Effects of Growth Conditions on Structural and Optical Properties of Porous GaAs Layers

Porous GaAs was prepared using electrochemical anodization technique of a cristalline GaAs wafer in hydrofluoridric (HF) acid based-solution at different manufacturing conditions. The physical properties of porous GaAs are mainly determined by the shape, diameter of pores, porosity, and the thickness of deposited porous layers. Depending on the etching parameters such as current density, HF concentration or substrate doping type and level, the physical properties of porous GaAs can be varied. In the present work, we investigate the structural and optical properties of porous GaAs etched at different current densities. The PL spectra of the porous layers reveal the presence of infrared and visible peaks observed at 1.42 and 1.80 eV respectively. The infrared PL peak is associated with the band gap edge of bulk GaAs and the visible PL band is due to quantum confined transitions in GaAs crystallites, induced by electrochemical etching. Both peak wavelengths and intensities of PL peaks vary as versus the treatment of samples. The refractive index and the extinction coefficient of the as-prepared GaAs have been determined in the 4001000 nm wavelength range using spectroscopic ellipsometry. These optical parameters are in agreement with the Bruggeman effective medium model. As has been found, the refractive index at 632 nm increases from 1.42 to 1.74 with increasing the film thickness from 52 to 154 nm and decreasing the porosity from 78 to 68 per cent.