Effect of thickness and porous structure of SiC layers on the spectral response of the Pd/SiC–pSi Schottky photodiodes

Abstract

In this work, we study the effect of the thickness and porous structure of silicon carbide (PSC) layers on the electrical properties of Schottky photodiodes by using a palladium (Pd) layer deposited on non-porous silicon carbide (SiC) and porous-SiC (PSC) layers. The non-porous and porous-SiC layers were realized on a p-type silicon (Si(100)) substrate by pulsed laser deposition using a KrF laser (248nm) and thermal deposition of a thin Pd layer. The porous structure of the SiC layer deposited was developed by an electrochemical (anodization) method. The electrical measurements were made at room temperature (295K) in an air ambience. The effect of the porous surface structure and the thickness of the SiC layer were investigated by evaluating electrical parameters such as the ideality factor (n) and barrier height (ϕBp). The thickness of the porous layer significantly affects the electrical properties of the Schottky photodiodes. Analysis of current–voltage (I–V) characteristics showed that the forward current might be described by a classical thermal emission theory. The ideality factor determined by the I–V characteristics was found to be dependent on the SiC thickness a value For a thin SiC layer (0.16μm) n was around 1.325 with a barrier height 0.798eV, while for a thick layer (1.6μm), n and ϕBp were 1.026 and 0.890eV, respectively for Pd/SiC–pSi. These results indicate Schottky photodiodes with high performance are obtained for thicker SiC layer and for thin layer of PSC. This effect showed the uniformity of the SiC layer. In the same case the ideality factor (n) decreases for Pd/PSC–pSi(100) for low SiC thickness by report of Pd/PSC–pSi(100) Schottky photodiodes, but for Pd/PSC–pSi(100) n increase for large SiC thickness layer. We notice that the barrier height (ϕBp) was reversely depend by report of ideality factor. A spectral response value of (SR) of 34mA/W at λ=400nm was measured for Pd/0.16μm SiC–pSi Schottky photodiode with low SiC thickness. On the other hand, a value of SR=0.14mA/W at λ=900nm was obtained when we used PSC layer (Pd/PSC–pSi(100)). A reverse behaviour occurs for thicker SiC layer. Finally, it was found that the thickness and surface porous structure have strong effect on sensitivity.