Room temperature spin relaxation in GaAs/AlGaAs multiple quantum wells

We have explored the dependence of electron spin relaxation in undoped GaAs/AlGaAs quantum wells on well width (confinement energy) at 300 K. For wide wells, the relaxation rate tends to the intrinsic bulk value due to the D'yakonov-Perel (DP) mechanism with momentum scattering by phonons. In narrower wells, there is a strong dependence of relaxation rate on well width, as expected for the DP mechanism, but also considerable variation between samples from different sources, which we attribute to differences in sample interface morphology. (C) 1998 American Institute of Physics. [S0003-6951(98)02541-8].</p

Pulsed laser deposition of Ga-La-S chalcogenide glass thin film optical waveguides

Thin film optical waveguides of the chalcogenide glass Ga-La-S have been deposited on substrates of CaF2 and microscope glass by the technique of pulsed laser deposition. The chalcogenide properties of photobleaching, photodoping, and photoinduced refractive index changes have been observed and preliminary experiments carried out. The refractive index and thickness of the layer were verified using a waveguide "dark mode" analysis technique

Exciton spin dynamics in quantum wells

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Spin relaxation in GaAs/AlxGa1-xAs quantum wells

Spin dynamics of photoexcited carriers in GaAs/AlxGa1-xAs quantum wells have been investigated in a wafer containing twelve different single quantum wells, allowing full investigation of well-width and temperature dependences with minimal accidental variations due to growth conditions. The behavior at low temperatures is dominated by excitonic effects, confirming results described in detail by others. Between 50 and 90 K there is a transition from excitonic to free-carrier-dominated behavior; both the temperature and time scale of the transition are in excellent agreement with a theoretical model for exciton dissociation. Above 90 K we find two-component spin decays consisting of an unresolved component (faster than 2 ps) associated with exciton dissociation and hole spin-relaxation and a longer-lived component that yields the electron spin-relaxation time. In the free-carrier regime, the electron spin-relaxation rate in wide wells follows that for bulk GaAs, which varies approximately as T2. For narrow wells the rate is approximately independent of temperature and varies quadratically with confinement energy. This behavior is consistent with dominance of the D'yakonov-Perel mechanism of electron-spin relaxation and the expected behavior of the electron mobility. The data show evidence of the influence of electron scattering by interface roughness

Pulsed-laser deposition of Ga-La-S chalcogenide glass films for optical waveguide applications

Thin films of Ga-La-S chalcogenide glass have been ablatively deposited onto a range of substrates, including CaF2, and microscope cover slips. The resultant films are deficient in their sulphur composition by approximately 25%, when compared to the bulk targets used, but the interesting chalcogenide photostructural effects are not compromised by this deficiency. Experiments so far have established that photorefractive effects, such as photodoping, photobleaching and grating formation. all occur readily in the thin films, and gratings have been written using laser and e-beam addressing, to create diffractive structures for optical waveguide applications

Two-Dimensional Transverse Cross-Section Nanopotentiometry of Actively-Driven Buried Heterostructure Multiple-Quantum-Well Lasers

We report results of two-dimensional local potential measurement of the transverse cross-section of operating buried-heterostructure (BH) multiple-quantum-well lasers. The measured two-dimensional image of potential distribution resolved clearly the multiquantum-well active region and the p-n-p-n current-blocking structure of the BH laser, showing close correlation to the scanning spreading resistancemicroscopy image. Nanopotentiometry measurements were also performed on the p-n-p-n current-blocking structure of a BH laser under different forward bias voltages. The nanopotentiometry results provide direct insight into the behavior of p-n-p-n current-blocking layers intended to minimize current leakage. Our results demonstrate the application of nanopotentiometry to the delineation of complex buried structures in quantum optoelectronic devices

Two-dimensional profiling of carriers in a buried heterostructure multi-quantum-well laser: Calibrated scanning spreading resistance microscopy and scanning capacitance microscopy

We report results of a scanning spreading resistancemicroscopy (SSRM) and scanning capacitancemicroscopy (SCM) study of the distribution of charge carriers inside multi-quantum-well (MQW) buried heterostructure (BH) lasers. We demonstrate that individual quantum-well–barrier layers can be resolved using high-resolution SSRM. Calibrated SSRM and SCM measurements were performed on the MQW BH laser structure, by utilizing known InP dopant staircase samples to calibrate the instrumentation. Doping concentrations derived from SSRM and SCM measurements were compared with the nominal values of both p- and n-doped regions in the MQW BH lasers. For n-type materials, the accuracy was bias dependent with SSRM, while for SCM, excellent quantitative agreement between measured and nominal dopant values was obtained. The SSRM was able to measure the dopant concentration in the p-type materials with ∼30% accuracy, but quantitative measurements could not be obtained with the SCM. Our results demonstrate the utility of combining calibrated SSRM and SCM to delineate quantitatively the transverse cross-sectional structure of complex two-dimensional devices such as MQW BH lasers, in which traditional one-dimensional probing using secondary ion mass spectroscopy provides only a partial picture of internal device structure