Rectifying and Schottky characteristics of a-SixGe1−xOy with metal contacts

Abstract

Metal–semiconductor contacts are a vital part of semiconductor devices as they can form a Schottky barrier or an Ohmic contact. The nature of the contact plays an important role in determining the electrical and physical characteristics of the device and hence is of paramount importance in the operation of the device. In the current work we report the design, fabrication, and current–voltage (I-V) characteristics of microbolometers, a type of infrared detector where the change in temperature changes the resistance of the sensing layer. Eight different types of microbolometers were fabricated using a-SixGe1−x or a-SixGe1−xOy sensing layers and Ti, Cr, Al, Au, Ni, or Ni0.80Cr0.20 metals contacts. It has been observed that bolometers with an a-Si0.15Ge0.85 (Si was lightly p-doped) sensing layer formed a Schottky contact with Ti, Au, Cr, and Al contact metals, while bolometers with a-Si0.15Ge0.85 (Si was heavily n-doped) sensing layers formed an Ohmic contact with Au. For microbolometers with a Si0.15Ge0.85O0.039 sensing layer, both Ni and Ni0.80Cr0.20 contact metals formed the Ohmic contact. For a-SixGe1−x and a-SixGe1−xOy microbolometers, Au and Ni0.80Cr0.20 were used as the absorber layers, respectively. The I–V characteristics of the microbolometers were analyzed with a thermionic emission model. A linear dependence on the Ge composition was approximated to find the effective Richardson constant. The theory predicts Richardson constants of 112 and 50 A/cm2K2 for Si and Ge, respectively. Barrier heights of all devices are calculated and the reasons for the formation of the Ohmic and Schottky contacts are discussed.