In situ photoluminescence characterization of porous silicon formation

Abstract

P-type silicon wafers (100) with resistivities of 0.1-0.9 Ω cm were electrochemically etched in 2% HF solution at 0.7077 mA cm-2. The photoluminescence (PL) spectra for each wafer were monitored in situ using a low power 325 nm (He/Cd Laser) source and detected with a charged coupled detector (CCD) system. Three bands at 540 nm, 570 nm, and 612 nm were observed in the photoluminescence spectra. The band intensities grew with time until about 15 min of etching had occurred. The growth of PL intensities generally correlates with the surface morphologies and increase in roughness found from ex situ atomic force microscopy (AFM) of similarly etched samples. Ex situ PL characterization was also performed for the AFM analyzed samples. While the time profiles of the ex situ and in situ PL intensities were about the same, the ex situ peak intensities at longer wavelengths continued to increase after 15 min. The results of energy dispersive X-ray analysis (EDX) suggested that this may be due to the effect of oxygen in the air exposed samples.