Using Quantum Confinement to Uniquely Identify Devices.

Modern technology unintentionally provides resources that enable the trust of everyday interactions to be undermined. Some authentication schemes address this issue using devices that give a unique output in response to a challenge. These signatures are generated by hard-to-predict physical responses derived from structural characteristics, which lend themselves to two different architectures, known as unique objects (UNOs) and physically unclonable functions (PUFs). The classical design of UNOs and PUFs limits their size and, in some cases, their security. Here we show that quantum confinement lends itself to the provision of unique identities at the nanoscale, by using fluctuations in tunnelling measurements through quantum wells in resonant tunnelling diodes (RTDs). This provides an uncomplicated measurement of identity without conventional resource limitations whilst providing robust security. The confined energy levels are highly sensitive to the specific nanostructure within each RTD, resulting in a distinct tunnelling spectrum for every device, as they contain a unique and unpredictable structure that is presently impossible to clone. This new class of authentication device operates with minimal resources in simple electronic structures above room temperature.

Elastic and vibrational properties of group IV semiconductors in empirical potential modelling.

We have developed an interatomic potential that with a single set of parameters is able to accurately describe at the same time the elastic, vibrational and thermodynamics properties of semiconductors. The simultaneous inclusion of radial and angular forces of the interacting atom pairs (short range) together with the influence of the broken crystal symmetry when the atomic arrangement is out of equilibrium (long range) results in correct predictions of all of the phonon dispersion spectrum and mode-Grüneisen parameters of silicon and germanium. The long range interactions are taken into account up to the second nearest neighbours, to correctly influence the elastic and vibrational properties, and therefore represent only a marginal computational cost compared to the full treatment of other proposed potentials.Results of molecular dynamics simulations are compared with those of ab initio calculations, showing that when our proposed potential is used to perform the initial stages of the structural relaxation, a significant reduction of the computational time needed during the geometry optimization of density functional theory simulations is observed.

An ab initio study of electronic and structural properties of Mn in a GaAs environment.

Based on ab initio calculations, we have investigated the atomic geometry, electronic properties and magnetic properties of Mn incorporation in GaAs. The inclusion of the Hubbard potential U in the calculation (namely with the σGGA+U scheme) results in the optimized geometry being contracted by approximately 2% relative to the relaxed geometry obtained by the (σGGA) method. Within both the σGGA and σGGA+U schemes the Mn impurity in bulk GaAs behaves like a d-hole with the majority spin state lying at 0.25 eV above the Fermi level. Theoretically simulated STM images for Mn/GaAs(110) indicate round protrusions at As sites and Ga sites, the latter being dependent on the Mn adsorption site (i.e. in different atomic layers). These results are supportive of a previous experimental STM image obtained with a very low Mn concentration.