The results of an accurate theoretical study on the effects of non-abrupt doping and interfacial profiles on the electron sheet density in one-side modulation-doped wurtzite GaN/AlGaN single quantum wells at low temperatures are presented. We solve coupled Schrödinger and Poisson equations self-consistently via the finite difference method. By employing a proper discretization on a nonuniform grid and taking into account the strong piezoelectric and spontaneous polarization fields exhibited by the wurtzite III-nitride heterostructures, a substantial increase in the 2DEG density is predicted with the increase of the donor diffusion length and the reduction of the spacer thickness.

We report a detailed analysis of how the existence of interface roughness can change exciton localization in CdTe/Cd1-xMn xTe strained double quantum wells (DQW´s) taking into account magnetic and electric field effects. We consider that the potential, effective mass, and the intrinsic magnetization are dependent on the profile of the Mn molar fraction at the interfacial region. Results obtained with CdTe/Cd0.68Mn0.32Te DQW´s show that the energy band tailoring generated by the strain and the Zeeman effect is responsible by a displacement of the exciton energy peaks and that small changes in the interface width (10 Å) can be responsible for 30 meV exciton energy broadening.

We investigate the confined exciton properties in InGaN/GaN cylindrical quantum wires. We have solved numerically Schrödinger-like equations in the effective mass approximation and have found the energy levels and wavefunctions for confined electrons and holes, using these results to calculate variationally the confined exciton energy. A comparison was made between graded and abrupt quantum wires, showing that the existence of smooth interfaces enhances the confined exciton energy if the wire radius is smaller than 50 Å. We conclude that the existence of graded interfaces must be considered for a better description of the exciton based optical properties of InGaN/GaN quantum wires.

We perform a theoretical investigation of the absorption and emission properties of quantum confined SiC/SiO2 spherical quantum dots, focusing on the the size-dependent emission and absorption spectra of an independent single dot. We observed strong oscillations in the absorption lines as a consequence of the interband transitions rules, and a blue-shift of the emission spectra lines with the decrease of the quantum dot diameter.

We report the development and characterization of high quality polyaniline-silicon heterojunction diodes appropriated for use as gas and/or ionizing radiation sensors. Polyaniline thin films 40 nm thick are an active part of the junction structure, that presents excellent electrical characteristics, with rectifying ratio of 50,000 at ± 1.0 Volt bias. The devices are very sensitive to gamma-radiation up to 6,000 Gy and to gas moistures such ammonia, nitric acid and trichloroethylene. The sensitivity of the diodes is observed through shifts of the current-voltage (I-V) curves which can be easily monitored to provide a calibration curve of the sensor either as a radiation dosimeter or as a gas sensor for use in applications in environments demanding gas monitoring or radiation dosimetry.

We performed comparative studies of radiation-induced interface trap generation at n-6H-SiC/SiO2 and Si/SiO2 interfaces for high doses of low energy x-rays in the range 0 to 200 Mrad (Si). We found that radiation-induced interface trap generation at the n-6H-SiC/SiO2 interface is much lower than at the Si/SiO2 interface. The experiments provide evidence of interface trap generation near the SiC conduction band associated with oxide traps.

The complex mobility of electrons in 3C - and 6H-SiC subjected to intense high frequency electric fields is calculated taking into account effects of band nonparabolicity. The electric field, given by a dc component plus an ac component in the frequency range 0.1-100 THz, is applied along the [0001] ([111]) direction in the hexagonal (cubic) polytype. The real electron mobility presents a characteristic maximum peaking around 6-8 THz, while the imaginary electron mobility is structured, with characteristic minimum and maximum around 2-3 THz and 20{30 THz, respectively. These mobilities are seen to smooth down for higher temperatures in both polytypes.

A study of the subpicosecond high-field electron transport transient in 3C- and 6H-SiC polytypes at high lattice temperatures is performed. Electric field intensities up to 1000 kV/cm and lattice temperatures of 300, 673, and 1073 K are considered. It is shown that the transient regime behavior depends on the electric field intensity as well as on the lattice temperature, but it is always shorter or of the order of 0.3 ps. For the lowest lattice temperature, an electron velocity overshoot can always occur when the electric field intensity is higher than 300 kV/cm, but it decreases and can even disappear when the lattice temperature is raised.