Estimation of Schottky contacts to porous Si by photoacoustic spectroscopy

The photoacoustic (PA) spectra of porous Si (PS) were measured using a microphone under various surface treatments such as vibration during anodisation, vibration during rinsing, and acid surface treatment before contact deposition. The Fourier transform infrared (FTIR) spectra were also compared for the estimation of surface conditions. To obtain good contacts for electroluminescence (EL) devices, where a large injection current during operation is required, the vibration during rinsing in distilled (DI) water and hydrochloric (HCl) acid surface treatment are important. The PA signals increase with such vibration because of the enhancement of the pressure effects in pores of PS. Moreover, the decrease in PA signals caused by the surface change of pores can be also observed with the surface treatments. As the good contacts are obtained both by the vibration and surface treatments, the surface states in the pores seem to be important for the contacts to PS. This process can be monitored by PA spectroscopy in a noncontact manner because the PA signals from the PS are enhanced in the pores by the pressure effects, and PA spectroscopy can be sensitive to the change in surface of pores of PS.