Electroluminescence (EL) from photo-chemically etched silicon

Abstract

Visible luminescence from Si-based materials has been investigated to develop new opto-electronic devices on a Si wafer. In this report, we propose a photo-chemical etching method in order to form a luminescent layer on a Si wafer. A comparison between electroluminescence (EL) and photoluminescence (PL) from the photo-chemically etched silicon is discussed. In the photo-chemical etching method, a Si wafer (100) with resisitivity of 35–45 or 0.22–0.38 ohm-cm is set at the bottom of a vessel filled with an etchant (HF+H 2O 2), and a He–Ne laser (633 nm, 18.4mW/cm 2) is irradiated onto the surface for 30 min. An Au thin film (thickness 5 nm) is deposited onto the the etched layer, and a Au–Sb (1 wt%) film is deposited on the reverse side of the Si wafer to form ohmic contacts. The EL from the etched layer is observed by applying a voltage to the electrodes(−30∼+30V). PL from the etched layer is measured by He–Cd laser excitation (325 nm). As a result, it is clear that the peak wavelength of EL at forward bias coincides with a peak wavelength of PL. EL spectra at backward bias can be fitted by two gaussian functions, and one of them coincides with a peak wavelength of PL. In addition, the EL from the photo-chemically etched silicon can be explained schematically by an electrical circuit model.