Formation of ohmic contact by pre-annealing of shallow nanopores in macroporous silicon and its characterization

Abstract

Abstract Macroporous silicon is a promising material for wide spectrum of electrical applications ranging from photonic devices, microsystems engineering, supercapacitors to biosensors. Fabrication of good quality ohmic contact on macroporous silicon is a prerequisite for its widespread use in electrical sensor applications but it is also challenging since shallow nanopores are always present within the macropores. This paper aims at the formation of low resistance and fairly ohmic contacts on p-type macroporous silicon with 1.5 μm pore diameter. Electrical contacts formed by vacuum evaporation of aluminium exhibit non-ohmic behaviour owing to the presence of the shallow nanoporous region formed on the surface of crystallites in macroporous silicon. To overcome this problem a controlled pre-annealing step at a temperature of 900 °C for 30 min leading to closure of shallow nanopores through coalescence of nanocrystallites of silicon due to grain growth has been carried out. The growth parameters are computed from the FESEM characteristics of the macroporous silicon preannealed at 900 °C for varying time. For optimally preannealed macroporous silicon the I – V characteristics of macroporous silicon has been found to exhibit fairly ohmic behaviour with vacuum evaporated aluminium. Detailed electrical characterization of vacuum evaporated contacts on both unannealed and preannealed macroporous silicon has been carried out using modified TLM technique. It has been found that the specific contact resistance is almost five times lower for the latter.