We describe the clinical history of a 49-year old woman, who demonstrated progressive personality changes more than twenty years after radiation of a pituitary adenoma (prolactinoma), with apathy, loss of initiative, memory deficits, postural instability, dysarthria and faecal incontinence. Neuropsychological assessment showed impulsivity, loss of overview, desinhibition, fluctuating deficits of attention, and memory disturbances. MRI-scanning of the brain revealed a cystic lesion along the right ventricle. The clinical picture and the findings of the other investigations are typical for dementia due to radiation encephalopathy. Such a long period between radiation and cognitive deterioration is rare, although it has been described before.

Background. Past research has demonstrated that depression is associated with dysfunctional processing of emotional information. Recent studies demonstrate that a bias in the attentional processing of negative information may be an important cognitive vulnerability factor underlying the onset and maintenance of depression. However, to date, the nature of this attentional bias is still poorly understood and further exploration of this topic to advance current knowledge of attentional biases in depression seems imperative.

Method. This study examined attentional biases for angry facial expressions presented for 1000 ms in 20 patients with major depressive disorder (MDD) and 20 non-depressed control participants (NC) matched for age and gender using an emotional modification of the Exogenous Cueing task.

Results. Patients with MDD showed maintained attention for angry faces compared with neutral faces. In comparison with non-depressed participants they showed a stronger attentional engagement for angry faces. In contrast, the NC group directed attention away from angry faces, more rapidly disengaging their attention compared with neutral faces.

Conclusions. This pattern of results supports the assumption that MDD is characterized by deficits in the attentional processing of negative, interpersonal information and suggests a ‘protective’ bias in non-depressed individuals. Implications in relation to previous research exploring cognitive and interpersonal functioning in depression are discussed.

Ohmic contacts are optimized on δ-doped lattice-matched (x=0.53) and pseudomorphic (x=0.80) lno.53Gao.47As/Alo.52Ino.48As/InxGa1-xAs/AI0.52ln0.48As layers grown on InP by molecular beam epitaxy (MBE). The layers are characterized by temperature-dependent Hall measurements (4-300 K) and Shubnikov-de Haas measurements at 1.2 K. Lowest specific transfer resistance (< 0.1 O.mm) is obtained with a Ni/AuGe/Ni/Au metal sequence alloyed at 280 °C for 1 min. The influence of the Ni content in the metallization is studied and AuGe layers evaporated from the eutectic composition (Au:Ge, 88:12 weight %) are compared with successively evaporated Au and Ge layers. It is shown that the resulting contact resistance is not very sensitive to changes in these parameters. The solid state reactions involved are studied by sputter Auger depth profiling.

The damage introduced by CH4/H2 reactive ion etching (RIE) on Si-doped AlGaAs layers is studied by X-Ray Photoelectron Spectroscopy (XPS), Auger electron spectrocopy (AES) and electrical measurements on Schottky contacts. The XPS analysis of the surface stoichiometry after RIE exposure shows arsenic depletion and adsorbed carbon as the main characteristics. The carbon spectrum consists of a component due to atmospheric contamination and an additional photoelectron peak at 283 eV, which we correlate with the formation of Ga-C radicals at the AlGaAs surface during RIE. The reaction process at the Au/TiW/Ti/AlGaAs interface after RIE exposure and subsequent thermal annealing is monitored by AES. Also by this technique, carbon was detected at the Ti/AlGaAs interface and no interdiffusion was observed. The electrical behaviour of the contacts is characterized by capacitance-voltage (CV) and current-voltage (IV) measurements. Schottky barrier height, ideality factor and reverse breakdown were determined. The barrier height extracted from CV measurements of the samples exposed to RIE shows increased values (1.1 to 1.4 eV) compared to the reference samples (1.0 to 1.1 eV), depending on the aluminium concentration. The same behaviour was observed in the ideality factor. The results are explained by the formation of a p-n junction below the metal/AlGaAs barrier. Good agreement between experimental and theoretical values is found when the compensation of Si donors was taken into account.

The damage introduced by CH4/H2 reactive ion etching (RIE) and its recovery after thermal annealing has been investigated by Hall measurements and low temperature photoluminescence (PL) on pseudomorphic AlGaAs/InGaAs modulation doped structures. After plasma exposure, the PL intensity has significantly decreased and shifted in energy. In order to study the recovery of the damage introduced by the plasma, thermal annealing was done at temperatures between 350 and 500°C. We observed that the luminescence emission is totally recovered after annealing at 450°C. Hall measurements at room temperature (RT) and at 77K showed that the electrical characteristics of these structures can be restored only after thermal annealing at 500°C.

The optimised etching conditions have been applied in a fabrication process for submicron dry gate recessed pseudomorphic delta-doped AlGaAs/InGaAs modulation doped field effect transistors (MODFETs). For a 0.25 mm gatelength device the maximum DC transconductance value was as high as 680 mS/mm. The same value was extracted from measurements at 15 GHz.

InAs and InAs0.85Sb0.15p-“i”-n structures were grown on InAs, GaAs and Si substrates by Molecular Beam Epitaxy. The structural quality of the layers is discussed using Transmission Electron Microscopy and Rutherford Back Scattering. The influence of the material quality on the 77 K current-voltage measurements is explained. The spectral response of the devices was measured demonstrating peak responsivities of 2.1 A/W at 3.5μm wavelength for InAs0.85Sb0.15 detectors with a 4.3 μm cut-off wavelength.

We report for the first time the realization of submicron pseudomorphic Al.15, Ga.85As-In.20Ga.80As HEMT’s with non-alloyed Pd/Ge ohmic coi tacts. Best results of contact resistance were obtained at a sintering temperature of 340°C with values as low as 0.057 Ωmm. Enhanced contrast, needed for accurate alignment of the gate by electron-beam lithography, was obtained by using Pd/Ge/Ti/Pd and Pd/Ge/Ti/Pt metal sequences. These contacts exhibited even lower contact resistances than the standard Pd/Ge contacts. Although Pd/Ge/Ti/Pd exhibits good morphology, reaction is witnessed at the edges, reducing the accuracy of alignment.

Processed enhancement mode devices exhibit maximum transconductances in excess of 520 mS/mm and currents of 300 mA/mm for 0.3 micron gatelength. This study shows that the contact resistance is no longer a restriction for obtaining very high transconductances in high performance devices.

The behavior of Si and Be impurities in InAsx Sb1−x (0.05<x<0.45) heteroepitaxial layers grown on GaAs-coated Si by MBE is characterised. Siis found to act as an n-type dopant for the growth conditions used. The calibration of the Si n-type doping as a function of the Sisource temperature is obtained by infrared absorption spectrometry, stripping Hall and SIMS depth profiling. At high doping levels the amphoterical characterof the Si impurities becomes evident. SIMS is used to investigate the dopant incorporation and the formation of diode structures. The influence of the mismatched epitaxy on the transport properties is investigated by stripping Hall measurements. In order to establish the correlation between crystalline properties of the epilayers and the ability to fabricate diodes, we compare the defect structure of InAs and In(As)Sb p-'i'-n diodes.

The paper presents a systematic study of grown-in and process-induced defects on LEC GaAs substrates. Defects have been revealed by photoetching the wafers with diluted Sirti-like solutions after various processing steps. MESFET arrays have been processed on the wafers and a systematic mapping of the I-V characteristics has been performed. A correlation between various defect configurations and the FET threshold voltage shifts has been established.