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  • 1
    Electronic Resource
    Electronic Resource
    Theoretical performance of wurtzite and zincblende InGaN/GaN quantum well lasers (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 2087-2089 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The theoretical gain, radiative and Auger recombination rates, and threshold current densities of ideal wurtzite (WZ) and zincblende (ZB) 20 Å In0.2Ga0.8N/70 Å GaN multiple quantum well laser diodes are compared. We obtain upper bounds on device performance, which are based on reliable calculations for both band structure and recombination dependent features and show (1) that the performance of present devices having the ZB and WZ structures are within 20% of each other in InGaN/GaN, and (2) that present performance of the best currently available devices is only a factor of 3–4 below the theoretical limit. Radiative recombination is far more important than Auger processes. The calculations are performed using a superlattice K⋅p formalism and density functional theory within the local-density approximation. The latter yields bulk zone-center energies, wave functions, and directly calculated momentum matrix elements. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.122386
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  • 2
    Electronic Resource
    Electronic Resource
    Long wavelength InAs/InGaSb infrared detectors: Optimization of carrier lifetimes (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 7143-7152 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The performance characteristics of type-II InAs/InxGa1−xSb superlattices for long and very long-wave infrared detection are discussed. This system promises benefits in this wavelength range over conventional technology based on Hg1−xCdxTe, in part because of suppressed band-to-band Auger recombination rates which lead to improved values of detectivity. The formalism for calculating Auger rates in superlattices is developed and the physical origin of Auger suppression in these systems is discussed. Accurate K⋅p band structures are used to obtain radiative, electron–electron, hole–hole, and band-to-band Auger rules, as well as shallow trap level assisted Auger recombination rates for photodiodes. Theoretical limits for high temperature operation of ideal photovoltaic detectors are presented and compared with HgCdTe. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360422
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  • 3
    Electronic Resource
    Electronic Resource
    Reply to "Comment on ‘Temperature limits on infrared detectivities of InAs/InxGa1−xSb superlattices and bulk Hg1−xCdxTe' '' [J. Appl. Phys. 74, 4774 (1993)] (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 4156-4158 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Our calculations of the relative performance of ideal superlattice and HgCdTe (MCT) photovoltaic long wave infrared detectors, criticized in the previous Comment, do include radiative lifetimes. They also find the Auger-7 lifetime to be shorter than the radiative lifetime for p doping levels of 1017 cm−3. This agrees with other calculations and with the majority of experiments. The issue of detector thickness raised in the comment is not relevant since neither MCT nor the superlattices has an intrinsic advantage in this respect. The superlattices are further favored relative to MCT by lower tunneling currents, higher uniformity, and materials processing advantages. We suggest the superlattice system to be promising for the eventual realization of high-performance detectors. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359528
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  • 4
    Electronic Resource
    Electronic Resource
    Theoretical performance limits of 2.1–4.1 μm InAs/InGaSb, HgCdTe, and InGaAsSb lasers (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 4552-4559 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ideal threshold current densities of 2.1–4.1 μm IR lasers are calculated for active layers composed of InAs/InGaSb superlattices, InGaAsSb quantum well quaternaries, InAsSb bulk ternaries, and HgCdTe superlattices. The fully K-dependent band structure and momentum matrix elements, obtained from a superlattice K⋅p calculation, are used to calculate the limiting Auger and radiative recombination rates and the threshold current density. InGaAsSb quantum wells and InAs/InGaSb superlattices are found to be more promising laser candidates than HgCdTe superlattices and InAsSb bulk ternaries. The calculated threshold current densities of InAs/InGaSb superlattices are similar to those of InGaAsSb active layers at 2.1 μm, but are significantly lower at longer wavelengths. Comparison with experiment indicates that the threshold current densities of InGaAsSb-based devices are about three times greater than those calculated for 25 cm−1 gain. The threshold current densities of present InAs/InGaSb superlattices are about 100 times above their theoretical limit. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359798
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  • 5
    Electronic Resource
    Electronic Resource
    Multilayer thermoelectric refrigeration in Hg1−xCdxTe superlattices (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 3195-3198 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The thermoelectric figure of merit ZT of Hg1−xCdxTe superlattices (SLs) having currents along the growth axis is computed using a realistic SL band structure and the multisubband Boltzmann equation. For a narrow well and wide barrier, a heavy C1 and higher-lying light C2 subband combine to form a (nonoptimal) carrier-energy filter, enhancing the thermopower. The multilayer thermionic emission model accounts for this effect qualitatively but not quantitatively. However, for a narrow well and narrow-barrier system, ZT is 20% larger than that in the wide-barrier structure, indicating that devices based on carrier-energy filter/thermionic processes are not necessarily advantageous. ZT is almost three times larger than that in Bi2Te3 and is four times larger than that in an alloy with the average composition of the SL. This effect is associated with reduced lattice thermal conductivity in the SL rather than improved electronic transport. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371188
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  • 6
    Electronic Resource
    Electronic Resource
    Induced electric fields in anisotropic thermoelectric materials (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 5065-5069 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Transport in an anisotropic material can create potentially large induced transverse fields which reduce the measured electric and thermal conductivities relative to those computed without the induced fields. These affect the thermoelectric figure of merit ZT modestly. The induced electric field in n-type Bi2Te3 is predicted to be as much as 76% of the external one and can lower the measured electrical conductivity by up to 60%. In Hg1−xCdxTe superlattices, the anisotropy may be increased by varying the composition and width of the barrier and well to give induced fields much larger than the applied one. These effects should be easily observable. The present work utilizes general results applied to a microscopic model relevant for multivalleyed materials within the effective-mass and relaxation-time approximations. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371480
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  • 7
    Electronic Resource
    Electronic Resource
    Reply to "Comment on ‘Temperature limits on infrared detectivities of InAs/InxGa1−xSb superlattices and bulk Hg1−xCdxTe' '' [J. Appl. Phys. 80, 2542 (1996)] (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 2545-2546 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Despite the preceding Comment's assertions, the maximum theoretical detectivities of LWIR InAs/InGaSb superlattices are greater than those of HgCdTe provided the comparison involves the same base layer thicknesses (greater than the minority carrier diffusion length). The higher optimal doping of the superlattices relative to HgCdTe results in noise suppression. It is desirable because Auger recombination is substantially depressed. Shockley–Van Roosbroeck optical recombination and hence photon recycling is of little consequence in realistic device structures. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363044
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  • 8
    Electronic Resource
    Electronic Resource
    Coherent exciton lasing in ZnSe/ZnCdSe quantum wells? (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 66 (1995), S. 1313-1315 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A new mechanism for exciton lasing in ZnSe/ZnCdSe quantum wells is proposed. Lasing, occurring below the lowest exciton line, may be associated with a BCS-like condensed (coherent) exciton state. This state is most stable at low temperatures for densities in the transition region separating the exciton Bose gas and the coherent exciton state. Calculations show the gain region to lie below the exciton line and to be separated from the absorption regime by a transparency region of width, for example, about 80 meV for a 90 A(ring) ZnSe/Zn0.75Cd0.25Se quantum well. Experimental observation of the transparency region using differential spectroscopy would confirm this picture. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.113226
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  • 9
    Electronic Resource
    Electronic Resource
    Prothrombin in Normal Human Cerebrospinal Fluid Originates from the Blood (1998)
    Springer
    Neurochemical research 23 (1998), S. 1027-1030 
    Details
    ISSN: 1573-6903
    Keywords: CSF-proteins ; blood-CSF barrier ; prothrombin ; coagulation factors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract In spite of the fact that prothrombin is produced by cells within the central nervous system, its presence in the cerebrospinal fluid (CSF) has not been investigated. We determined the concentration of prothrombin in CSF with reference to the concentration in plasma in paired samples from 18 “normal” control patients and 4 patients with relapsing-remitting type of multiple sclerosis (MS). The newly developed ELISA was very specific (no cross-reactivity with thrombin) and sensitive (detection limit—0.7 ng/ml) with an imprecision of CV = 8.3% (intraseries) and 7.0% (interassay). The mean prothrombin concentration in normal CSF was 0.55 mg/l (CV ± 33%, range: 0.28–0.93 mg/l), in normal plasma 121.8 mg/l ± 21%, resulting in a mean CSF/plasma concentration quotient (QProth)—4.5 · 10−3 (CV ± 35%, range: 2.1–8.3 · 10−3) corresponding to a mean albumin quotient in this group of subjects of QAlb = 5.8 · 10−3. Due to the QProth and the molecular weight of prothrombin (72 kDa)—similar to that of albumin—we conclude that prothrombin in normal human CSF originates predominantly (〉95%) from blood. The enzymatic activity in CSF is conserved. Comparable results obtained in MS patients with only few small MRI lesions suggest that local chronic inflammatory disease of the central nervous system does not influence prothrombin concentration in the CSF if the blood-CSF barrier function is normal.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1020747716815
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  • 10
    Electronic Resource
    Electronic Resource
    Prothrombin Concentration in the Cerebrospinal Fluid Is Not Altered in Alzheimer's Disease (1999)
    Springer
    Neurochemical research 24 (1999), S. 1531-1534 
    Details
    ISSN: 1573-6903
    Keywords: Prothrombin ; ELISA ; cerebrospinal fluid ; blood-CSF barrier ; Alzheimer ; neurological disorders
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Prothrombin, known to be expressed in brain and to possess growth modulating properties, has been suggested to be involved in the pathogenesis of Alzheimer's disease (AD). We studied prothrombin concentration in lumbar CSF (L-CSF) in patients with AD (n = 25), neurologic disease controls (NDC; n = 33) covering a wide range of neurologic disorders, and subjects with Guillain-Barré syndrome (GBS; n = 4) as well as in samples of non-pathological ventricular CSF (V-CSF; n = 4). The results were evaluated with respect to CSF flow rate, as indicated by the albumin quotient (QAlb). The concentrations of prothrombin in L-CSF in NDC (mean: 0.46 mg/l, range: 0.21–0.96), and AD (mean: 0.6 mg/l, range: 0.19–1.2) were in the normal range reported previously. Expectedly, prothrombin concentration in L-CSF of GBS was increased (mean: 6.3 mg/l, range: 2.3–9.7) corresponding to the increased QAlb in this group (mean 54.6 × 10−3, range: 17–88.1). The concentrations of both prothrombin and albumin were 5.5-fold higher in L-CSF than in V-CSF (mean QAlb : 1.1 × 10−3, mean concentration of prothrombin: 0.088 mg/l). In conclusion, CSF prothrombin in all conditions evaluated here is exclusively derived from blood.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1021147914843
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