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We have examined the origins of interlayer formation and misfit dislocation (MD) displacement in the vicinity of InAs/GaAs quantum dots (QDs). For QDs formed by the Stranski-Krastanov mode, regularly spaced MDs nucleate at the interface between the QD and the GaAs buffer layer. In the droplet epitaxy case, both In island formation and In-induced “nano-drilling” of the GaAs buffer layer are observed during In deposition. Upon annealing under As flux, the In islands are converted to InAs QDs, with an InGaAs interlayer at the QD/buffer interface. Meanwhile, MDs nucleate at the QD/interlayer interface.

Heterojunction interfaces between metal oxides are often highly lattice mismatched. The atomic and electronic structures of such interfaces, however, are not well understood. We have synthesized Cu 2O/TiO2 heterojunction thin films with 13% lattice mismatch and studied the interface via experimental methods and large-scale density function theory calculations of supercells containing ∼1300 atoms. We find that an interface of epitaxial quality is formed via a coincidence site lattice of 8 Cu 2O unit cells matching 9 TiO2 unit cells. Calculations reveal the existence of a dislocation core of the O sublattices at the interface and a random arrangement of one layer of interfacial Cu atoms. The interfacial electronic structure is found to be mostly determined by the interfacial Cu distribution, rather than by the O dislocation core. The conduction band minimum and valence band maximum states are spatially separated, and there is no strongly localized state near the core.

We have examined the formation mechanisms of InAs quantum dots (QDs) via annealing In islands under As flux. We report two distinct mechanisms, droplet epitaxy (DE) and solid phase epitaxy (SPE), which depend on As surface coverage. On c(4 × 4) GaAs surfaces, QDs form by DE. For c(4 × 4)α, one-to-one conversion from In islands to InAs QDs is observed. For c(4 × 4)β, lower densities of larger QDs are observed, presumably due to enhanced In surface diffusion in the absence of metastable Ga-As dimers. For the As capped surface, In deposition leads to an amorphous film, from which QDs nucleate by SPE during annealing.

Asif Islam Khan, Debanjan Bhowmik, Pu Yu, Sung Joo Kim, Xiaoqing Pan et al. Citation: Appl. Phys. Lett. 100, 089904 (2012); doi: 10.1063/1.3675884 View online: http://dx.doi.org/10.1063/1.3675884 View Table of Contents: http://apl.aip.org/resource/1/APPLAB/v100/i8 Published by the AIP Publishing LLC.

We report a proof-of-concept demonstration of negative capacitance effect in a nanoscale ferroelectric-dielectric heterostructure. In a bilayer of ferroelectric, Pb(Zr0.2Ti0.8)O3 and dielectric, SrTiO3, the composite capacitance was observed to be larger than the constituent SrTiO3 capacitance, indicating an effective negative capacitance of the constituent Pb(Zr0.2Ti0.8)O3 layer. Temperature is shown to be an effective tuning parameter for the ferroelectric negative capacitance and the degree of capacitance enhancement in the heterostructure. Landau's mean field theory based calculations show qualitative agreement with observed effects. This work underpins the possibility that by replacing gate oxides by ferroelectrics in MOSFETs, the sub threshold slope can be lowered below the classical limit (60 mV/decade).