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1.
An efficient analytical model to calculate the optical gain of the quantum-well laser of the GaN–In x Ga1?x N material system is used in this paper. Based on the anisotropic effective mass theories, empirical formulas delineating the relations between optical gain, emission wavelength, well width and material compositions are obtained for such a quantum-well lasers.  相似文献   

2.
It has been shown elsewhere that the room temperature yield pressure of In x Ga1? x As superlattices measured by nanoindentation, decreases from a high value as the volume averaged strain modulation is increased, while at 500°C under uniaxial compression or tension the yield stress increases from a low value with increasing strain modulation. We have used cross-sectional transmission electron microscopy to examine the deformation mechanisms in these two loading regimes. At room temperature both twinning and dislocation flow was found with the proportion of twinning decreasing with increasing strain modulation. The coherency strain of the superlattice is retained in a twin but partially relaxed by dislocation flow. The strain energy released by the loss of coherency assists dislocation flow and weakens the superlattice. Twins are only nucleated when a critical elastic shear of about 7° is achieved at the surface. The plastic zone dimensions under the indent are finite at the yield point, with a width and depth of approximately 1.3?µm and 1.1?µm respectively. Under uniaxial compression and tension at 500°C the superlattices deform by dislocation flow along {111} planes. The most highly strained samples also partially relax through the formation of misfit dislocations.  相似文献   

3.
In(Ga)As/GaAs quantum-dot (QD) lasers with emission wavelength at 1295 nm at room temperature are fabricated. The laser active region contains a threefold stack of QD layers with surface dot density of 4.56 × 1010 cm–2. The laser structure is aluminum-free with InGaP as cladding layers. Threshold current density of a narrow stripe laser of 8 m wide and 3.5 mm long is 152.5 A/cm2. The highest relaxation oscillation frequency measured at room temperature is 1.8 GHz, corresponding to a modulation bandwidth of 2.8 GHz due to the small damping factor. From the above measurement, the differential gain and gain compression factor were extracted to be 4.3 × 10–16 cm2 and 3.4 × 10 –17 cm 3, respectively. Using these parameters, the maximum modulation bandwidth f 3 dB max is estimated as 7.9 GHz.  相似文献   

4.
Zhang  Y.-J.  Zhu  L.  Gao  Z.-G.  Chen  M.-H.  Dong  Y.  Xie  S.-Z. 《Optical and Quantum Electronics》2003,35(9):879-886
It is well known that complex rate equations and the couple wave equation have to be solved by the method of iteration in the simulation of multi-quantum well (MQW) distributed feedback Bragg (DFB) lasers, and a long CPU time is needed. In this paper, from the oscillation condition of lasers, we propose a simple and fast model for optimization of In1–xy Ga y Al x As strained MQW DFB lasers. The well number and the cavity length of 1.55 m wavelength In1–xy Ga y Al x As MQW DFB lasers are optimized using the model. As a result, the simple model gives almost the same results as the complex one, but 90% CPU time can be saved. In addition, a low threshold, high maximum operating temperature of 550–560 K, and high relaxation oscillation frequency of over 30 GHz MQW DFB laser is presented.  相似文献   

5.
Previous studies of phase transformation and superconductivity on LaAg under pressure are extended to further CsCl-compounds LaAg0.5In0.5, LaCd, and LaZn. The cubic-totetragonal transition temperatureT M in LaAg0.5In0.5 and LaCd increases rapidly with pressure, whereas LaZn does not transform to 16 kbar. The present results are used to correct the dependence ofT M onx in LaAg x In1–x to constant volume; the bell-shaped curveT M (x) with maximum atx0.5 is thereby corrected to one whereT M rises steeply with In concentration across the entire range. A possible correlation between the magnitude ofT M and the extent ofd-band occupation is inferred. Above 1.17 K only LaZn is found to be superconducting withT c (0)=1.65 K;T c (P) passes through a shallow minimum at 6 kbar.  相似文献   

6.
7.
Strain effects on a built-in electron-hole dipole moment are investigated in asymmetric In x Ga1?x As coupled quantum dots. We compute electron-hole separation as a function of alloy compositions for both electron and hole resonance cases. It is noted that the inclusion of strain enhances the built-in dipole moments and that the inverted electron-hole alignment is found for electron and hole resonances. Furthermore, the reversal of dipole moments gives rise to different asymmetric Stark shifts in each transition spectrum.  相似文献   

8.
The influence of the mask material used for formation of GaN mesa-structures using plasma-chemical etching in a BCl3 : Ar : N2 atmosphere is studied. It is shown that a bilayer SiO2/Cr mask in which the thickness of the chromium layer is six to seven times smaller than a desired etch depth provides effective protection of the surface and allows the formation of structures with a flat surface for an etch depth of up to 2.5 μm. When the mask is produced by conventional lithography, the slope of the side walls is no more than 10° and decreases when liftoff lithography is applied.  相似文献   

9.
Atomistic simulations are used in combination with the two potential energy functions, namely, the Valence Force Field (VFF) model and the Tersoff model, to study the solution thermodynamics of In x Ga1?x As alloy. The simulation data, in the form of a T ? x diagram, is contrasted with the results obtained by using the Ho and Stringfellow approach. It is observed that for the VFF model, the upper critical solution temperature obtained from simulation data is approximately 850 K, which is higher than the 729 K predicted by the Ho and Stringfellow treatment. The composition range for which the two-phase heterogeneous region exists is wider than that predicted by the Ho and Stringfellow approach. The Tersoff model predicts a complex miscibility diagram, where the 850 K temperature corresponds to the approximate ‘eutectic’ temperature. Further improvement of model predictions may be made possible by investigation of temperature and composition dependent interaction parameter in a modified regular solution theory, and investigation of non-random, non-ideal solution models in the Ho and Stringfellow treatment, development of temperature dependent VFF model parameters and adjustment of Tersoff model parameters to account for longer range interactions which exist at temperatures above 850 K. The miscibility diagram constructed using the Tersoff model simulation data can be used to provide information on the phase stability and equilibrium Indium content at any given temperature for the crystalline solid solution.  相似文献   

10.
宋斌  凌俐  曹培林 《中国物理》2004,13(4):489-496
The structures of Ga_3N, GaN_3, Ga_3N_2 and Ga_2N_3 clusters are studied using the full-potential linear-muffin-tin-orbital molecular dynamics (FP-LMTO MD) method. Four structures for Ga_3 N, five structures for GaN_3, nine structures for Ga_3N_2 and nine structures for Ga_2N_3 have been obtained. The most stable structures of these clusters are planar ones. A strong dominance of the N--N bond over the Ga--N and Ga--Ga bonds appears to control the structural skeletons, supporting the previous result obtained by Kandalam and co-workers. The most stable structures of these small GaN clusters displayed semiconductor-like properties through the calculation of the HOMO-LUMO gaps.  相似文献   

11.
Nanostructuring of the Ge0.99Mn0.01 single-crystal alloy with the formation of nanowires 60 nm in diameter has been revealed to bring about an increase in the temperature of the percolation transition to the ferromagnetic state to T C1 ≈ 45 K and a broadening of the distribution of Curie temperatures in Ge n Mn m clusters T C2 ≈ 125?270 K as compared to Ge0.98Mn0.02 thin single-crystal films for which T C1 ≈ 6 K and T C2 ≈ 270 K.  相似文献   

12.
The single crystals of tin monosulphoselenides in the form of a series SnS x Se1?x (where x?=?0, 0.25, 0.50,0.75 and 1) have been grown using the direct vapor transport technique (DVT). The analysis of the X-ray diffraction patterns reveals that all crystals belong to the orthorhombic crystal structure. Hall effect measurements were carried out on grown crystals at room temperature. The optical absorption measurements at room temperature have been carried out for all crystals. The values of the band gap were determined at atmospheric pressure and also calculated at high-pressure. Simultaneous thermoelectric power (TEP) and a.c. resistance measurements up to 8?GPa were carried out. The results of the effect of high-pressure on the electrical resistance of the grown crystals are reported in this paper.  相似文献   

13.
The present work focuses on the structural, optical, and electrical properties of Zn1?x Cd x Se (0.1≤x≤0.25) compounds. The compounds were synthesized by solid state reaction. X-ray diffraction (XRD) patterns confirm that the samples have cubic single phase (zinc-blende) crystal structure with space group F-43m. The crystal structural parameters were refined by the Rietveld method using the FullProf program. It was found that the lattice parameters increase linearly with increasing the Cd content and obeys Vegard’s law. The refined values of the crystallite size and the bond lengths increase with increasing the Cd content. The energy band gap of the samples has been calculated and it was found that it decreased as Cd increased. The conductivity of the samples increases with increasing both of composition parameter x and temperature, and showing semiconducting behavior.  相似文献   

14.
Abstract

We present a quantitative k.P Hamiltonian which describes analytically the composition dependence of the energy gap, interband momentum matrix element, band edge effective masses and conduction band dispersion of GaNXAs1?x alloys for low N concentrations (x < ~ 0.05). The model has been confirmed using an sp3s? tight-binding Hamiltonian whose results agree well both with experiment and with previous pseudopotential calculations. The model should be of wide use to guide the future development of this material system and its applications.  相似文献   

15.
16.
The magnetic and thermoelastic martensitic transformations and physical properties (magnetization, electrical resistivity, thermoelectric power, relative elongation, and thermal expansion coefficient) of multicomponent magnetic shape memory alloys Ni50 ? x Co x Mn29Ga21 (x = 0, 1, 2, 3, 10 at %) have been investigated. The critical temperatures of thermoelastic martensitic transformation and magnetic transitions have been determined. It has been found that the alloy with 10 at % Co undergoes a martensitic transformation in the temperature range of 6–10 K.  相似文献   

17.
The structural state of a Zn1 ? x Fe x Se (x = 0.001) crystal has been studied using thermal neutron diffraction. The diffraction patterns of the cubic crystal have been found to contain diffuse scattering regions concentrated in the vicinity of the strong Bragg reflections. It has been shown that the diffuse scattering effects are due to local transverse displacements of the crystal lattice atoms, and these displacements are induced by iron ions that demonstrate the static Jahn-Teller effect of the tetragonal type in the ZnSe compound.  相似文献   

18.
Samples of the (Fe70Al30)100???x Ni x system, with x?=?5, 10, 15, and 20, were prepared by mechanical alloying using milling times of 12, 24, 36, 48, and 72 h and characterized by X-ray diffraction (XRD) and Mössbauer spectrometry (MS). XRD of all the samples allowed us to identify the BCC structure as the main component. A decreasing lattice parameter, as the milling time and Ni content increase, was obtained. The MS experiments were carried out at room temperature. The spectra were fitted with a hyperfine magnetic field distribution (HMFD). The Mean Hyperfine Fields (MHF) are ranged between 27 and 29 T with a small dependence with the milling time and was not strongly influenced by Ni content. An additional paramagnetic single line in the spectra of samples with x?=?20 and that of sample with x?=?15 and milled during 72 h must be included. The Mössbauer spectral area of this phase increases when the milling time increases and it was associated to an FCC phase.  相似文献   

19.
The effect of an invertedp-region along the free surface ofn-Al x Ga1−x Sb on the reverse current ofp−n structures from the given solid solution is analyzed. Expressions which describe “collection” of the inverted layer current on the cylindrical surface of ann-region are discussed. The contribution of the near-surface and bulk components to the reverse current ofp−n structures with a semi-infiniten-region is estimated. For structures with a two-layern-region of finite thickness we have calculated the dependence of the near-surface current on the voltage across thep−n structure, the thickness of then-region, and its composition and doping level. We have compared the calculated current-voltage characteristics with experiment using a Al0.15Ga0.85Sbp−n structure as an example. Tomsk State University, Tomsk. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, Vol. 42, No. 1, pp. 34–40, January, 1999.  相似文献   

20.
The surface of CuInSe2 or related compounds is an essential part of heterojunctions for photovoltaic applications. It is generally accepted that the reconstruction of the surface of slightly Cu-deficient film results in a Cu-depleted defect layer. Since this surface layer generally exhibits a CuIn3Se5 stoichiometry the existence of a defect chalcopyrite phase CuIn3Se5 has also been proposed. Although efforts have been made to identify this phase structurally by means of grazing incidence X-ray-diffraction (GIXRD), it has not been detected so far. However, the existence of a Cu-depleted surface layer fits well in the existing theory, which models the functioning of photovoltaic devices. In this contribution we present for the first time evidence for a Cu-depleted surface layer measured by X-ray diffraction. A careful analysis of GIXRD-data at incident angles from 0.3 to 10° by comparing the measured shape and width with simulated spectra confirms structural changes in the surface layer. The thickness of this layer varies from 5 to 60 nm with the integral Cu-content of the film. Hence GIXRD provides a unique means for non-destructive depth profiling.  相似文献   

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