Influence of thickness and porous structure of SiC layers on the electrical properties of Pt/SiC-pSi and Pd/SiC-pSi Schottky diodes for gas sensing purposes

Abstract

Abstract The aim of this work was to study the influence of the thickness and porous structure of silicon carbide (PSC) layers on the electrical properties of Schottky diodes for gas sensing purposes by using a platinum (Pt) or a palladium (Pd) layer deposited on non-porous silicon carbide (SiC) and porous SiC (PSC) layers. The Schottky diodes were used for the first time for H2 and hydrocarbon (C2H6) gas sensing. The non-porous and porous SiC layers were realized on a p-type silicon (Si(1 0 0)) substrate by pulsed laser deposition using a KrF laser (248 nm) and thermal deposition of a thin Pt and Pd layer. The porous structure of the SiC layer deposited was developed by an electrochemical (anodization) method. The properties of the porous SiC layers formed by this method were investigated by scanning electron microscopy (SEM). The electrical measurements were made at room temperature (295 K) in an air ambience using a cryostat chamber. The effect of the porous surface structure and the thickness of the SiC layer was investigated by evaluating electrical parameters such as the ideality factor (n), barrier height (ϕBp) and series resistance (Rs). The thickness of the porous layer significantly affects the electrical properties of the Schottky diodes. 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. For a thin SiC layer (0.16 μm) n was around 1.293 with a barrier height 0.847 eV, while for a thick layer (1.6 μm), n and ϕBp were 1.110 and 0.812 eV, respectively, for both Pt/SiC-pSi and Pd/SiC-pSi. The low value of series resistance obtained using Cheung's method clearly indicated the high performance of the Schottky diode for large SiC layer thickness. This effect showed the uniformity of the SiC layer. C–V analysis revealed a decrease in the capacitance with increasing voltage. This decrease was less for a thin SiC layer (0.16 μm) than a thick SiC layer (1.6 μm), clearly indicating the role of the SiC thickness in the determining sensor capacitance values. Finally, high sensitivity (ΔI/I = 90%) and selectivity of the sensors were reached at low voltages below 1 V, by using the PSC layer with catalytic metals of Pt and Pd.