Comparison of interfacial and electronic properties of annealed Pd/SiC and Pd/SiO2/SiC Schottky diode sensors

Abstract

Schottky diodes composed of palladium deposited on silicon carbide (Pd/SiC) detect hydrogen and hydrocarbon gases at elevated temperatures with high sensitivity. Previous examination of the properties of the Pd/SiC structure indicated that its forward current responded to the presence of hydrogen even after extended annealing at 425 °C. However, drift in the sensor properties suggested that stabilization of the diode structure was necessary. In this work, we examine the effects of placing a thin layer of silicon dioxide (SiO2) between the Pd and the SiC. Both Pd/SiC and Pd/SiO2/SiC diodes are annealed at 425 °C for 140 h and the electronic and interfacial properties of the annealed diodes are compared. The electronic properties and sensitivity to hydrogen of both diodes change significantly due to the annealing. Scanning electron microscopy and Auger electron spectroscopy indicate that the surface and interfacial properties of the diodes are very different. The Pd/SiC diode has a broad interface region with palladium silicides (PdxSi) distributed throughout the Pd. In contrast, the Pd/SiO2/SiC diode has a sharp interface with significantly less PdxSi formation. A silicon oxide (SiOx) layer has formed in the near surface region of the Pd which likely accounts for the relative insensitivity of the Pd/SiO2/SiC diode to hydrogen. The experimental data suggest that the mechanism for this SiOx formation is likely two-dimensional diffusion between the Pd and the surrounding SiC surface. While the thin SiO2 layer results in a sharp interface between the Pd and SiC, further stabilization of the diode structure is necessary for long term, high temperature sensor operation.

The growth of Pd thin films on a 6H-SiC(0001) substrate

“…Several studies concerning these properties have been reported in the literature [2][3][4][5]. Of particular interest is the study of the physical properties of its junctions with metals, since the reliability of the devices highly depends on the stability of their contacts [6][7][8][9][10][11][12]. In the present work, electron microscopy and atomic force microscopy (AFM) are used to clarify which are the experimental conditions for the growth of Pd thin films on 6H-SiC.…”

Palladium interaction with silicon carbide

“…After annealing at temperature higher than 1073 K some specimens presented Pd 3 Si and Pd 2 Si phases while other specimens presented only Pd 2 Si phase [22][23][24].…”

Palladium and ruthenium supported silver migration in 3C–silicon carbide

“…Pd content in the buffer, IPyC and outer pyrolytic carbon (OPyC) was significantly lower than that around the SiC layer indicating a trap or stabilization mechanism in this vicinity. From previous studies [1][2][3] and [8], it is known that Pd forms a silicide when heated in contact with SiC and this lowers the concentration of free Pd in the area and acts as a sink for Pd. Fig.…”