Infrared ellipsometry characterization of porous silicon bragg reflectors

We investigate porous silicon Bragg reflectors in a nondestructive manner using variable angle-of-incidence infrared spectroscopic ellipsometry. In addition to the thickness, volume porosity, inhomogeneity, and optical anisotropy, properties of the solid content of the porous material are investigated in terms of dielectric function and surface chemistry. The material was found to have positive birefringence. The high sensitivity of the technique is employed to detect and identify infrared resonant absorptions related to different Si-H as well as Si-O-Si vibrational modes. The average electrical resistivity of the solid content of the porous material is determined to be 0.03 Omega cm, which is larger than the corresponding bulk value of 0.019 Omega cm. Furthermore the average carrier concentration in the porous material shows a decrease from 6.2 x 10(18) cm(-3) to 4 x 10(18) cm(-3).