Person:

Gordon, Roy

Enhancement-mode p-channel metal-oxide-semiconductor field-effect transistor (MOSFET) on germanium-on-insulator substrate is fabricated with atomic-layer-deposited (ALD) (LaLuO_3) as gate dielectric. Significant improvement in both on-state current and effective hole mobility has been observed for devices with thermal (GeO_2) passivation. The negative threshold voltage ((V_T)) shift in devices with (GeO_2) interfacial layer (IL) further demonstrates the effectiveness of surface passivation. Results from low temperature mobility characterization show that phonon scattering is the dominant scattering mechanism at a large inversion charge, indicating good interface quality. The combination of higher-k (LaLuO_3) and ultrathin (GeO_2) IL is a promising solution to the tradeoff between the aggressive equivalent oxide thickness scaling and good interface quality.

The growth of of metallic copper by atomic layer deposition (ALD) using copper(I) di-sec-butylacetamidinate (([Cu(^sBu-amd)]_2)) and molecular hydrogen ((H_2)) on (SiO_2/Si) surfaces has been studied. The mechanisms for the initial surface reaction and chemical bonding evolutions with each ALD cycle are inferred from in situ Fourier transform infrared spectroscopy (FTIR) data. Spectroscopic evidence for Cu agglomeration on (SiO_2) is presented involving the intensity variations of the (SiO_2) LO/TO phonon modes after chemical reaction with the Cu precursor and after the (H_2) precursor cycle. These intensity variations are observed over the first 20 ALD cycles at 185°C.

Zinc oxysulfide, Zn(O,S), films grown by atomic layer deposition were annealed in oxygen to adjust the carrier concentration. The electron carrier concentration of Zn(O,S) can be reduced by several orders of magnitude from (10^{19}) to (10^{15} cm^{−3}) by post-deposition annealing in oxygen at temperatures from 200 °C to 290 °C. In the case of Zn(O,S) with S/Zn = 0.37, despite the considerable change in the electron carrier concentration, the bandgap energy decreased by only ∼0.1 eV, and the crystallinity did not change much after annealing. The oxygen/zinc ratio increased by 0.05 after annealing, but the stoichiometry remained uniform throughout the film.

Thin film solar cells made from earth-abundant, non-toxic materials are needed to replace the current technology that uses (Cu(In,Ga)(S,Se)2) and (CdTe), which contain scarce and toxic elements. One promising candidate absorber material is tin monosulfide ((SnS)). In this report, pure, stoichiometric, single-phase SnS films were obtained by atomic layer deposition (ALD) using the reaction of (bis(N,N′-diisopropylacetamidinato)tin(II)) ([Sn(MeC(N-^{i}Pr){2})_{2}]) and hydrogen sulfide ((H_2 S)) at low temperatures (100 to 200 (°C)). The direct optical band gap of SnS is around 1.3 eV and strong optical absorption ((\alpha > 10^4 cm^{−1})) is observed throughout the visible and near-infrared spectral regions. The films are p-type semiconductors with carrier concentration on the order of (10^{16} cm^{−3}) and hole mobility (0.82–15.3cm^{2}V^{−1}s^{−1}) in the plane of the films. The electrical properties are anisotropic, with three times higher mobility in the direction through the film, compared to the in-plane direction.

Lanthanum-based ternary oxide (La_xM_{2−x}O_3) (M = Sc, Lu, or Y) films were deposited on HF-last Si substrates by atomic layer deposition. Both (LaScO_3) and (LaLuO_3) films are amorphous while the as-deposited (La_xY_{2−x}O_3) films form a polycrystalline layer/amorphous layer structure on Si. Transmission electron microscopy and electrical analysis show the absence of interfacial layers. The dielectric constants for (LaScO_3), (LaLuO_3), and (La_{1.23}Y_{0.77}O_3) films are (\sim 23), (28 \pm 1), and (17 \pm 1.3), respectively, with leakage current density up to 6 orders of magnitude lower than that of thermal (SiO_2) with the same effective oxide thickness. Conformal coating thickness is demonstrated on holes with aspect ratio (\sim 80:1).

Thin-film solar cells consisting of earth-abundant and non-toxic materials were made from pulsed chemical vapor deposition (pulsed-CVD) of SnS as the p-type absorber layer and atomic layer deposition (ALD) of Zn(O,S) as the n-type buffer layer. The effects of deposition temperature and annealing conditions of the SnS absorber layer were studied for solar cells with a structure of Mo/SnS/Zn(O,S)/ZnO/ITO. Solar cells were further optimized by varying the stoichiometry of Zn(O,S) and the annealing conditions of SnS. Post-deposition annealing in pure hydrogen sulfide improved crystallinity and increased the carrier mobility by one order of magnitude, and a power conversion efficiency up to 2.9% was achieved.

Abstract We have prepared two new CaII amidinates, which comprise a new class of ALD precursors. The syntheses proceed by a direct reaction between Ca metal and the amidine ligands in the presence of ammonia. Bis(N,N′‐diisopropylformamidinato)calcium(II) (1) and bis(N,N′‐diisopropylacetamidinato)calcium(II) (2) adopt dimeric structures in solution and in the solid state. X‐ray crystallography revealed asymmetry in one of the bridging ligands to afford the structure [(η2‐L)Ca(μ‐η2:η2‐L)(μ‐η2:η1‐L)Ca(η2‐L)]. These amidinate complexes showed unprecedentedly high volatility as compared to the widely employed and commercially available CaII precursor, [Ca3(tmhd)6]. In CaS ALD with 1 and H2S, the ALD window was approximately two times wider and lower in temperature by about 150 °C than previously reported with [Ca3(tmhd)6] and H2S. Complexes 1 and 2, with their excellent volatility and thermal stability (up to at least 350 °C), are the first homoleptic CaII amidinates suitable for use as ALD precursors.

Ruthenium thin films were deposited by atomic layer deposition from bis(N,N’-di-tert-butylacetamidinato)ruthenium(II) dicarbonyl and O2. Highly conductive, dense and pure thin films can be deposited when oxygen exposure EO approaches a certain threshold ( Emax ). When EO > Emax, the film peels off due to the recombinative desorption of O2 at the film/substrate interface. Analysis by an atomic probe microscope shows that the crystallites are nearly free of carbon impurity (<0.1 at.%), while a low level of carbon (<0.5 at.%) is segregated near the grain boundaries. The atom probe microscope also shows that a small amount of O impurity (0.3 at.%) is distributed uniformly between the crystallites and the grain boundaries.

Indium oxide is a major component of many technologically important thin films, most notably the transparent conductor indium tin oxide (ITO). Despite being pyrophoric, homoleptic indium(III) alkyls do not allow atomic layer deposition (ALD) of In2O3 using water as a co‐precursor at substrate temperatures below 200 °C. Several alternative indium sources have been developed, but none allows ALD at lower temperatures except in the presence of oxidants such as O2 or O3, which are not compatible with some substrates or alloying processes. We have synthesized a new indium precursor, tris(N,N′‐diisopropylformamidinato)indium(III), compound 1, which allows ALD of pure, carbon‐free In2O3 films using H2O as the only co‐reactant, on substrates in the temperature range 150–275 °C. In contrast, replacing just the H of the anionic iPrNC(H)NiPr ligand with a methyl group (affording the known tris(N,N′‐diisopropylacetamidinato)indium(III), compound 2) results in a considerably higher and narrower ALD window in the analogous reaction with H2O (225–300 °C). Kinetic studies demonstrate that a higher rate of surface reactions in both parts of the ALD cycle gives rise to this difference in the ALD windows.

Better than Elmer's glue: Three necessary conditions for enhancement of solid interfacial interactions guide materials design to create strong, stable composites for interfacial adhesion. Ab initio molecular dynamics simulations were used to study copper adhesion on TaN(111) surfaces with a variety of intervening metals to enhance adhesion (see picture). The predicted adhesion phenomena agree well with experimental observations.