Characterization of band offset in α-(AlxGa1-x)2O3/ α-Ga2O3 heterostructures
Gallium Oxide is a promising material for power device applications. We focused on corundum structured gallium oxide (α-Ga<sub>2</sub>O<sub>3</sub>) and α-(Al<sub>x</sub>Ga<sub>1-x</sub>)<sub>2</sub>O<sub>3</sub>/ α-Ga<sub>2</sub>O<sub>3</sub> heterostructure devices. We prepared α-(Al<sub>x</sub>Ga<sub>1-x</sub>)<sub>2</sub>O<sub>3</sub> alloy and these laminate structures on c-plane sapphire substrates. The band offset of the α-Ga<sub>2</sub>O<sub>3</sub>/α-(Al<sub>x</sub>Ga<sub>1-x</sub>)<sub>2</sub>O<sub>3</sub> heterostructure was measured by X-ray photoelectron spectroscopy (XPS). The band alignment was estimated to be type I with very narrow valence-band offset energy.
Quasiparticle band offset at the (001) interface and band gaps in ultrathin superlattices of GaAs-AlAs heterojunctions.
A newly developed first-principles quasiparticle theory is used to calculate the band offset at the (001) interface and band gaps in 1{times}1 and 2{times}2 superlattices of GaAs-AlAs heterojunctions. We find a sizable many-body contribution to the valence-band offset which is dominated by the many-body corrections to bulk GaAs and AlAs quasiparticle energies. The resultant offset {Delta}{ital E}{sub {ital v}}=0.53{plus minus}0.05 eV is in good agreement with the recent experimental values of 0.50--0.56 eV. Our calculated direct band gaps for ultrathin superlattices are also in good agreement with experiment. The {ital X}{sub 1{ital c}}-derived state at point {bar {Gamma}}, is however, above the {Gamma}{sub 1{ital c}}-derived state for both the 1{times}1 and 2{times}2 lattices, contrary to results obtained under the virtual-crystal approximation (a limiting case for the Kronig-Penny model) and some previous local-density-approximation (corrected) calculations. The differences are explained in terms of atomic-scale localizations and many-body effects. Oscillator strengths and the effects of disorder on the spectra are discussed.
Resonant Auger decay study of C1s -> pi* core-excited OCS
The present work aims at characterizing short-lived C1s((-1)) pi*((1)) core-excited states of the OCS molecule based on the analysis of the vibrational fine structure and lineshape profiles of the high-resolution resonant Auger decay spectra recorded at the excitation energies along the C1s -> pi* resonance in the binding energy region 15-19eV. Very different behavior in terms of lineshape and resonant enhancement is observed for the (A) over tilde, (B) over tilde and (C) over tilde final states. This is explained by (1) the variation in the C-O bond lengths for the states involved in the electronic relaxation and (2) different contributions in terms of Mulliken population to the molecular orbitals determining the electronic character of the corresponding states. Since the final-state geometries are known from a number of previous experiments and ab initio calculations, the geometry of the C1s((-1)) pi*((1)) intermediate states can be predicted in analogy with e.g. the N-2, CO2 and N2O molecules. (C) 2009 Elsevier B.V. All rights reserved. (Less)