The results of magnetoconductivity measurements in GaInAs quantum wells are presented. The observed magnetoconductivity appears due to the quantum interference, which lead to the weak localization effect. It is established that the details of the weak localization are controlled by the spin splitting of electron spectra. A theory is developed which takes into account both linear and cubic in electron wave vector terms in spin splitting, which arise due to the lack of inversion center in the crystal, as well as the linear terms which appear when the well itself is asymmetric. It is established that, unlike spin relaxation rate, contributions of different terms into magnetoconductivity are not additive. It is demonstrated that in the interval of electron densities under investigation ((0.98 − 1.85)·1012 cm −2 ) all three contribution are comparable and have to be taken into account to achieve a good agreement between the theory and experiment. The results obtained from comparison of the experiment and the theory have allowed us to determine what mechanisms dominate the spin relaxation in quantum wells and to improve the accuracy of determination of spin splitting parameters in A3B5 crystals and 2D structures. 73.20.Fz,73.70.Jt,71.20.Ej,72.20.My

A dramatic increase of the conduction band electron mass in a nitrogen-containing III–V alloy is reported. The mass is found to be strongly dependent on the nitrogen content and the electron concentration with a value as large as 0.4m0 in In0.08Ga0.92As0.967N0.033 with 6×1019 cm−3 free electrons. This mass is more than five times larger than the electron effective mass in GaAs and comparable to typical heavy hole masses in III–V compounds. The results provide a critical test and fully confirm the predictions of the recently proposed band anticrossing model of the electronic structure of the III–N–V alloys.

We report on room temperature terahertz generation by a submicron size AlGaN/GaN-based high electron mobility transistors. The emission peak is found to be tunable by the gate voltage between 0.75 and 2.1 THz. Radiation frequencies correspond to the lowest fundamental plasma mode in the gated region of the transistor channel. Emission appears at a certain drain bias in a thresholdlike manner. Observed emission is interpreted as a result of Dyakonov-Shur plasma wave instability in the gated two-dimensional electron gas.

Double-barrier GaN resonant tunneling diodes with AlGaN barriers were fabricated on bulk (0001) single-crystal GaN substrates. Layers were grown using molecular-beam epitaxy with a rf plasma nitrogen source. Single diodes of 6μm diameter were prepared by inductively coupled plasma reactive ion etching. For many diodes clear negative differential resistance is observed around 2V with peak currents around 10kA∕cm2 and a peak-to-valley ratio of about 2 at room temperature. Its observation does not depend on specific conditions of measurement; however, it slowly decays after each measurement. The mechanism behind this decay is investigated since it is obviously prohibiting the usage of GaN resonant tunneling diodes so far. It is shown not to be caused by catastrophic breakdown of the devices.

Dislocation-free high-quality AlGaN/GaN heterostructures have been grown by molecular-beam epitaxy on semi-insulating bulk GaN substrates. Hall measurements performed in the 300 K–50 mK range show a low-temperature electron mobility exceeding 60 000 cm2/V s for an electron sheet density of 2.4×1012 cm−2. Magnetotransport experiments performed up to 15 T exhibit well-defined quantum Hall-effect features. The structures corresponding to the cyclotron and spin splitting were clearly resolved. From an analysis of the Shubnikov de Hass oscillations and the low-temperature mobility we found the quantum and transport scattering times to be 0.4 and 8.2 ps, respectively. The high ratio of the scattering to quantum relaxation time indicates that the main scattering mechanisms, at low temperatures, are due to long-range potentials, such as Coulomb potentials of ionized impurities.

In this paper, we carry out a comprehensive review of the nitrogen-induced modifications of the electronic structure of Ga 1−y In y N x As 1−x alloys. We study in detail the behaviour of the conduction-band effective mass as a function of Fermi energy, nitrogen content and pressure. From measurements of the plasma frequency for samples with different electron concentrations we have determined the dispersion relation for the lowest conduction band. We have also studied composition, temperature and pressure dependent optical absorption spectra on free-standing layers of Ga 1−y In y N x As 1−x (0 x 0.025 and 0 y 0.09) lattice-matched to GaAs. Spectroscopic ellipsometry measurements performed in a wide photon energy range from 1.5 to 5.5 eV have been used to determine the energy dependence of the dielectric function as well as the energies of E 1 , E 0 and E 2 critical point transitions. Experiments have shown that nitrogen has a large effect on the dispersion relations and on the optical spectra for the conduction-band states close to the point. A much smaller effect has been observed for X and L minima as well as for the valence-band states. We have compared our results with other available experimental data. The results are analysed in terms of the analytical band anti-crossing model as well as the local density approximation calculations and empirical pseudopotential models.

The results on growth and magnetotransport characterization of AlGaN∕GaN heterostructures obtained by plasma assisted molecular beam epitaxy on dislocation-free (below 100cm−2) GaN high pressure synthesized bulk substrates are presented. The record mobilities of the two dimensional electron gas (2DEG) exceeding 100000cm2∕Vs at liquid helium temperature and 2500cm2∕Vs at room temperature are reported. An analysis of the high field conductivity tensor components allowed us to discuss the main electron scattering mechanisms and to confirm unambiguously the 2DEG room temperature mobility values.

Using reflectance spectroscopy, the in-plane polarization behavior of unstrained C- and A-plane GaN films is experimentally investigated. While no in-plane polarization anisotropy is observed for all three band-gap related excitons (A, B, and C) in unstrained C-plane GaN films, the A exciton is completely linearly polarized perpendicular to the c axis in unstrained A-plane GaN films. However, the B and C excitons are only partially polarized. This observation is in excellent agreement with results based on band-structure calculations using the Bir-Pikus Hamiltonian for the wurtzite crystal structure.