B. Holländer

Measurement of the band offsets between amorphous LaAlO3 and silicon

The conduction and valence band offsets between amorphous LaAlO3 and silicon have been determined from x-ray photoelectron spectroscopy measurements. These films, which are free of interfacial SiO2, were made by molecular-beam deposition. The band line-up is type I with measured band offsets of 1.8±0.2 eV for electrons and 3.2±0.1 eV for holes. The band offsets are independent of the doping concentration in the silicon substrate as well as the amorphous LaAlO3 film thickness. These amorphous LaAlO3 films have a bandgap of 6.2±0.1 eV.

Band engineering and growth of tensile strained Ge/(Si)GeSn heterostructures for tunnel field effect transistors

In this letter, we propose a heterostructure design for tunnel field effect transistors with two low direct bandgap group IV compounds, GeSn and highly tensely strained Ge in combination with ternary SiGeSn alloy. Electronic band calculations show that strained Ge, used as channel, grown on Ge 1−xSnx (x > 9%) buffer, as source, becomes a direct bandgap which significantly increases the tunneling probability. The SiGeSn ternaries are well suitable as drain since they offer a large indirect bandgap. The growth of such heterostructures with the desired band alignment is presented. The crystalline quality of the (Si)Ge(Sn) layers is similar to state-of-the-art SiGe layers.

Suppression of subcutaneous oxidation during the deposition of amorphous lanthanum aluminate on silicon

Amorphous LaAlO3 thin films have been deposited by molecular beam deposition directly on silicon without detectable oxidation of the underlying substrate. We have studied these abrupt interfaces by Auger electron spectroscopy, high-resolution transmission electron microscopy, medium-energy ion scattering, transmission infrared absorption spectroscopy, and x-ray photoelectron spectroscopy. Together these techniques indicate that the films are fully oxidized and have less than 0.2 A of SiO2 at the interface between the amorphous LaAlO3 and silicon. These heterostructures are being investigated for alternative gate dielectric applications and provide an opportunity to control the interface between the silicon and the gate dielectric.

Strain relaxation of epitaxial SiGe layers on Si(1 0 0) improved by hydrogen implantation

Abstract We propose a new method to fabricate strain relaxed high quality Si1−xGex layers on Si by hydrogen implantation and thermal annealing. Hydrogen implantation is used to form a narrow defect band slightly below the SiGe/Si interface. During subsequent annealing hydrogen platelets and cavities form, giving rise to strongly enhanced strain relaxation in the SiGe epilayer. As compared to thermally induced strain relaxed Si–Ge epilayers, the hydrogen implanted and annealed samples show a greatly reduced threading dislocation density and a much higher degree of strain relaxation (90%). We assume that the hydrogen induced defect band promotes strain relaxation via preferred nucleation of dislocation loops in the defect band which extend to the interface to form misfit segments. The samples have been investigated by X-ray diffraction, Rutherford backscattering spectrometry and transmission electron microscopy.

Effect of helium ion implantation and annealing on the relaxation behavior of pseudomorphic Si1−xGex buffer layers on Si (100) substrates

The influence of He implantation and annealing on the relaxation of Si0.7Ge0.3 layers on Si (100) substrates is investigated. Proper choice of the implantation energy results in a narrow defect band ≈100 nm underneath the substrate/epilayer interface. During annealing at 700–1000 °C, He-filled bubbles are created, which act as sources for misfit dislocations. Efficient annihilation of the threading dislocations is theoretically predicted, if a certain He bubble density with respect to the buffer layer thickness is maintained. The variation of the implantation dose and the annealing conditions changes density and size of spherical He bubbles, resulting in characteristic differences of the dislocation structure. Si1−xGex layers with Ge fractions up to 30 at. % relax the initial strain by 70% at an implantation dose of 2×1016 cm−2 and an annealing temperature as low as 850 °C. Simultaneously, a low threading dislocation density of 107 cm−2 is achieved. The strain relaxation mechanism in the presence of He fi...

Tensely strained GeSn alloys as optical gain media

This letter presents the epitaxial growth and characterization of a heterostructure for an electrically injected laser, based on a strained GeSn active well. The elastic strain within the GeSn well can be tuned from compressive to tensile by high quality large Sn content (Si)GeSn buffers. The optimum combination of tensile strain and Sn alloying softens the requirements upon indirect to direct bandgap transition. We theoretically discuss the strain-doping relation for maximum net gain in the GeSn active layer. Employing tensile strain of 0.5% enables reasonable high optical gain values for Ge0.94Sn0.06 and even without any n-type doping for Ge0.92Sn0.08.

Electrical characterization of amorphous lanthanum aluminate thin films grown by molecular-beam deposition on silicon

Amorphous LaAlO3 thin films were deposited at room temperature directly on n-type and p-type Si (001) by molecular beam deposition. The dielectric properties of the stoichiometric amorphous LaAlO3 thin films deposited on silicon were determined through capacitance-voltage and current-voltage measurements. The electrical measurements indicate that the amorphous LaAlO3 thin films have a dielectric constant (K) of K=16±2. This is significantly lower than the K=24 of crystalline LaAlO3. The equivalent oxide thickness values range between 9.8 and 15.5A for films deposited on n-type silicon with physical thicknesses of 45–75A.

Tensely strained silicon on SiGe produced by strain transfer

An approach for the controlled formation of thin strained silicon layers based on strain transfer in an epitaxial Si∕SiGe∕Si(100) heterostructure during the relaxation of the SiGe layer is established. He+ ion implantation and annealing is employed to initiate the relaxation process. The strain transfer between the two epilayers is explained as an inverse strain relaxation which we modeled in terms of the propagation of the dislocations through the layers. Effcient strain buildup in the Si top layer strongly depends on the Si top layer thickness and on the relaxation degree of the SiGe buffer. 100% strain transfer was observed up to a critical thickness of the strained silicon layer of 8nm for a 150nm relaxed Si0.74Ge0.26 buffer.

Si/SiGe electron resonant tunneling diodes

Resonant tunneling diodes have been fabricated using strained-Si wells and strained Si0.4Ge0.6 barriers on a relaxed Si0.8Ge0.2 n-type substrate, which demonstrate negative differential resistance ...

High performance Si/Si/sub 1-x/Ge x resonant tunneling diodes

Resonant tunneling diodes (RTDs) with strained i-Si/sub 0.4/Ge/sub 0.6/ potential barriers and a strained i-Si quantum well, all on a relaxed Si/sub 0.8/Ge/sub 0.2/ virtual substrate were successfully grown by ultra high vacuum compatible chemical vapor deposition and fabricated using standard Si processing methods. A large peak to valley current ratio of 2.9 and a peak current density of 4.3 kA/cm/sup 2/ at room temperature were recorded from pulsed and continuous dc current-voltage measurements, the highest reported values to date for Si/Si/sub 1-x/Ge/sub x/ RTDs. These dc figures of merit and material system render such structures suitable and highly compatible with present high speed and low power Si/Si/sub 1-x/Ge/sub x/ heterojunction field effect transistor based integrated circuits.