Electrical characteristics of Al/SiO sub(2)/n-Si tunnel diodes with an oxide layer grown by rapid thermal oxidation

Ultrathin oxide layers, 2-5 nm thick, have been grown on (100) n-Si by Rapid Thermal Oxidation (RTO) at 900 degree C. RTO is an effective method to control the oxide thickness in this range to within 10%. The direct tunnelling through these ultrathin layers is examined with current voltage and impedance measurements on Al/SiO sub(2)/n-Si structures with an oxide layer thickness between 2 and 4 nm. After the determination of the surface potential vs bias relation and the oxide layer capacitance from the capacitance-voltage measurements, a quantitative analysis of the current-voltage characteristic based on electron tunnelling from a degenerate accumulation layer through the SiO sub(2) barrier into the metal is made. A very good agreement with the theory is obtained assuming a simple trapezoidal tunnel barrier for the SiO sub(2), from which the tunnel barrier height and the electron effective mass in the SiO sub(2) bandgap are derived. The density of interface traps at the Si/SiO sub(2) interface is determined using the conductance method. Only a very small increase of interface trap density with decreasing oxide layer thickness is found. The very high density of interface traps (more than 3 x 10 super(12) cm super(-2) eV super(-1)) can be reduced to the 10 super(10) cm super(-2) eV super(-1) level by application of a conventional Post Metallization Anneal (PMA).