Aims. In March 2008, the APEX facility instrument was installed on the telescope at the site of Lliano Chajnantor in northern Chile. The main objective of the paper is to introduce the new instrument to the radio astronomical community. It describes the hardware configuration and presents some initial results from the on-sky commissioning. Methods. The heterodyne instrument covers frequencies between 211 GHz and 1390 GHz divided into four bands. The first three bands are sideband-separating mixers operating in a single sideband mode and based on superconductor-insulator-superconductor (SIS) tunnel junctions. The fourth band is a hot-electron bolometer, waveguide balanced mixer. All bands are integrated in a closedcycle temperature-stabilized cryostat and are cooled to 4 K. Results. We present results from noise temperature, sideband separation ratios, beam, and stability measurements performed on the telescope as a part of the receiver technical commissioning. Examples of broad extragalactic lines are also included.

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This paper demonstrates how sodium enhanced oxidation of Si face 4H-SiC results in removal of near-interface traps at the SiO2∕4H-SiC interface. These detrimental traps have energy levels close to the SiC conduction band edge and are responsible for low electron inversion channel mobilities (1–10cm2∕Vs) in Si face 4H-SiC metal-oxide-semiconductor field effect transistors. The presence of sodium during oxidation increases the oxidation rate and suppresses formation of these near-interface traps resulting in high inversion channel mobility of 150cm2∕Vs in such transistors. Sodium is incorporated by using carrier boats made of sintered alumina during oxidation or by deliberate sodium contamination of the oxide during the formation of the SiC∕SiO2 interface.

We report on electrical properties and microstructure of epitaxial thin NbN films grown on 3C-SiC/Si substrates by means of reactive magnetron sputtering. A complete epitaxial growth at the NbN/3C-SiC interface has been confirmed by means of high-resolution transmission electron microscopy (HRTEM) along with x-ray diffractometry (XRD). Resistivity measurements of the films have shown that the superconducting transition onset temperature (T C) for the best specimen is 11.8 K. Using these epitaxial NbN films, we have fabricated submicron-size hot-electron bolometer (HEB) devices on 3C-SiC/Si substrate and performed their complete DC characterization. The observed critical temperature T C = 11.3 K and critical current density of about 2.5 MA/cm 2 at 4.2 K of the submicron-size bridges were uniform across the sample. This suggests that the deposited NbN films possess the necessary homogeneity to sustain reliable hot electron bolometer device fabrication for THz mixer applications.

In this paper, we present studies of room temperature aging and annealing of Nb/ Al-AlO x / Nb tunnel junctions with the size of 2 -3 m 2 . We observed a noticeable drop of junction normal resistance R n unusually combined with increase in subgap resistance R j as a result of aging. Variation in both R n and R j are subject to the junction size effect. An effect of aging history on the junction degradation after consequent annealing was discovered. Discussion and interpretation of the observed phenomena are presented in terms of structural ordering and reconstruction in the AlO x layer, driven by diffusion flows enhanced due to stress relaxation processes in the Al layer interfacing the AlO x layer.