V.E. Lashkaryov Institute of Semiconductor Physics NAS of Ukraine
National Academy of Sciences of Ukraine


Technology  for  porous  silicon  production

№3 The department of photoelectric phenomena
B.M. Bulakh, L.Yu. Khomenkova

Importance and effectiveness of the development. During the last years a significant interest to porous silicon was caused by the discovery of bright luminescence in visible spectral range at room temperature. This discovery gave the possibility to create optoelectronic devices based on cheap silicon technology. It also stimulated the intensive investigations of light emission properties of this material as well as the development of different microelectronic devices such as light emitting diodes, photo-converters, chemical and biosensors based on it. Since operation of all mentioned devices is based on the phenomenon of photoluminescence, one of the actual tasks is to increase an external efficiency of porous silicon luminescence.

Short description of the development. Developed technology allows to produce the layers of porous silicon emitting light in the visible spectral range. Preparation regimes and chemical composition of electrolyte depend on type and conductivity of silicon. Production of the layers includes also an additional treatment (oxidation), which leads to the increase of luminescence intensity as well as to stabilization of light emission characteristics of porous silicon.

The main technical characteristics and parameters. Developed technology allows to produce both nanoporous layers with pores and crystallites of several nanometers of sizes, and macroporous layers with pores of several micrometers (Fig.1,a). In the last case the sizes of crystallites change from several nanometers to hundred nanometers (Fig.1,b). The room temperature emission spectrum of the layers is dominated by broad unstructured band with peak position located in the range from 600 nm to 780 nm (Fig.2) in dependence on preparation regimes. The external quantum yield is about 15-20%.

020 2 020 3
a) b)

Fig.1. The images of the surface of porous layers obtained with scanning electron microcopy (a) and atomic force microscopy (b). The layers are prepared at current density and etching time of  jA=25 мA/см2 and  tA=10 min, respectively. Chemical composition of electrolyte is HF:H2O:C2H5OH=1:2:1.

020 4 Fig.2. Photoluminescence spectra of porous layers prepared at different current densities jа= 25 (curve 1), 50 (curve  2) and 100 mА/сm2 (curve  3); and etching time tа=10min. Chemical composition of electrolyte is HF:H2O:C2H5OH=1:2:1. Excitation light wavelength is 450 nm.

The main advantages in comparison with existing analogues.

The method of preparation of light-emitting porous silicon layers              

The authors of development External quantum efficiency of porous silicon layers, %
The Secretary of State for Defense in Her Britannic Majesty's Government, Great Britain, 1994 (experimental setup) 1-8 %
Nippon Steel Corporation, Japan, 1994; (experimental setup) (US patent 528507, publication date 08.02.1994) 10 %
T. Shevchenko National University, Ukraine, 2000 (laboratory setup) 12 %
V. Lashkaryov Institute of Semiconductor Physics at NAS of Ukraine, Ukraine, 1998 (laboratory setup) 20 %

Area of application. Developed technology can be used for fabrication of different microelectronic devices such as light-emitting diodes, photodetectors and converters, as well as for gas-, chemical and bio-sensors.