Visible luminescence from photo-chemically etched silicon

Abstract

A new photo-chemical etching method using H 2O 2 as an oxidant was proposed to form a luminescence layer on a Si wafer. A single crystalline n-type Si wafer (100) having resisitivity of 35–45 Ω cm was photo-chemically etched in a mixture of HF and H 2O 2 (HF:H 2O 2=6:1), and He–Ne laser (633 nm) was irradiated onto the wafer surface through the solution for photo-chemical reaction. Luminescence from photo-chemically etched layers was measured by photoluminescence (PL) using a He-Cd laser for excitation. It was found that the layer etched for 30 min shows strong yellow luminescence with a peak at 637 nm, while the layer etched for 5 min shows red luminescence with a peak at 695 nm. It is also confirmed that the etched layer exhibiting various color can be patterned. Blue luminescence (420 nm) can be obtained by dipping the layer etched for 30 min in a solution of ethanol and H 2O (ethanol:H 2O=1:1 for volume) for 148 h. The absorption peak of Si-O-Si is observed in the blue-luminescence layer by Fourier transform infrared (FTIR) absorption spectroscopy, indicating that the blue-luminescence is due to the oxidation of the photo-chemically etched layer.