Admittance and subthreshold characteristics of atomic-layer-deposition Al2O3 on In0.53Ga0.47As in surface and buried channel flatband metal-oxide-semiconductor field effect transistors

The admittances and subthreshold characteristics of capacitors and MOSFETs on buried and surface In0.53Ga0.47As channel flatband wafers, with a dielectric of Al2O3 deposited on In0.53Ga0.47As, are reported. The admittance characteristics of both wafers indicate the presence of defect states within the oxide, in common with a number of other oxides on In0.53Ga0.47As. The two wafers studied have not been hydrogen annealed, but do show some similar features to FGA treated oxides on n(+) substrates. We discuss how the possible presence of residual hydroxyl ions in as-grown Al2O3 may explain these similarities and also account for many of the changes in the properties of FGA treated n(+) samples. The issues around the comparison of subthreshold swing (SS) results and the impact of transistor design parameters on the energy portion of the defect state distribution affecting efficient device switching are discussed. The interface state model is applied to low source-drain voltage SS data to extract an effective interface state density (D-it) that includes interface and oxide traps. The logarithmic gate voltage sweep rate dependence of the SS D-it is used to extract an oxide trap density (D-ot) and a simple method is used to estimate the Fermi level position within the band gap, E-t. The Al2O3 D-it(E-t) and D-ot(E-t) distributions are found to be similar to each other and to the results of our analysis of Gd0.25Ga0.15O0.6/Ga2O3 and HfO2/Al2O3 on In0.53Ga0.47As, adding weight to the suggestion of there being a common defect state distribution and perhaps a common cause of defects states for a number of oxides on In0.53Ga0.47As. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4720940]