We report optical and structural characterizations of InAs quantum dot superlattices grown by molecular beam epitaxy on GaAs (001). Cross-sectional electron microscopy imaging reveals ~ 20 nm ...diameter InAs islands well aligned along the growth direction. Low temperature photoluminescence spectra exhibit a clear redshift with decreasing island vertical separation, as a result of electronic coupling between stacked dots, given that the larger shift is obtained for 70 Å spacing. At high excitation power, the photoluminescence spectra show a doublet structure corresponding to coupled and uncoupled quantum dot states. The temperature dependence of the photoluminescence indicates that thermionic emission activation energy is much lower than the estimated barrier height. Such a difference is explained by the presence of non-radiative recombination centers due to strain relaxation and In segregation.
Changes of dark current, photocurrent under black body illumination, IR photoconductivity and IR intersubband absorption spectra caused by 3.5 MeV room-temperature electron irradiation in MBE-grown ...Si-doped GaAs/AlGaAs multiquantum-well mesa structures (with photoresponse peak at a wavelength of 8.5 gm) are investigated. The following processes were found to occur with a dose increase: (1) decreasing of the dark current in the range of two orders; (2) increasing of photocurrent-to-dark-current ratio by several times; (3) decreasing of intersubband absorption; (4) relatively slight changes in detectivity with nonmonotonical dependence versus bias voltage. However, both photoconductivity and intersubband absorption spectra shapes remained unchanged.
A qualitative interpretation of the observed phenomena is given based on the formation of radiation-induced compensating centers. It is proposed to use radiation treatments for local and overall tuning of parameters of quantum well photodetector arrays.
In the present work, the Aharonov–Bohm effect in submicron GaAs/AlGaAs ring with an in-plane ferromagnetic gate is investigated. The experiment is based on the study of the derivatives of ...magnetoresistance and microwave EMF to gate voltage. The experimental results are explained by electron wave interference in the presence of an inhomogeneous magnetic field in the ring.
We investigate the activated conductivity for Landau levels at lling factors v =1,2 in a parabolic Al xGa1-x As well down to 30 mK. We obtain a very small activation energy ~ 0.02 meV, which is ...almost 1-2 orders of magnitude smaller than the expected values for energy gaps in a wide quantum well. The resistivity minima vanish completely when a parallel component of magnetic field is applied. The collapse of the energy gaps in the wide parabolic well occurs due to the new electron correlated state, probably the charge density wave state predicted for a uniform wide electron slab in high magnetic field.
We have measured the Shubnikov de Haas (SdH) oscillations of a nonplanar two-dimensional electron gas (2DEG) fabricated by overgrowth of a GaAs/AlGaAs heterojunction on a pre-patterned substrate. ...When placed in a uniform external magnetic field B, the field normal to the nonplanar 2DEG is spatially modulated, and electrons experience a nonuniform magnetic field. In a tilted magnetic field, the SdH oscillations are much more strongly damped than in a field perpendicular to the substrate. We consider several mechanisms and conclude that the electron scattering by the magnetic field spatial uctuations plays a main role in the transport properties of a nonplanar 2DEG at low magnetic field.
Purpose: To evaluate the vision-related quality of life (VRQoL) of patients receiving hemodialysis through the assessment of the impact of vision impairment (IVI) questionnaire and ocular parameters, ...including best-corrected visual acuity (BCVA), intraocular pressure (IOP), and refraction as calculated by spherical equivalent (SE) of each eye.
Methods: Fifty-one patients with end-stage renal disease undergoing hemodialysis at a single center were recruited, and a total of 77 eyes were evaluated. BCVA, IOP, and SE were evaluated before and after hemodialysis (within 30 min).
Results: Of the 51 patients recruited, 13 (25%) were female, 37 (73%) were male, and one (2%) chose not to specify gender. The mean age was 61.85 ± 32 years. The mobility IVI score was correlated significantly with the presence of hypertension (P = 0.01), eye drop usage (P = 0.04), and gender (P = 0.04). Emotional IVI scores were correlated significantly with diabetes (P = 0.03) and hypertension (P < 0.01). IOP significantly correlated with the IVI overall score (P = 0.02), including the reading IVI subscale and the emotional IVI subscale. Several factors were associated with posthemodialysis ocular parameters, including predialysis ocular parameters, age, and hypertension (P < 0.05 for all).
Conclusions: IOP significantly correlated with VRQoL in hemodialysis patients. Demographic variables such as diabetes status, hypertension, eye drop usage, and gender also significantly correlated with subsections of the IVI questionnaire. This study investigated the relationship between ocular parameters and VRQoL in hemodialysis patients, and future longitudinal research is needed to further elucidate the mechanisms.
InAs/GaAs strained-layer superlattices (SLS) grown on a GaAs(100)
substrate were studied by both Raman spectroscopy (RS) and transmission
electron microscopy (TEM). It was shown that the interfaces ...inside the
superlattice are coherent, but the superlattice–substrate interface
contain an orthogonal two-dimensional network of 60° misfit
dislocations. Using these experimental data values of elastic strain in
individual layers and the average values of the residual elastic strain in SLS
were determined. The latter are approximately one order of magnitude higher
than theoretically predicted data, which suggests that the relaxation of
elastic strains was not fully complete. Subsequent annealing of these
structures led to the generation of more misfit dislocations, consistent with
further relaxation of elastic strain.
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