Electron spin relaxation in cubic GaN quantum dots

The spin relaxation time $T_{1}$ in zinc blende GaN quantum dot is investigated for different magnetic field, well width and quantum dot diameter. The spin relaxation caused by the two most important spin relaxation mechanisms in zinc blende semiconductor quantum dots, {i.e.} the electron-phonon scattering in conjunction with the Dresselhaus spin-orbit coupling and the second-order process of the hyperfine interaction combined with the electron-phonon scattering, are systematically studied. The relative importance of the two mechanisms are compared in detail under different conditions. It is found that due to the small spin orbit coupling in GaN, the spin relaxation caused by the second-order process of the hyperfine interaction combined with the electron-phonon scattering plays much more important role than it does in the quantum dot with narrower band gap and larger spin-orbit coupling, such as GaAs and InAs.Comment: 8 pages, 5 figures, PRB 79, 2009, in pres

Spin orbit coupling in bulk ZnO and GaN

Using group theory and Kane-like $\mathbf{k\cdot p}$ model together with the L\"owdining partition method, we derive the expressions of spin-orbit coupling of electrons and holes, including the linear-$k$ Rashba term due to the intrinsic structure inversion asymmetry and the cubic-$k$ Dresselhaus term due to the bulk inversion asymmetry in wurtzite semiconductors. The coefficients of the electron and hole Dresselhaus terms of ZnO and GaN in wurtzite structure and GaN in zinc-blende structure are calculated using the nearest-neighbor $sp^3$ and $sp^3s^\ast$ tight-binding models separately.Comment: 9 pages, 6 figures, to be published in J. Appl. Phy

Ground state of excitons and charged excitons in a quantum well

A variational calculation of the ground state of a neutral exciton and of positively and negatively charged excitons (trions) in single quantum well is presented. We study the dependance of the correlation energy and of the binding energy on the well width and on the hole mass. Our results are are compared with previous theoretical results and with avalaible experimental data.Comment: 8 pages, 5 figures presented to OECS

Acceptor Raman scattering in GaAs-AlxGa1-xAs quantum-well structures

We report resonant Raman scattering from Be acceptors in GaAs-AlxGa1-xAs quantum well structures, grown by molecular beam epitaxy. Center- and edge-doped samples with well widths in the range 70-165 A were investigated as a function of temperature and uniaxial stress. The data show confinement-induced shifts and splittings of the lowest-lying acceptor levels in good agreement with recent calculations, and also excitations that may involve impurity states derived from higher subbands. The stress dependence of the spectra reveals coupling of the lowest acceptor transition to transverse acoustic phonons. Confinement-split lines exhibit a not fully understood intensity exchange with increasing temperature.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26808/1/0000364.pd

Enhanced and quenched Raman scattering by interface phonons in semiconductor superlattices: What are the defects?

We report on the magnetic field and power density dependences of resonant Raman scattering by interface phonons in GaAs---AlxGa1-xAs superlattices. Strong photoexcitation leads to quenching of the nominally forbidden (and sample-dependent) scattering while a dramatic enhancement of the intensity is observed in the presence of a magnetic field. Alternative mechanisms that partially account for the experimental findings are discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/27561/1/0000605.pd

Валовой региональный продукт Гомельской области: специфика формирования и пути повышения

Представлен анализ динамики развития промышленности Гомельской области в 2005–2010 гг. Рассмотрена сущность категории «валовой региональный продукт». Дан сравнительный анализ динамики этого показателя в Гомельской области за первое полугодие 2011 г., приведена оценка специфики его формирования и рассмотрены пути его повышения.The analysis of Gomel region development dynamics in 2005–2010 is presented. The nature of “gross regional product” category is considered. Comparative analysis of the dynamics of this index in Gomel region for the first half of the year 2011 is conducted. Evaluation of specific features of its formation is presented and the ways of its increasing are considered

Reliability characteristics and conduction mechanisms in resistive switching memory devices using ZnO thin films

In this work, bipolar resistive switching characteristics were demonstrated in the Pt/ZnO/Pt structure. Reliability tests show that ac cycling endurance level above 106 can be achieved. However, significant window closure takes place after about 102 dc cycles. Data retention characteristic exhibits no observed degradation after 168 h. Read durability shows stable resistance states after 106 read times. The current transportation in ZnO films is dominated by the hopping conduction and the ohmic conduction in high-resistance and low-resistance states, respectively. Therefore, the electrical parameters of trap energy level, trap spacing, Fermi level, electron mobility, and effective density of states in conduction band in ZnO were identified

Investigation of cracks in GaN films grown by combined hydride and metal organic vapor-phase epitaxial method

Cracks appeared in GaN epitaxial layers which were grown by a novel method combining metal organic vapor-phase epitaxy (MOCVD) and hydride vapor-phase epitaxy (HVPE) in one chamber. The origin of cracks in a 22-μm thick GaN film was fully investigated by high-resolution X-ray diffraction (XRD), micro-Raman spectra, and scanning electron microscopy (SEM). Many cracks under the surface were first observed by SEM after etching for 10 min. By investigating the cross section of the sample with high-resolution micro-Raman spectra, the distribution of the stress along the depth was determined. From the interface of the film/substrate to the top surface of the film, several turnings were found. A large compressive stress existed at the interface. The stress went down as the detecting area was moved up from the interface to the overlayer, and it was maintained at a large value for a long depth area. Then it went down again, and it finally increased near the top surface. The cross-section of the film was observed after cleaving and etching for 2 min. It was found that the crystal quality of the healed part was nearly the same as the uncracked region. This indicated that cracking occurred in the growth, when the tensile stress accumulated and reached the critical value. Moreover, the cracks would heal because of high lateral growth rate