Chemical tuning of metal-semiconductor interfaces

First principles optical spectra of the β-SiC(0 0 1)/Al interface

The optical spectra of the β-SiC(0 0 1)/Al interface has been studied using first principles time-dependent density functional theory. We considered the bare random phase approximation as well as two different exchange-correlation kernels, i.e. the adiabatic-local-density-approximation and the jellium-with-gap kernel of Trevisanutto et al (2013 Phys. Rev. B 87 205143). We investigated the C-terminated interface with Al-C interaction which has quite good bond adhesion between the two materials. The absorption spectra of all methods are dependent on the electric field polarization, showing high anisotropy in these systems. When the electric field is parallel to the interface plane, all methods predict a metallic behavior, while enhanced semiconductor excitonic effects are present when the electric field is perpendicular to the interface plane. Between the considered methods, the jellium-with-gap kernel enhances the excitonic effects of the β-SiC(0 0 1)/Al interface with respect to the other methods.

Tuning of the Rashba effect in Pb quantum well states via a variable Schottky barrier

Spin-orbit interaction (SOI) in low-dimensional systems results in the fascinating property of spin-momentum locking. In a Rashba system the inversion symmetry normal to the plane of a two-dimensional (2D) electron gas is broken, generating a Fermi surface spin texture reminiscent of spin vortices of different radii which can be exploited in spin-based devices. Crucial for any application is the possibility to tune the momentum splitting through an external parameter. Here we show that in Pb quantum well states (QWS) the Rashba splitting depends on the Si substrate doping. Our results imply a doping dependence of the Schottky barrier which shifts the Si valence band relative to the QWS. A similar shift can be achieved by an external gate voltage or ultra-short laser pulses, opening up the possibility of terahertz spintronics.

Interface effects on the quantum well states of Pb thin films

Using scanning tunneling spectroscopy, we have studied the interface effect on quantum well states of Pb thin films grown on various metal-terminated (Pb, Ag, and Au) n-type Si(111) surfaces and on two different p-type Si(111) surfaces. The dispersion relation E(k) of the electrons of the Pb film and the phase shift at the substrate interface were determined by applying the quantization rule to the measured energy positions of the quantum well states. Characteristic features in the phase shift versus energy curves were identified and were correlated to the directional conduction band of the silicon substrate and to the Schottky barrier formed between the metal film and the semiconductor. A model involving the band structure of the substrate, the Schottky barrier, and the effective thickness of the interface was introduced to qualitatively but comprehensively explain all the observed features of the phase shift at the substrate interface. Our physical understanding of the phase shift is critically important for using interface modification to control the quantum well states.

Spin and angle resolved photoemission on non-magnetic low-dimensional systems

The electronic structure of non-magnetic low-dimensional materials can acquire a spin structure due to the breaking of the inversion symmetry at the surface or interface. This so-called Rashba effect is a prime candidate for the manipulation of the electron spin without using any magnetic fields. This is crucial for the emerging field of spintronics, where the spin of the electron instead of its charge is used to transport or store information. Spin and angle resolved photoemission is currently one of the main experimental methods to measure the spin resolved electronic structure, which contains all the relevant information for spintronics. In this review, the technique of spin and angle resolved photoemission will be explained and recent results on low-dimensional non-magnetic structures will be discussed.

Controlling the thermal stability of thin films by interfacial engineering

The quantized electronic structure in Pb films on Si(111) varies substantially as the film thickness increases. The changes in electronic energy cause the thermal stability of the films to oscillate with an approximate bilayer period. The phase of the oscillations can be controlled by interfacial engineering. Comparison of Pb films prepared on Si(111) terminated by In, Au, and Pb as interfactants reveals a phase reversal. For , films made of odd numbers of atomic layers (5, 7, and 9) are more stable than the even ones. This trend is reversed for the other two cases.

Switching between one and two dimensions: conductivity of Pb-induced chain structures on Si(557)

We show in a combined study of four-point conductance measurement and tunneling microscopy that surface state conductance induced by one monolayer of Pb on Si(557) can be quasi one dimensional with conductivity values close to typical three-dimensional metals. At a critical temperature of Tc = 78 K, associated with an order-disorder phase transition and a tenfold superperiodicity along the Pb chains, the system switches from low to high conductance anisotropy, with a semiconductor-insulator transition in the direction perpendicular to the chain structure, while along the chains conductance with a (1/T + const) temperature dependence was found.