[13a-A35-1~10] 13.9 Optical properties and light-emitting devices

▲ [13a-A35-10] Optical Absorption of Porous Silicon during Dissolution in HF Investigated by Photoconduction

〇Bernard Gelloz¹, Kazuki Ichimura², Eiichi Kondoh², Lianhua Jin² (1.Nagoya Univ., 2.Yamanashi Univ.)

Keywords:porous silicon, optical absorption, nanostructure

Porous silicon (PSi) formed by electrochemical etching of lightly-doped silicon substrates in hydrofluoric acid (HF) exhibits a sponge-like nano-structure. It has many potential applications in optoelectronics, photovoltaics, medicine and sensing. After PSi formation, further chemical dissolution in HF can be used to increase the porosity and enlarge the pores. The control of the porosity as a function of dissolution time is not easy, and is usually based on inspection studies. Here we show a method of monitoring of the dissolution based on the PSi optical absorption measured in-situ in HF by an easy to implement photoconduction technique. This technique was used previously to measure the PSi optical constants. We have studied the method with various types of PSi layers. Different porosities, thicknesses and HF concentrations were investigated. A model was developed to understand the evolution of the photocurrent and optical absorption coefficient as a function of time. Information on (i) the kinetic of the PSi dissolution, (ii) the optical absorption coefficient of PSi and (iii) the specific internal area of PSi as a function of porosity can be extracted. In some cases, the porosity-dependence of the refractive index of PSi can also be determined.