Electroluminescence and photovoltaic effects of anodically fabricated metal/porous Si/Si sandwich structures based on ntype ultravioletporous Si

No abstract

Planarity and control of the configuration of the cross-sectional area are important parameters to be considered for high density VLSI devices. The anodization process seems best to fulfill such conditions, but anisotropy (i.e., difference in vertical and lateral anodization rates), must be increased to obtain a competitive technique. In this work factors affecting the anisotropy of the aluminum anodization process were investigated. By varying the electrochemical process parameters, a degree of anisotropy of about 0.6 was obtained. The dimensions of the aluminum porous oxide were determined by scanning electron microscopy. At high forming voltages, the electric field across the barrier layer of the porous oxide cells were calculated and plotted.

We report the realization of a bright and stable electroluminescent Schottky diode based on aluminum-porous silicon junction. White light, visible in normal daylight, is emitted when a reverse bias is applied to the device, promoting the junction breakdown. The device has a fast (100 ns) rise time of the light emission. An excellent stability, tested over more than one month of continuous operation at a high bias level, is achieved by the complete encapsulation of the active porous silicon under a transparent alumina layer. The external power efficiency of light emission is 0.01%.

Porous silicon lattice deformation and its evolution with storage time are the main subjects of the present investigation. Transmission electron microscopy, x-ray diffractometry, and electronic paramagnetic resonance studies are reported. Silicon wafers of 0.01 Il cm resistivity n-type and (111) orientation were used as starting material. The porous silicon layers of 1.8 g/cm3 volume density were formed by anodization in 12% HF aqueous solution at current density of 20 mA/cm2. The as-grown porous silicon layers were stored in air atmosphere for a long time and were subjected to heattreatment in vacuum. Annealed porous silicon samples were stored again in air or in controlled atmosphere of hydrogen, nitrogen, or oxygen. The observed behavior of the porous silicon lattice parameter during storage in air and during thermal treatment allowed us to suppose that absorption/desorption processes, taking place at the inner developed porous silicon surface, are responsible for the lattice deformation.