In this work, a nonlinear variational linear combination of atomic orbitals scheme we introduced recently (Lima et al 2007 Phys. Rev. B 75 073201) for studying hydrogenic systems in semiconductors is adapted for the computation of the effect of a high-frequency, intense laser field on the positronium (Ps) quantum states. Our nonperturbative approach, based upon the Kramers-Henneberger translation transformation, allows us to show that, for sufficiently high intensities, the radiation field induces a wavefunction dichotomy, which causes a reduction on the positronium decay probability (i.e., enhances its lifetime). Our results point out that an enhancement of up to four orders of magnitude in the Ps lifetime can be attained with the current laser technology. Our careful quantitative analysis also corrects some mistakes in the approximate formulae proposed by Ehlotzky in a previous work (Ehlotzky 1988 Phys. Lett. A 126 524).

We report on the fabrication of silicon carbide/polyaniline heterojunctions produced by spin coating of polyaniline films onto n-type 6H-SiC and 4H-SiC substrates. Atomic force microscopy was used to estimate the surface roughness, and their electrical characteristics were investigated by means of current, capacitance and conductance measurements as a function of frequency and voltages. Reproducible characteristics and rectification ratios as high as 2 × 106 at ±2 V for the 6H-SiC based heterojunctions were obtained. The devices were modelled as Schottky diodes with series resistance and an oxide interfacial oxide layer to account for interface traps. By analysing the forward bias I–V characteristics, we found that the interface trap density for 4H-SiC/PANI heterojunctions is approximately one order of magnitude higher than for 6H-SiC/PANI heterojunctions, which is consistent with previous studies on SiC/SiO2 interface traps. The average value of interface trap densities for 6H-SiC devices was 8.4 × 1011 eV−1 cm−2 and for 4H-SiC it was 2.7 × 1013 eV−1 cm−2. These values are in the range of previous reports on Schottky diodes with polymer layers.

There are many studies on the synthesis and structure of mesoporous silica, but few reports on mesoporous silica-based electronic devices using planar technology. Fabrication of low-k insulator films from mesoporous silica has been investigated for years. Trapped water is a nuisance for those intending to use mesoporous silica films as low-k materials, but may be beneficial for other applications. In this work, we fabricated Si metal-insulator-semiconductor capacitors (MIS) with a hexagonal mesoporous silica (MCM-41) film as the dielectric and studied their electrical characteristics. We show that water confined within the dielectric is associated with high values of capacitance per unit area (approximately 1 μF cm −2 at 100 Hz) and frequency dispersion of the accumulation capacitance. These devices hold potential for the development of high value MIS capacitors, sensors and biosensors.

We compared SiO2/SiC interface characteristics for three different oxidation processes (dry-oxygen, water-containing oxygen and water-containing nitrogen atmospheres). Metal-oxide-semiconductor (MOS) structures were fabricated on 8° off-axis 4H-SiC(0001) n- and p-type epitaxial wafers. Electrical characteristics were obtained by I–V measurements, high-frequency capacitance–voltage (C–V) and ac conductance (G–V and G–ω) methods. The samples were also characterized by x-ray photoelectron spectroscopy. Results evidence a remarkable difference between n- and p-type doped samples. The p-type samples showed effective oxide charge density up to three orders of magnitude higher than n-type. This fact was explained by the capturing of majority carriers in near interface oxide traps.

The electrical and optical properties of heterojunctions formed by thermally deposited ZnO thin films on n-type 4H-SiC substrates have been investigated. Current-voltage characteristics of the fabricated light emitting devices revealed excellent rectifying behaviors with a typical leakage current lower than 1 nA at a reverse bias of −3 V, and with a forward current at 3 V in the range of 2 mA. A study of the electroluminescent characteristics of ZnO/SiC heterojunctions over the temperature range of 50-450 K showed an emission peak around 410 nm and a broad defect-related electroluminescence at room temperature in the visible range for a forward current of 300 mA. Electrically active deep level centers in ZnO and n-type 4H-SiC epilayers have been investigated by deep level transient spectroscopy (DLTS) and high-resolution Laplace DLTS (LDLTS). Additionally, LDLTS has successfully been employed to resolve the closely spaced hole trap energy levels.