Anodization of Ti by high electric fields at the tip of a scanned probe can be used to produce nanoscale features consisting of oxides of Ti. In this manner, Ti can be used as a sacrificial resist for nanoscale lithography by exploiting the etching selectivity differences between Ti and anodized Ti. The anodization was accomplished with an atomic force microscope using Ticoated silicon nitride cantilevers. The anodizing bias voltage is applied to the tip and is independent of the feedback, unlike the scanning tunneling microscope. With this setup we were able to fabricate sub-40 nm lines by direct anodization of Ti. It is also shown that once tip and sample are brought into hard contact, subsequent bending of the cantilever has little effect on the linewidth or thickness of the anodized material.

Full electric-field control of spin orientations is one of the key tasks in semiconductor spintronics. We demonstrate that electric-field pulses can be utilized for phase-coherent ±π spin rotation of optically generated electron spin packets in InGaAs epilayers detected by time-resolved Faraday rotation. Through spin-orbit interaction, the electric-field pulses act as local magnetic field pulses. By the temporal control of the local magnetic field pulses, we can turn on and off electron spin precession and thereby rotate the spin direction into arbitrary orientations in a two-dimensional plane. Furthermore, we demonstrate a spin-echo-type spin drift experiment and find an unexpected partial spin rephasing, which is evident by a doubling of the spin dephasing time.

Blue-green (λ=511 nm) separate confinement laser structures based on lattice-matched MgZnSSe-ZnSSe-CdZnSe have been grown by molecular beam epitaxy. Wide stripe gain-guided devices have been fabricated from several such wafers. These devices exhibit room-temperature pulsed threshold current densities as low as 630 A/cm2 and threshold voltages less than 9 V. Using a novel self-aligned process that results in a planar surface, buried-ridge laser diodes have also been fabricated. These devices have demonstrated room-temperature threshold currents as low as 2.5 mA, which is more than a factor of 50 lower than that of any previously reported II-VI laser diode. Room-temperature operation at duty factors up to 50% has been demonstrated. The far-field patterns from these devices indicate single lateral mode operation, suitable for diffraction-limited applications, such as optical data storage.

In this work, the effect of spin-orbit coupling in two-dimensional electron gases and quantum wire structures is discussed. First, the theoretical framework is introduced including spin-orbit coupling due to structural inversion asymmetry, the so-called Rashba effect, as well as the Dresselhaus term. The latter originates from bulk inversion asymmetry. With regard to wire structures, special attention is devoted to the influence of the particular shape of the confinement potential on the energy spectrum. As a model system Ga x In 1−x As/InP heterostructures are chosen, where different thicknesses of the strained Ga 0.23 In 0.77 As channel layer were introduced, in order to adjust the strength of the spin-orbit coupling. Hall bar structures as well as sets of identical wires with different widths were prepared. In two-dimensional electron gases, the strength of the spin-orbit coupling was extracted by analyzing the characteristic beating pattern in the Shubnikov-de Haas oscillations. In addition, the weak antilocalization was utilized to obtain information on the spin-orbit coupling. It is shown that for decreasing width of the strained layer the Rashba effect, which dominates in our layer systems, is increased. This behavior is attributed to the larger interface contribution if the electron wavefunction is strongly confined. The measurements on the wire structures revealed a transition from weak antilocalization to weak localization if the wire width is decreased. This effect is attributed to an enhanced spin diffusion length for strongly confined systems.