LaScO 3 , deposited by pulsed laser deposition using ceramics targets of stoichiometric composition, were studied as alternative high-k gate dielectrics on ͑100͒ Si. Their physical characterization was done using Rutherford backscattering, spectroscopic ellipsometry, x-ray diffraction, and transmission electron microscopy on blanket layers deposited on ͑100͒ Si, and electrical characterization on capacitors. It is found that DyScO 3 and GdScO 3 preserve their amorphous phases up to 1000°C. Other encouraging properties for high k applications were demonstrated, including k-value ϳ22, almost no hysteresis or frequency dispersion in C-V curves, and leakage current reduction comparable to that of HfO 2 of the same equivalent oxide thickness.
The electron energy band alignment between (100)Si and several complex transition/rare earth (RE) metal oxides (LaScO 3 , GdScO 3 , DyScO 3 , and LaAlO 3 , all in amorphous form) is determined using a combination of internal photoemission and photoconductivity measurements. The band gap width is nearly the same in all the oxides ͑5.6-5.7 eV͒ yielding the conduction and valence band offsets at the Si/oxide interface of 2.0± 0.1 and 2.5± 0.1 eV, respectively. However, band-tail states are observed and these are associated with Jahn-Teller relaxation of transition metal and RE cations which splits their d* states.
Power conversion efficiency (PCE) of organic solar cells (OSCs) has crossed the 18% mark for OSCs, which are largely fabricated by spin‐coating, and the optimal photoactive thickness is limited to 100 nm. To increase reproducibility of results with industrial roll‐to‐roll (R2R) processing, slot‐die coating coupled with a ternary strategy for optimal performance of large‐area, thick OSCs is used. Based on miscibility differences, a highly crystalline molecule, BTR‐Cl, is incorporated, and the phase‐separation kinetics of the D18:Y6 film is regulated. BTR‐Cl provides an early liquid–liquid phase separation and early aggregation of Y6, which slightly improves the molecular crystallinity and vertical phase separation of the ternary blends, resulting in high PCEs of 17.2% and 15.5% for photoactive films with thicknesses of 110 and 300 nm, respectively. The ternary design strategy for large‐area and thick films is further used to fabricate high‐efficiency flexible devices, which promises reproducibility of the lab results from slot‐die coating to industrial R2R manufacturing.
Germanium combined with highdielectrics has recently been put forth by the semiconductor industry as potential replacement for planar silicon transistors, which are unlikely to accommodate the severe scaling requirements for sub-45-nm generations. Therefore, we have studied the atomic layer deposition ͑ALD͒ of HfO 2 high-dielectric layers on HF-cleaned Ge substrates. In this contribution, we describe the HfO 2 growth characteristics, HfO 2 bulk properties, and Ge interface. Substrate-enhanced HfO 2 growth occurs: the growth per cycle is larger in the first reaction cycles than the steady growth per cycle of 0.04 nm. The enhanced growth goes together with island growth, indicating that more than a monolayer coverage of HfO 2 is required for a closed film. A closed HfO 2 layer is achieved after depositing 4-5 HfO 2 monolayers, corresponding to about 25 ALD reaction cycles. Cross-sectional transmission electron microscopy images show that HfO 2 layers thinner than 3 nm are amorphous as deposited, while local epitaxial crystallization has occurred in thicker HfO 2 films. Other HfO 2 bulk properties are similar for Ge and Si substrates. According to this physical characterization study, HfO 2 can be used in Ge-based devices as a gate oxide with physical thickness scaled down to 1.6 nm.
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