Anomalous temperature dependence of photoluminescence from a-C : H film deposited by energetic hydrocarbon ion beam

The temperature dependence of photoluminescence (PL) from a-C:H film deposited by CH3+ ion beam has been performed and an anomalous behavior has been reported. A transition temperature at which the PL intensity, peak position and full width at the half maximum change sharply was observed. It is proposed that different structure units. at least three, are responsible for such behavior. Above the transition point. increasing temperature will lead to the dominance of non-radiative recombination process, which quenches the PL overall and preferentially the red part, Possible emission mechanisms have been discussed. (C) 2002 Elsevier Science Ltd. All rights reserved.

Polarity dependence of hexagonal inclusions and cubic twins in GaN/GaAs(001) epilayers measured by conventional X-ray pole figure and grazing incident diffraction pole figure

The distribution of mixed phases and its dependence on the polarity of cubic GaN epilayers are investigated by conventional X-ray pole figure and grazing incident diffraction (GID) pole figure. The hexagonal inclusions and cubic twins can be classified into two portions: one is formed with strict crystalline orientations, the other with crystalline misorientations. The former can be measured by conventional pole figures which reveal that the density of lamellate hexagonal grains and cubic twins located on (1 1 1)(Ga) and ((1) over bar (1) over bar1)(Ga) along [1 (1) over bar 0] direction are higher than those on ((1) over bar 1 1), and (1 (1) over bar 1)(N) along [110] direction. However, the low signals from tiny mixed phases with crystalline misorientations, detected by GID pole figures, distribute in a larger phi region near the [1 1 0] and [(1) over bar (1) over bar 0] directions with much weaker intensity, and in a smaller phi region near the [1 (1) over bar 0] and [(1) over bar 1 0] directions with slightly stronger intensity. (C) 2001 Elsevier Science B.V. All rights reserved.

Polarity dependence of hexagonal GaN films on two opposite c faces of Al2O3 substrate

GaN films were grown in pairs on two opposite c faces of Al2O3 substrate by low-pressure metal-organic vapor phase epitaxy, and studied by scanning electron microscopy and converged beam electron diffraction. It is found that GaN film on the c-Al2O3 whose c face is forward to its crystal seed has [0001] polarity, and the other film on the C-Al2O3 whose c face is backward to its crystal seed has [000 (1) over bar] polarity. (C) 2001 American Institute of Physics.

Substrate dependence of InGaAs quantum dots grown by molecular beam epitaxy

A systematic study of self-organized In0.5Ga0.5As quantum dots (QDs) and islands grown by molecular beam epitaxy on (100) and (n11) A/B GaAs substrates is given, where n varies from 1 to 5. Low-temperature photoluminescence results show that the properties of the dots have a strong dependence on the substrate orientation as revealed by atomic force microscopy, consistent with the differences in size, shape, and distribution of QDs on different substrates. From (100) to (111) surface, the photoluminescence peak position of dots on B surfaces is found to blueshift more than that on A surfaces. QDs are also formed on (511) A surface. The positional distribution of these dots exhibits a wavy shape, which is related to the corrugated structure of this surface. Two kinds of islands are formed on (111) A surface, but further work is needed to explain the mechanism of these islands. (C) 2001 American Vacuum Society.

Strong temperature dependence of photoluminescence properties in visible InAlAs quantum dots

Strong temperature dependence of optical properties has been studied in visible InAlAs/AlGaAs quantum dots, by employing photoluminescence (PL) and time-resolved photoluminescence (TRPL) measurements. The fast redshift of the exciton emission peak was observed at much lower temperature range compared to that observed in the InAs/GaAs QDs. In TRPL we did not observe the constant decay time even at low temperature. Instead, the observed decay time increases quickly with increasing temperature, showing 2D properties in the transient dynamic process. We attributed our results to the strong lateral coupling effect, which results in the formation of the local minibands or extended states from the discrete energy levels. (C) 2000 Elsevier Science B.V. All rights reserved.

Temperature dependence of electron redistribution in modulation-doped InAs/GaAs quantum dots

In this work we report the photoluminescence (PL) and interband absorption study of Si-modulation-doped multilayer InAs/GaAs quantum dots grown by molecular beam epitaxy (MBE) on (100) oriented GaAs substrates. Low-temperature PL shows a distinctive double-peak feature. Power-dependent PL and transmission electron microscopy (TEM) confirm that they stem from the ground states emission of islands of bimodal size distribution. Temperature-dependent PL study indicates that the family of small dots is ensemble effect dominated while the family of large dots is likely to be dominated by the intrinsic property of single quantum dots (QDs). The temperature-dependent PL and interband absorption measurements are discussed in terms of thermalized redistribution of the carriers among groups of QDs of different sizes in the ensemble. (C) 2000 Elsevier Science B.V. All rights reserved.

Pressure dependence of Mn2+ fluorescence in ZnS : Mn2+ nanoparticles

The photoluminescence of Mn2+ in ZnS:Mn2+ nanoparticles with an average size of 4.5 nm has been measured under hydrostatic pressure from 0 to 6 GPa. The emission position is red-shifted at a rate of -33.3+/-0.6meV/GPa, which is in good agreement with the calculated value of -30.4meV/GPa using the crystal field theory. (C) 2000 Elsevier Science B.V. All rights reserved.

Temperature dependence of polaron cyclotron resonance mass in GaAs/AlGaAs heterostructures

The temperature dependence of polaron cyclotron resonance mass in GaAs/AlGaAs heterostructures is reinvestigated theoretically. By taking into account the electron-longitudinal-optic phonon interaction with temperature-dependent many-body effects, the conduction band non-parabolicity, and the influence of nonzero magnetic field, a good agreement with experiment is obtained.

Temperature dependence of photoluminescence of an n-i-p-i GaAs superlattice

Both the photoluminescence peaks corresponding to the vertical transitions and the nonvertical transitions in an n-i-p-i GaAs superlattice are clearly observed. The redshifts of the two peaks with increasing temperature are: discussed in terms of the temperature-dependent carrier separation effect.

Anomalous temperature dependence of photoluminescence from InAs quantum dots

Self-assembled InAs quantum dots are fabricated on a GaAs substrate by molecular beam epitaxy. The dots are covered by several monolayers of In0.2Ga0.8As before a GaAs cap layer and an in situ postgrowth annealing is performed to tune the emission to higher energy. The temperature dependence of photoluminescence from this structure demonstrates a slower redshift rate of the peak position, a gradual broadening of the linewidth and an abnormal enhancement of integrated intensity as the temperature is increased from 15 to 300 K. These phenomena are closely related to the introduction of an InGaAs layer and to the intermixing of In and Ga atoms during annealing. We propose a model to explain the unusual increase in PL intensity, which fits the experimental data well. (C) 2000 American Institute of Physics. [S0021-8979(00)04618-1].

Temperature and excitation power dependence of the optical properties of InAs self-assembled quantum dots grown between two Al0.5Ga0.5As confining layers

We have investigated the temperature and excitation power dependence of photoluminescence properties of InAs self-assembled quantum dots grown between two Al0.5Ga0.5As quantum wells. The temperature evolutions of the lower-and higher-energy transition in the photoluminescence spectra have been observed. The striking result is that a higher-energy peak appears at 105 K and its relative intensity increases with temperature in the 105-291 K range. We demonstrate that the higher-energy peak corresponds to the excited-state transition involving the bound-electron state of quantum dots and the two-dimensional hole continuum of wetting layer. At higher temperature, the carrier transition associated with the wetting layer dominates the photoluminescence spectra. A thermalization model is given to explain the process of hole thermal transfer between wetting layer and quantum dots. (C) 2000 Published by Elsevier Science B.V. All rights reserved.

Temperature dependence of the optical properties of InAs/GaAs self-organized quantum dots with bimodal size distribution

In this work we report the optical and microscopic properties of self-organized InAs/GaAs quantum dots grown by molecular beam epitaxy on (1 0 0) oriented GaAs substrates. A distinctive double-peak feature of the PL spectra from quantum dots has been observed, and a bimodal distribution of dot sizes has also been confirmed by scanning tunneling microscopy (STM) image for uncapped sample. The power-dependent photoluminescence (PL) study demonstrates that the distinctive PL emission peaks are associated with the ground-state emission of islands in different size branches. The temperature-dependent PL study shows that the PL quenching temperature for different dot families is different. It is shown that the coupling between quantum dots plays a key role in unusual temperature dependence of QD photoluminescence. In addition, we have tuned the emission wavelength of InAs QDs to 1.3 mu m at room temperature. (C) 2000 Elsevier Science B.V. All rights reserved.

Indium composition dependence of the size uniformity of InGaAs quantum dots on (311)B GaAs grown by molecular beam epitaxy

The deposition of InxGa1-xAs (0.2 less than or equal to x less than or equal to 0.5) on (311)B GaAs surfaces using solid source molecular beam epitaxy (MBE) has been studied. Both AFM and photoluminescence emission showed that homogeneous quantum dots could be formed on (311)B GaAs surface when indium composition was around 0.4. Indium composition had a strong influence on the size uniformity and the lateral alignment of quantum dots. Compared with other surface orientation, (100) and (n11) A/B (n=1,2,3), photoluminescence measurement confirmed that (311)B surface is the most advantageous in fabricating uniform and dense quantum dots.

In composition dependence of lateral ordering in InGaAs quantum dots grown on (311)B GaAs substrates

Self-assembled InxGa1-xAs quantum dots (QDs) on (311)A/B GaAs surfaces have been grown by molecular beam epitaxy (MBE). Spontaneously ordering alignment of InxGa1-xAs with lower In content around 0.3 have been observed. The direction of alignment orientation of the QDs formation differs from the direction of misorientation of the (311)B surface, and is strongly dependent upon the In content x. The ordering alignment become significantly deteriorated as the In content is increased to above 0.5 or as the QDs are formed on (100) or (311)A substrates. (C) 1999 Elsevier Science B.V. All rights reserved.

The dependence of growth rate of GaN buffer layer on growth parameters by metalorganic vapor-phase epitaxy

The growth rate of GaN buffer layers on sapphire grown by metalorganic vapor-phase epitaxy (MOVPE) in an atmospheric pressure, two-channel reactor was studied. The growth rate, as measured using laser reflectance, was found to be dependent on growth temperature, molar flow rate of the sources tin this case, trimethylgallium and ammonia) and the input configuration of sources into the reactor. A model of the GaN buffer layer growth process by MOVPE is proposed to interpret the experimental evidence. (C) 1998 Elsevier Science B.V. All rights reserved.