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(a) Quantum yield of electron IPE from Si as a function of photon energy measured on Si/Al2O3/Au samples with an as-deposited 12-nm thick amorphous ALD Al2O3 layer (open symbols), with polycrystalline Al2O3 (same samples) obtained by annealing at 1000 °C (filled symbols), and with a 8-nm thick epitaxial film of (111) γ-Al2O3 (gray symbols). Vertical lines indicate energies of direct optical transitions in the Si substrate crystal acting as the source of photoelectrons;(b) Schottky plot of the field dependent electron IPE thresholds as measured on samples with different types of insulating Al2O3. Lines illustrate linear fits used to infer the zero-field energy barrier between the top of the Si VB and the bottom of the alumina CB.
Logarithmic (a) and Fowler (b) plots of the quantum yield of electron IPE from TiNx into Al2O3 as measured on Si/Al2O3(12 nm)/TiNx(10 nm) and Si/TiNx(10 nm)/Al2O3(17 nm)/TiNx(10 nm) samples with amorphous and polycrystalline γ-Al2O3 insulating layers. Curves measured under positive and negative bias correspond to electron IPE from the bottom and top TiNx electrodes, respectively. The insert in panel (b) shows a schematic of the observed electron transitions.
Schematic of the band offset variation in Si/Al2O3/TiNx structures caused by the transition from a-Al2O3 to γ-Al2O3. The VB offsets are calculated using the experimental values of the bandgap width in a-Al2O3 (6.2eV, Ref. 9) and γ-Al2O3 (8.7 eV, Ref. 7) and the electron IPE barrier heights determined in the present work.
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