Paper EM+SS-WeA7
Fermi-level Unpinning of HfO₂/In_0.53Ga_0.47As Gate Stacks using Hydrogen Anneals

Wednesday, October 20, 2010, 4:00 pm, Room Dona Ana

Compound (III-V) semiconductors are currently being investigated to replace Si as channel material in metal oxide semiconductor field effect transistors. A significant challenge is the high trap density (D_it) at the dielectric/III-V semiconductor interface, causing Fermi level pinning. Recently, it has been reported that the D_it can be reduced by sulfur passivation and hydrogen annealing for Al₂O₃/In_0.53Ga_0.47As interfaces.

In this presentation, we will present our studies of the effect of forming gas anneals on the electrical properties of HfO₂/In_0.53Ga_0.47As metal oxide semiconductor capacitors . HfO₂ films with thicknesses between 9 and 18 nm were deposited in-situ on As-decapped n-type In_0.53Ga_0.47As channels by chemical beam deposition using hafnium tert-butoxide (HTB) as the source. Samples were post-deposition annealed in forming gas. For comparison samples annealed in nitrogen were also studied. Capacitance-voltage (CV) and conductance-voltage (GV) curves were measured at room temperature. The interface trap density D_it was quantified using both the Terman and the conductance methods. The conductance method showed that the D_it was reduced from 1.3Χ10¹³cm^-2eV^-1 to 8Χ10¹²cm^-2eV^-1 near midgap. The conductance peak shifted in frequency with a change in negative gate voltage, consistent with an unpinned Fermi level. The 1 MHz CV curve reached the calculated minimum capacitance value, indicating Fermi level unpinning. The nitrogen annealed control sample did not reach the minimum capacitance and the conductance peak shift at negative bias was moderate, indicating Fermi level pinning at midgap. We will also present comparisons of the extracted band bending for both nitrogen and forming gas annealed stacks and discuss the mechanisms by which forming gas anneals can reduce the midgap D_it.