Fermi Level Tuning by Nanograting Depth in Si Substrates

Nanograting (NG) is a new method for externally doping the surface of Si substrates only by creating nano-size indents. This geometry-induced doping (G-doping) occurs due to quantum effects ruling the patterned region. Our experimental investigations verified that the Fermi level difference at the patterned region depends on the depth of NG indents and, consequently, affects the electronic, magnetic, and optical properties of the NG region. Here, several Si substrates were patterned with different NG depths using laser interference lithography and a consecutive series of reactive ion etching. Four NG regions with 10, 20, 30, and 40 nm were patterned on p-type, n-type, p+ type, and n+ type Si substrates, and 8 samples were cut separately for statistical analysis of the results. The Fermi level difference of these NG regions was characterized by Kelvin probe showing that the Fermi level difference raised for NG-regions with maximum increase for indents of 10 nm depth but declined by increasing the NG depth to 40 nm both in p-type and n-type substrates. Highest decline observed for p-type substrates but negligible increase in n+ type and p+ type substrates. XPS and SEM analyses performed to verify the surface quality and microstructure of NG-junctions.