Optical and Electrical Characterization of Atomic Layer Deposited (ALD) HfO2/p-GaAs MOS capacitors

The HfO2/p-GaAs metal-oxide-semiconductor (MOS) structures have been fabricated by developing and simulating an optimized process recipe. The optical dielectric constants and refractive indices of atomic-layer-deposited (ALD) HfO2 films and the GaAs substrate are extracted from spectroscopic ellipsometer (SE) measurements. The quality of interface and that of the ALD HfO2 films is investigated by analyzing capacitance-voltage (C-V) and conductance-voltage (G-V) data. Simulations of C-V and G-V data have also been performed for a similar process recipe to comprehensively understand the electrical quality of the dielectric layer. The optical dielectric constants for HfO2 and GaAs layers are obtained to be 4.5-3.6 and 10-25, respectively, while their refractive indices are obtained to be 2.12-1.89 and 3-5.2, respectively. A frequency dispersion of the C-V graphs is observed indicating the presence of a Ga2O3 interfacial layer which has been confirmed from the device simulation. A flat band voltage shift of - (0.68-1.05) eV and interface state density of (5x10(11) -1 x 10(12)) cm(-2) eV(-1) are obtained.