing the mobility at the silicon surface.…”

“…Consequently, HF-ethanol has been used by most research groups as the standard electrolyte for PS formation process. After that, Propst et al 6 have reported the electrochemical oxidation of p-and n-type silicon in nonaqueous electrolyte of HF-MeCN and discussed their singular and large porous structure.Although PS layers were studied intensively, there are still questions about the dissolution chemistry of Si, and different mechanisms have been proposed. 7,8 In general, it is discussed and accepted in the literature that holes (h+) are required for both electropolishing and pores formation, where two hydrogen atoms are evolved for Morphological and Optical Characteristics of Porous Silicon Produced by Anodization Process J. Braz.…”