Four tunnel junction (TJ) designs for multijunction (MJ) solar cells under high concentration are studied to determine the peak tunnelling current and resistance change as a function of the doping concentration. These four TJ designs are: AlGaAs/AlGaAs, GaAs/GaAs, AlGaAs/InGaP and AlGaAs/GaAs. Time‐dependent and time‐average methods are used to experimentally characterize the entire current–voltage profile of TJ mesa structures. Experimentally calibrated numerical models are used to determine the minimum doping concentration required for each TJ design to operate within a MJ solar cell up to 2000‐suns concentration. The AlGaAs/GaAs TJ design is found to require the least doping concentration to reach a resistance of <10−4 Ω cm2 followed by the GaAs/GaAs TJ and finally the AlGaAs/AlGaAs TJ. The AlGaAs/InGaP TJ is only able to obtain resistances of ≥5 × 10−4 Ω cm2 within the range of doping concentrations studied. Copyright © 2010 John Wiley & Sons, Ltd.

One of the often reported artefacts during cell preparation to scanning electron microscopy (SEM) is the shrinkage of cellular objects, that mostly occurs at a certain time-dependent stage of cell drying. Various methods of drying for SEM, such as critical point drying, freeze-drying, as well as hexamethyldisilazane (HMDS)-drying, were usually used. The latter becomes popular since it is a low cost and fast method. However, the correlation of drying duration and real shrinkage of objects was not investigated yet. In this paper, cell shrinkage at each stage of preparation for SEM was studied. We introduce a shrinkage coefficient using correlative light microscopy (LM) and SEM of the same human mesenchymal stem cells (hMSCs). The influence of HMDS-drying duration on the cell shrinkage is shown: the longer drying duration, the more shrinkage is observed. Furthermore, it was demonstrated that cell shrinkage is inversely proportional to cultivation time: the longer cultivation time, the more cell spreading area and the less cell shrinkage. Our results can be applicable for an exact SEM quantification of cell size and determination of cell spreading area in engineering of artificial cellular environments using biomaterials. SCANNING 38:625-633, 2016. © 2016 Wiley Periodicals, Inc.

Epitaxial layers of InGaAs on InP are the building blocks in optoelectronic device fabrication, where the dependence of the band gap on composition is utilized in device design. The band gap can be determined from the photoluminescence peak energy and composition from lattice size. This work reports a detailed correlation between both the room-temperature (300 K), and low-temperature (7 K) photoluminescence peak energy of epitaxial InGaAs, and the lattice mismatch relative to InP as measured by x-ray double-crystal diffraction. Nominally undoped 1- and 2-μm-thick layers of high quality InGaAs were grown on InP (001) by metalorganic chemical vapor deposition. The relaxed mismatch for these coherent layers was between −0.18% and 0.12%. The observed dependence of the 7-K photoluminescence energy on lattice mismatch confirms the theory of People [Appl. Phys. Lett. 50, 1604 (1987); Phys. Rev. B 32, 1405 (1985)] and Kuo et al. [J. Appl. Phys. 57, 5428 (1985)] which includes the effect of strain on the J= (3)/(2) valence band. The 7 K photoluminescence energy of zero mismatch InGaAs grown on semi-insulating InP substrates ([Fe]=1016 cm−3) was 0.804±0.002 eV and of zero mismatch InGaAs grown on n-type ([S]=2×1019 cm−3) substrates was 0.801±0.002 eV. This difference is attributed to the difference in absolute lattice constant for the two types of substrates. The correlation was extended to room-temperature photo- luminescence where the peak recombination energy depends on the excitation conditions. Simple spectral line-shape analysis showed that the λ 1/2  max (taken from the low-energy side of the peak) was a reliable figure of merit and could be used to estimate the degree of lattice mismatch independent of excitation conditions. This algorithm is applied to the nondestructive mapping of whole wafers.

A novel planar separate absorption, charge sheet, grading and multiplication avalanche photodiode (APD) structure incorporating a partial charge sheet in the device periphery is described, which allows for straightforward fabrication of APD devices without the use of guard rings. Metalorganic chemical vapor deposition grown, Zn-diffused InP/InGaAs APD devices have been fabricated. High dc gains well in excess of 100 and a low primary dark current of 0.1 nA at 0.99 of the breakdown voltage VB have been measured for a 40-μm-diam device. The receiver sensitivity for a bit error rate of 10−9 at a bit rate of 400 Mbit/s was −41 dBm. The −3 dB electrical bandwidth was 2.5 GHz, and the gain-bandwidth product was 30 GHz.

teristics and, especially, changes in lasing characteristics for laser diode. The effect of parameters influencing on the lasing characteristics and reliability of the laser diode are discussed previously in Refs. 7 and 8. CONCLUSIONSWe fabricated loss-coupled 1.55 m DFB laser diode having an automatically buried absorptive InAsP layer and performed the reliability test for it. The use of the automatically buried InAsP layer achieved by a single step growth makes the device fabrication process step simpler than that of conventional loss-coupled DFB LDs. High reliability was achieved for the LD, in which operating at high temperature under constant output power for 2800 h without serious device degradation and the expected meantime-to-failure was more than 10 6 h. In this article a conformal slotted array is designed in millimeter band. The work frequency band is 36.7-37 GHz. Omnidirectional azimuth radiation pattern has been achieved, as well as, a Ϫ10°to ϩ30°over the horizon elevation coverage. A short-circuit ended circular waveguide has been used to feed the slot array. Only one mode has been excited to generate the desired circular polarization (TM 01 ). Furthermore, the generated vertical currents over the waveguide walls feed each single element of the array: a pair of noncrossed slots with a separation of g /4 ( g is the waveguide wavelength in the propagated mode). The elevation radiation pattern is achieved by properly placing the slot array in the circular waveguide, which is also the surrounding ground plane of the slot array. The manufacturing antenna process is simple, precise, and lightweight. ANTENNA STRUCTUREAs Figure 1 shows the antenna is composed by eight slot pairs placed on the walls of a circular waveguide. The waveguide is finished with an inner short-circuit at a distance of d s ϭ g /4 from the centre of each slot pair. The waveguide inner diameter D g is 10 mm, so the separation between slot pairs is 0.49 0 at 36.85 GHz ( 0 is the free space wavelength). The slot array is used to generate the omnidirectional radiation pattern with low ripple in azimuth plane. The external surface from the short-circuit to the end of the circular waveguide (h s Ϸ 0 /8), can be used to slightly configure the elevation radiation pattern in the upper angles.The circular waveguide is excited in the TM 01 mode. Fundamental TE 11 and the lower losses TE 01 modes are cancelled by the modified coaxial to waveguide transition in the bottom of Figure 1 scheme. This transition is implemented by the inner conductor of a coaxial cable and an annular disc discontinuity over the inner face of the waveguide wall. By optimizing the height of the discontinuity (h d ϭ 0. A circular waveguide prototype has been manufactured to verify the return losses response of the TM 01 coaxial to waveguide transition [ Fig. 2(b)]. As measurement result in Figure 3 shows, the transition is optimized in 36.85 GHz. A below Ϫ20 dB response is obtained in the edge points of the band. SINGLE ELEMENT-SLOT PAIR AND CIRCULAR POLARIZATIONA Ϫ6 dB a...