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Room-temperature (RT) continuous-wave (CW) performance of modern 1300-nm oxide-confined In(Ga)As/GaAs quantum-dot (QD) vertical-cavity
surface-emitting diode lasers (VCSELs) taking advantage of many QD sheets is investigated using our comprehensive self-consistent
simulation model to suggest their optimal design. Obviously, quantum dots should be as uniform as possible and as dense as
possible to ensure high enough optical gain. Besides, our simulation reveals that efficient and uniform current injection
into VCSEL active regions necessary to enhance excitation of the desired fundamental LP01 mode is accomplished in the VCSEL configuration with the broad-area bottom contact and the ring upper one as well as with
the oxide aperture localized within the first period of the upper p-type DBR. The doping of the DBR mirrors is chosen as a
compromise between their high enough electrical conductivity and low enough free-carrier absorption. The oxide aperture is
additionally introducing the radial optical waveguiding. Moreover, our analysis has been concluded that VCSEL active regions
should be composed of at least 9 QD sheets to acquire efficient RT CW operation. Furthermore, rather longer optical cavities
are recommended in this case because localization of QD sheets should be adjusted to the anti-node positions of the optical
cavity standing wave. 相似文献
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Robert P. Sarzała Łukasz Piskorski Robert Kudrawiec Włodzmierz Nakwaski 《Applied Physics A: Materials Science & Processing》2014,115(3):961-969
In the present paper, a comprehensive computer simulation is used to determine optimal structure of the InP-based GaInNAs quantum-well (QW) active region and to investigate a possibility of reaching room-temperature (RT) continuous-wave (CW) single-fundamental-mode 2.33-μm operation of vertical-cavity surface-emitting laser (VCSEL) with such an active region. From among various considered InP-based active regions, the one with the Ga0.15In0.85N0.015As0.985/Al0.138Ga0.332In0.530As QW, i.e. with barriers lattice matched to InP, seems to be optimal for the 2.33-μm VCSEL performance. Its QW material is chosen for the required long-wavelength emission whereas its barrier is expected to ensure promising laser performance at room and higher temperatures. The latter is mostly connected with the QW conduction band offset equal in the above active region to as much as 413 meV, which is much larger than those of its possible lattice matched to InP competitors, e.g. 276 meV for the Ga0.47In0.53As barrier and 346 meV for the Ga0.327In0.673As0.71P0.29 one. Our simulation reveals that from among various considered structures, a VCSEL with a 4-μm-diameter tunnel junction and two 6-nm Ga0.15In0.85N0.015As0.985/Al0.138Ga0.332In0.530As QWs exhibits the lowest calculated threshold current of 0.88 mA. Its promising RT CW performance suggests that it may represent a very interesting alternative to GaSb-based VCSELs. 相似文献
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CoFe2O4-BaTiO3 composites were prepared using conventional ceramic double sintering process with various compositions. Presence of two phases
in the composites was confirmed using X-ray diffraction. The dc resistivity and thermoemf as a function of temperature in
the temperature range 300 K to 600 K were measured. Variation of dielectric constant (ɛ′) with frequency in the range 100 Hz to 1 MHz and also with temperature at a fixed frequency of 1 kHz was studied. The ac
conductivity was derived from dielectric constant (ɛ′) and loss tangent (tan δ). The nature of conduction is discussed on the basis of small polaron hopping model. The static value of magnetoelectric
conversion factor has been studied as a function of magnetic field. 相似文献
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Harmer J Finazzo C Piskorski R Ebner S Duin EC Goenrich M Thauer RK Reiher M Schweiger A Hinderberger D Jaun B 《Journal of the American Chemical Society》2008,130(33):10907-10920
Methanogenic archaea utilize a specific pathway in their metabolism, converting C1 substrates (i.e., CO2) or acetate to methane and thereby providing energy for the cell. Methyl-coenzyme M reductase (MCR) catalyzes the key step in the process, namely methyl-coenzyme M (CH3-S-CoM) plus coenzyme B (HS-CoB) to methane and CoM-S-S-CoB. The active site of MCR contains the nickel porphinoid F430. We report here on the coordinated ligands of the two paramagnetic MCR red2 states, induced when HS-CoM (a reversible competitive inhibitor) and the second substrate HS-CoB or its analogue CH3-S-CoB are added to the enzyme in the active MCR red1 state (Ni(I)F430). Continuous wave and pulse EPR spectroscopy are used to show that the MCR red2a state exhibits a very large proton hyperfine interaction with principal values A((1)H) = [-43,-42,-5] MHz and thus represents formally a Ni(III)F430 hydride complex formed by oxidative addition to Ni(I). In view of the known ability of nickel hydrides to activate methane, and the growing body of evidence for the involvement of MCR in "reverse" methanogenesis (anaerobic oxidation of methane), we believe that the nickel hydride complex reported here could play a key role in helping to understand both the mechanism of "reverse" and "forward" methanogenesis. 相似文献
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Robert P. Sarzała Łukasz Piskorski 《Applied Physics A: Materials Science & Processing》2011,102(2):359-366
The comprehensive optical-electrical-thermal-recombination self-consistent VCSEL model is used to compare the performance
of oxide-confined (OC) and proton-implanted (PI) VCSELs and to optimise their structures. Generally index-guided (IG) OC VCSELs
demonstrate lower lasing thresholds whereas both gain-guided (GG) OC and PI ones manifest much better mode selectivity. Therefore,
their either low-threshold IG or mode-selective GG versions may be intentionally used for different VCSEL applications. Lasing
thresholds of OC IG VCSELs have been found to be very sensitive to the exact localisation of their thin oxide apertures, which
should be shifted as close as possible towards the anti-node position. PI VCSELs, on the other hand, are simpler and cheaper
in their manufacturing than OC ones. Although lower threshold currents are manifested by PI VCSELs with very thick implanted
regions, lower threshold powers are achieved in these devices with much thicker upper unaffected layer used for the radial
current flow from the ring contact towards the laser axis. Paradoxically poor thermal properties of PI VCSELs enable lower
lasing thresholds of slightly detuned devices. To conclude, cheaper and mode-selective PI VCSELs may be used instead of OC
ones in many of their applications provided ambient temperatures and laser outputs are not too high. 相似文献
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MOS capacitors were fabricated on 3C-SiC n-type substrate (001) with a 10-μm N-type epitaxial layer. An SiO2 layer of the thickness tOX ≈55 nm was deposited by PECVD. Circular Al, Ni, and Au gate contacts 0.7 mm in diameter were formed by ion beam sputtering
and lift-off. Energy band diagrams of the MOS capacitors were determined using the photoelectric, electric, and optical measurement
methods. Optical method (ellipsometry) was used to determine the gate and dielectric layer thicknesses and their optical indices:
the refraction n and the extinction k coefficients. Electrical method of C = f(VG) characteristic measurements allowed to determine the doping density ND and the flat band voltage VFB in the semiconductor.
Most of the parameters which were necessary for the construction of the band diagrams and for determination of the basic physical
properties of the structures (e.g. the effective contact potential difference ϕMS) were measured by several photoelectric methods and calculated using the measurement data. As a result, complete energy band
diagrams have been determined for MOS capacitors with three different gate materials and they are demonstrated for two different
gate voltages VG: for the flat-band in the semiconductor (VG = VFB) and for the flat-band in the dielectric (VG = VG0). 相似文献