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We determined the distribution of 2 components of the extracellular matrix, fibronectin and laminin, in normal, premalignant, and malignant oral mucosa. Both indirect immunofluorescence and avidin-biotin complex immunoperoxidase techniques were used with antisera to each glycoprotein. Fibronectin was consistently present in the basement membrane and connective tissue of normal, leukoplakic and malignant oral mucosa regardless of anatomic site. A continuous laminin-reactive basement membrane structure separated tumor parenchyma from the associated stroma except in areas of invasion in which no laminin staining was evident. [ABSTRACT FROM AUTHOR]

Early-stage lesions of Kaposi's sarcoma (KS) are composed of single-layered, highly flattened cells lining collagen bundles, whereas late-stage lesions contain densely packed, spindle-shaped cells. We examined the progression of KS lesions in oral mucosa and lymph nodes from patients with AIDS, using antibodies specific for blood vascular endothelial cells (Factor VIII-related antigen) and their basement membrane (Type IV collagen and laminin). In addition, the plant lectin Ulex europaeus, which selectively stains blood vessels, was also used. In early-stage KS lesions, fibronectin, laminin and Type IV collagen were co-distributed at the interface between KS cells and collagen bundles; Factor VIII-related antigen and Ulex europaeus lectin staining was present in vascular channels and in the KS cells. However, in late-stage lesions, few if any KS cells stained with antibody to Factor VIII-associated antigen, although endothelial cells lining blood vessels were positive. Strong staining for laminin and Type IV collagen was present in a pericellular pattern throughout the nodular late-stage lesions. Since lymphatic capillary endothelium does not produce basement-membrane-specific macromolecules, these results support the conclusion that KS cells are related to blood vascular endothelium but eventually lose certain endothelium-specific markers as the cells are transformed into the spindle-shaped cell type. [ABSTRACT FROM AUTHOR]

The cross-plane and in-plane thermal conductivities of the W-active stages and InAs/AlSb superlattice optical cladding layer of an interband cascade laser (ICL) were characterized for temperatures ranging from 15 K to 324 K. The in-plane thermal conductivity of the active layer is somewhat larger than the cross-plane value at temperatures above about 30 K, while the thermal conductivity tensor becomes nearly isotropic at the lowest temperatures studied. These results will improve ICL performance simulations and guide the optimization of thermal management. [ABSTRACT FROM AUTHOR]

We report continuous-wave (cw) distributed-feedback interband cascade lasers operating in a single spectral mode (λ = 3.7-3.8 μm) at temperatures between 20 and 80 °C. The first-order gratings were realized by patterning high-index germanium layers on top of narrow ridges with relatively thin top claddings. One device generated over 27 mW of cw single-mode output at 40 °C, with a side-mode-suppression ratio >30 dB, while at 80 °C it still emitted >1 mW. At 20 °C, a second device lased in a single spectral mode with <100 mW of drive power. The tuning range was 21.5 nm with temperature and 10 nm with current. [ABSTRACT FROM AUTHOR]

A new design feature for deep-well quantum cascade (QC) lasers, in which the conduction band edge of the injector region is uptapered, results in virtual suppression of carrier leakage out of the active regions of 4.8 µm emitting devices. For heatsink temperatures in the 20–90°C range the characteristic temperature coefficients for threshold, T0, and slope efficiency, T1, reach values as high as 278 and 285 K, respectively, which are nearly twice the values for conventional QC lasers. At 20°C, the threshold current density for uncoated, 30 period, 3 mm-long devices is only ∼1.8 kA/cm2. [ABSTRACT FROM AUTHOR]

It is argued that the use of induced pluripotent stem cells for regenerative therapy may soon be ethically practicable and could sidestep the various objections pertaining to other types of stem cell (human embryonic stem cells, and stem cells obtained by altered nuclear transfer or somatic cell nuclear transfer). [ABSTRACT FROM AUTHOR]

We report a five-stage interband cascade laser that operates at λ=3.75 μm in cw mode up to a maximum temperature of 319 K. With gold electroplating, epitaxial-side-up mounting, and one facet coated for high reflectivity, a 3 mm×9.2 μm ridge emits over 10 mW of cw power at 300 K. [ABSTRACT FROM AUTHOR]

A five-stage interband cascade laser with 12 μm ridge width and Au electroplating for improved epitaxial-side-up heat sinking operates cw to a maximum temperature of 257 K, where the emission wavelength is 3.7 μm. The device emits 100 mW\facet for cw operation at 80 K, 54 mW at 200 K, and 10 mW at 250 K. The beam quality is within twice the diffraction limit for injection currents up to 14 times the lasing threshold at 120 K. [ABSTRACT FROM AUTHOR]

Carrier transport properties of AlGaN/GaN heterostructures have been analyzed with the quantitative mobility spectrum analysis (QMSA) technique. The nominally undoped Al0.08Ga0.92N/GaN sample was grown by plasma-assisted molecular beam epitaxy on a GaN/sapphire template prepared with hydride vapor phase epitaxy. Variable-magnetic-field Hall measurements were carried out in the temperature range of 5–300 K and magnetic field range of 0.01–7 T. QMSA was applied to the experimental variable-field data to extract the concentrations and mobilities associated with the high-mobility two-dimensional electron gas and the relatively low-mobility bulk electrons for the temperature range investigated. The mobilities at T=80 K are found to be 7100 and 880 cm2/V s, respectively, while the corresponding carrier densities are 7.0×1011 and 8×1014 cm-3. Any conclusions drawn from conventional Hall measurements at a single magnetic field would have been highly misleading. [ABSTRACT FROM AUTHOR]

A mid-infrared type-II ‘W’ laser fabricated by releasing the epitaxial film from its original InAs substrate is reported. The process exploits the extreme selectivity between GaSb and InAs when etched by hydrochloric acid. The detached film is coated with an Si3N4 optical cladding layer, grafted to a foreign GaAs substrate, and cleaved into laser bars. For epitaxial-side-up mounting, the device operates to 70K, with a low threshold (≅150 W=cm²) when pumped with the maximum available CW power of 320 mW from a 980 nm laser diode. [ABSTRACT FROM AUTHOR]

The effect of modulation doping by Be on the ferromagnetic properties of Ga[sub 1-x]Mn[sub x]As is investigated in Ga[sub 1-x]Mn[sub x]As/Ga[sub 1-y]Al[sub y]As heterojunctions and quantum wells. Introducing Be acceptors into the Ga[sub 1-y]Al[sub y]As barriers leads to an increase of the Curie temperature T[sub C] of Ga[sub 1-x]Mn[sub x]As, from 70 K in undoped structures to over 100 K with the modulation doping. This increase is qualitatively consistent with a multiband mean field theory simulation of carrier-mediated ferromagnetism. An important feature is that the increase of T[sub C] occurs only in those structures where the modulation doping is introduced after the deposition of the magnetic layer, but not when the Be-doped layer is grown first. This behavior is expected from the strong sensitivity of Mn interstitial formation to the value of the Fermi energy during growth. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report on the characterization of molecular-beam epitaxy-grown Ga[sub 0.75]In[sub 0.25]Sb/InAs/Al[sub 0.15]Ga[sub 0.85]As[sub 0.05]Sb[sub 0.95] “W” quantum-well light-emitting diodes (LED). The devices demonstrated room-temperature emission with a peak wavelength of 3.3 µm. A pulsed current output power of 55 µW with a slope efficiency of 98 µW/A was measured and the 300 K internal efficiency was estimated to be 2.5%. Comparative power analysis suggests that LED and laser diode efficiencies are limited by the same thermally activated nonradiative mechanism, probably Auger recombination. © 2001 American Institute of Physics. [DOI: 10.1063/1.1426267]. [ABSTRACT FROM AUTHOR]

We have observed a large increase in the magnetoresistance (MR) of molecular beam epitaxy grown Bi thin films, which were subjected to a postannealing procedure 3 °C below the Bi melting point. We have achieved an increase in the MR by a factor of 2560 at helium temperatures compared with of 343 for an as-grown film. The enhancement of the MR in the annealed films is due to higher electron and hole mobilities (μ[sub e]approx. 1×10[sup 6] cm[sup 2]/V s at 5 K) relative to those of the as-grown films (μ[sub e]approx. 9×10[sup 4] cm[sup 2]/V s at 5 K). The enhancement of the mobility in the annealed films is also supported by the observation of Shubnikov–de Haas oscillations. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report a photonic-crystal distributed-feedback (PCDFB) laser with an antimonide type-II “W” active region. Optical lithography and dry etching were used to pattern the two-dimensional rectangular lattice with a second-order grating tilted by 20° relative to the facet normal. For pulsed optical pumping, the emission line centered on λ=4.6–4.7 μm is considerably narrower (7–10 nm) than for Fabry-Pe´rot and angled-grating DFB (α-DFB) lasers fabricated from the same wafer. The PCDFB beam quality is also substantially enhanced, e.g., by a factor of 5 compared with the α-DFB at a pump-stripe width of 200 μm. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report pulsed emission from an optically pumped lead-salt vertical-cavity surface-emitting laser with a PbSe/PbSrSe quantum-well active region. The lasing wavelength of λ=4.44 μm is nearly constant over the temperature range 200-280 K, and the threshold is only 10.5 kW/cm2 at 260 K, where the gain peak and cavity mode are in resonance. Over 330 mW of peak power is emitted at 260 K, into a circular beam whose divergence angle increases with pump intensity. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

It is demonstrated that the suppression of parasitic Fabry-Perot-like lasing modes substantially enhances the beam quality and brightness of wide-stripe angled-grating distributed feedback lasers emitting in the midwave infrared. The direct facet-to-facet gain path is blocked by loss regions that are created by ion bombardment with 900 keV silicon ions. Both virtual mesa structures, in which loss regions bound both sides of the 300-μm-wide angled gain path, and spoiler structures, in which loss is induced only near the facets, decrease the etendue of the output by nearly an order of magnitude, and increase the brightness by up to a factor of 3. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We have characterized the negative luminescent properties of photovoltaic HgCdTe detector structures with a room-temperature cutoff of 4.2 μm. Using an optical modulation method to directly measure the emittance as a function of applied bias and temperature, the blackbody signal at 295 K is found to be suppressed by a factor of 5.6. The negative luminescence efficiency of 82% and the apparent blackbody temperature change of approx. -35 K are nearly independent of heatsink temperature over the range 265-305 K. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The far-field emission characteristics and spectral purity of photonic-crystal distributed-feedback (PCDFB) lasers, in which the grating is defined on a two-dimensional lattice that is tilted with respect to the facets, are analyzed using a self-consistent time-domain simulation. It is shown that both conventional DFB and angled-grating DFB devices are special cases of the PCDFB laser, which combines and enhances the best features of each. The simulations project both high beam quality and high spectral purity out to pump stripes of width >100 μm. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report resonant cavity infrared detectors with a peak wavelength of 4.54–4.58 μm that combine external quantum efficiency (EQE) exceeding 70% with spectral bandwidth 20–40 nm and ≤2% EQE at all non-resonance wavelengths between 4 and 5 μm. A 300-nm-thick absorber assures that most of the radiation propagating in the cavity produces photocurrent rather than parasitic loss. The cavity is formed by heterogeneously bonding a midwave infrared (MWIR) nBn detector chip to a GaAs/AlGaAs distributed Bragg reflector, etching away the GaSb substrate, forming mesas with diameter ≈100 μm, depositing a Ge spacer, and then depositing a single-period Ge-SiO2 top mirror. At all temperatures between 125 and 300 K, the responsivity at 150 mV bias exceeds 2.2 A/W and the EQE exceeds 61%. When the thermal background current for a realistic system scenario with f/4 optic that views a 300 K scene is derived from the observed EQE spectra, the resulting specific detectivity D* of 7.5 × 1012 cmHz½/W at 125 K operating temperature is 4.5 times higher than for a state-of-the-art broadband MWIR HgCdTe device. Simulations of the cavity performance indicate that EQE > 90% may be feasible following minimization of parasitic optical loss and maximization of the photocarrier collection efficiency. Potential applications include free space optical communication, chemical sensing, on-chip spectroscopy, and hyperspectral imaging. [ABSTRACT FROM AUTHOR]