This work reports the growth of crystalline SrHf x Ti1−x O3 (SHTO) films on Ge (001) substrates by atomic layer deposition. Samples were prepared with different Hf content x to explore if strain, from tensile (x = 0) to compressive (x = 1), affected film crystallization temperature and how composition affected properties. Amorphous films grew at 225 °C and crystallized into epitaxial layers at annealing temperatures that varied monotonically with composition from ~530 °C (x = 0) to ~660 °C (x = 1). Transmission electron microscopy revealed abrupt interfaces. Electrical measurements revealed 0.1 A/cm2 leakage current at 1 MV/cm for x = 0.55.

The integration of dissimilar materials is highly desirable for many different types of device applications but often challenging to achieve in practice. The unrivalled imaging capabilities of the aberration-corrected electron microscope enable enhanced insights to be gained into the atomic arrangements across heterostructured interfaces. This paper provides an overview of our recent observations of oxide-semiconductor heterostructures using aberration-corrected high-angle annular-dark-field and large-angle bright-field imaging modes. The perovskite oxides studied include strontium titanate, barium titanate, and strontium hafnate, which were grown on Si(001) and/or Ge(001) substrates using the techniques of molecular-beam epitaxy or atomic-layer deposition. The oxide layers displayed excellent crystallinity and sharp, abrupt interfaces were observed with no sign of any amorphous interfacial layers. The Ge(001) substrate surfaces invariably showed both 1× and 2× periodicity consistent with preservation of the 2 × 1 surface reconstruction following oxide growth. Overall, the results augur well for the future development of functional oxide-based devices integrated on semiconductor substrates.

We report the epitaxial growth of γ-Al2O3 on SrTiO3 (STO) substrates by atomic layer deposition (ALD). The ALD growth of γ-Al2O3 on STO(001) single crystal substrates was performed at a temperature of 345 °C. Trimethylaluminum and water were used as co-reactants. In-situ reflection high-energy electron diffraction and ex-situ x-ray diffraction were used to determine the crystallinity of the Al2O3 films. In-situ x-ray photoelectron spectroscopy was used to characterize the Al2O3/STO heterointerface. The formation of a Ti3+ feature is observed in the Ti 2p spectrum of STO after the first few ALD cycles of Al2O3 and even after exposure of the STO substrate to trimethylaluminum alone at 345 °C. The presence of a Ti3+ feature is a direct indication of oxygen vacancies at the Al2O3/STO heterointerface, which provide the carriers for the quasi-two dimensional electron gas at the interface.

We present a theoretical study of the electronic structure, surface energies and work functions of orthorhombic Pt monosilicide and germanides of Pt, Ni, Y and Hf within the framework of density functional theory (DFT). Our calculated bulk structures are within 1-2% of reported experimental values. Calculated work functsions for the (001) surfaces of PtSi, NiGe and PtGe are 5.12, 4.57 and 4.83 eV, respectively, suggesting that these metals and their alloys can be used as self-aligned contacts to p-type silicon and germanium. Work functions for Y and Hf germanides range from 2.4 to 4.3 eV making them a possible n-type contact material. In addition, we also report an ab-initio calculation of the Schottky-barrier height at the Si(001)/PtSi(001) interface. The p-type Schottky barrier height of 0.28 eV is found in good agreement with predictions of a simple metal induced gap states (MIGS) theory and available experiment. This low barrier suggests PtSi as a low contact resistance junction metal for silicon CMOS technology. We identify the growth conditions necessary to stabilize this orientation.

Epitaxially grown oxide superlattices are attracting considerable attention due to their unusual properties and possible applications ranging from sensors to electronic devices [1]. We report a first-principles study of interfaces in the epitaxial LaAlO3/SrTiO3 system within density functional theory. We consider the electronic structure of the n-type interface, and compute the band alignment

In this paper we discuss a novel approach to the band gap engineering of semiconductors Si, Ge, GaAs and AIN. We suggest that nanoporous polymorphs of these materials may exist which would offer a significant variation of the electronic band gap. Structurally, nanoporous semiconductors are related to the zeolitic nets, and a systematic procedure of generating these structures from the (4;2) nets is described. We use the ab initio total energy quantum molecular dynamics method Fireball96 to investigate the energetics and the electronic properties of these nanoporous or “expanded” semiconductor phases.