Salvatore Cina

Tunable, Strongly Non parabolic Confinement in a Quasi-One-Dimensional Electron Gas Formed by Epitaxial Regrowth.

A new type of quasi-one-dimensional electron gas (Q1DEG) characterised by a tunable, strongly non parabolic confining potential in the lateral direction has been produced, using molecular beam epitaxy to grow a high-mobility heterostructure on a (311)A GaAs substrate selectively etched to expose (100) facets. The electron gas on the (100) facets is confined in one dimension by the two-dimensional hole gases on the (311)A facets, forming a p-n-p structure. Infrared cyclotron resonance (CR), magneto resistance and electron-beam-induced current (EBIC) measurements have been made on these Q1DEGs for various biases (Vh) between the hole and electron gases to investigate its effects on the confinement potential. Two different regimes are present. For Vh>-1.9 V, a strong peak attributable to a confined magnetoplasmon (CPM), together with its higher-frequency harmonics, are observed in the CR spectra. For Vh<-1.9 V, a new mode appears and the CPM no longer fits the experimental data. The anomalous dependence of the resonance frequency on carrier density, together with the EBIC images, provides some understanding of the tunable, non parabolic nature of the confining potential.

Very-high-brightness diodes for passive-matrix display applications

The development of a high-brightness low-voltage yellow-light-emitting polymer system suitable for use in low-cost passive-matrix displays will be reported. Average device efficiencies of 16 Im/W at 100 and 1000 cd/m 2 are achieved at 2.1 and 2.4 V, respectively. A luminance level of 100,000 cd/m 2 is achieved at 5.5 V.

Lifetime of blue polymer LEDs

Summary form only given. We have shown lifetimes in excess of 5000 hours for a blue material, which is considered sufficient for some first generation applications. This improvement in lifetime has been partly due to the introduction of new polymer materials with higher glass transition temperatures and partly to the optimisation of device fabrication procedures including the use of a baking step in the process, which leads to further lifetime enhancements.

Novel effects produced on a two dimensional electron gas by introducing InAs dots in the plane of the quantum well

Abstract We show that the presence of InAs dots embedded in a host GaAs quantum well containing a two-dimensional electron gas dramatically modifies the cyclotron resonance (CR). Far-infrared CR measurements show two modes with different dispersions with applied magnetic field B . The lower-frequency mode, with a sub-linear dependence on B , is identified as a CR at low B , developing into a skipping orbit around the dot perimeters at higher B . This has not been previously observed for a system with randomly distributed scatterers. The higher-frequency mode is identified as a magnetoplasmon localised by the confining effect of the arrays of repulsive potentials due to the dots in the well.

Far-infrared spectroscopy of a two-dimensional electron gas in a tunable, periodically modulated magnetic field

Abstract We report on the first infrared optical measurements of a two-dimensional electron gas (2DEG) in the presence of an external periodically modulated perpendicular magnetic field, realised using epitaxial regrowth to produce a corrugated quantum well (QW). Two active modes are observed, with relative intensities and resonance frequencies depending on the amplitude of the magnetic field modulation as well as on the total external magnetic field. The two modes are interpreted as being magnetoplasmons coupled by the presence of the magnetic field modulation. The magnetoplasmons band structure calculation has been used to describe the experimental data. The agreement between theory and experiment is excellent.

Far-infarared study of a quasi-one-dimensional electron gas formed on (100) GaAs with hole gas sidegates on a (311)A GaAs substrate

Abstract A new type of quasi-one-dimensional electron gas (Q1DEG) has been produced using molecular beam epitaxy to grow a high mobility heterostructure on a (311)A GaAs substrate selectively etched to expose (100) facets. The electron gas on the (100) facets is confined in one dimension by the two-dimensional hole gases on the (311)A faces, forming a p–n–p structure. Fourier transform infrared (FTIR) cyclotron resonance (CR) measurements and magneto–resistance measurements have been made on these Q1DEGs for various biases ( V h ) between the hole and electron gases to investigate its effects on the confinement potential, the Q1DEG effective width and the areal carrier density N s . In the presence of a magnetic field the FTIR spectra show a strong peak attributable to a confined magnetoplasmon excited parallel to the lateral confinement direction. Weaker peaks occur at higher frequencies corresponding to harmonics. For all the peaks the magnetoplasma frequency falls with decreasing V h until a threshold is reached at which the trend changes dramatically and a new mode appears. This behaviour is discussed in terms of nonparabolicity of the confining potential.