Background doping polarity is a critical design parameter for the performance of many optoelectronic devices, including avalanche photodiodes. We have applied a technique by using capacitance–voltage ...(CV) measurements on double mesa structures with a p-i-n or n-i-p homojunction to determine the background polarity type of the unintentionally doped intrinsic region. Because CV measurements scale with the size of the mesa, they support design flexibility in producing variable-sized top and bottom mesa diameters. In this work, we grew, fabricated, and tested AlGaAsSb and AlInAsSb random alloy double mesa p-i-n structures and undertook CV measurements at 295, 150, and 77 K. It was found that the capacitance varied with the top mesa diameter for both material systems, and not the bottom mesa diameter, indicating that the unintentionally doped intrinsic region is n-type in nature.
Abstract
We report on engineering impact ionization characteristics of In
0.53
Ga
0.47
As/Al
0.48
In
0.52
As superlattice avalanche photodiodes (InGaAs/AlInAs SL APDs) on InP substrate to design and ...demonstrate an APD with low
k
-value. We design InGaAs/AlInAs SL APDs with three different SL periods (4 ML, 6 ML, and 8 ML) to achieve the same composition as Al
0.4
Ga
0.07
In
0.53
As quaternary random alloy (RA). The simulated results of an RA and the three SLs predict that the SLs have lower
k
-values than the RA because the electrons can readily reach their threshold energy for impact ionization while the holes experience the multiple valence minibands scattering. The shorter period of SL shows the lower
k
-value. To support the theoretical prediction, the designed 6 ML and 8 ML SLs are experimentally demonstrated. The 8 ML SL shows
k
-value of 0.22, which is lower than the
k
-value of the RA. The 6 ML SL exhibits even lower
k
-value than the 8 ML SL, indicating that the shorter period of the SL, the lower
k
-value as predicted. This work is a theoretical modeling and experimental demonstration of engineering avalanche characteristics in InGaAs/AlInAs SLs and would assist one to design the SLs with improved performance for various SWIR APD application.
We simulate transport for proposed low excess-noise avalanche photodiode InAlAs/InAsSb type-II superlattice materials to evaluate their impact ionization coefficients; a key metric in determining ...avalanche photodiode performance. The ensemble Monte Carlo method is utilized to develop a stochastic transport kernel suitable for superlattice transport in the static field approximation. The electronic band structure and impact ionization rates are computed from a 14-band superlattice envelope function
K
·
p
formalism. We reveal that band engineering through superlattice design can be utilized to enhance the electron-to-hole impact ionization ratio in the InAlAs/InAsSb superlattice material system.
Colostrum intake is one of the most important factors in neonatal health in ruminants, mainly because of its unique immunological properties. Both in practice as well as in research, the attention of ...lactogenic immunity is focused on the importance of colostral antibodies and less attention is given to the functional role of maternal cells in colostrum. Here we study the transfer of maternal leukocytes via colostrum and the functionality in goat kids. In experiment 1, twenty twin pairs of goat kids from dams previously immunized with an inactivated Mycobacterium avium subsp. paratuberculosis (MAP) vaccine were fed maternal colostrum from their dam (kid 1) or pasteurized and frozen/thawed bovine colostrum (kid 2). The presence of cell mediated immune response (CMIR) against Mycobacterium avium antigens in the kids was assessed using intradermal skin testing with PPD-A tuberculin. Linear mixed effect models showed an increase in skin thickness in response to intradermal PPD-A injection in maternal colostrum fed kids compared to bovine colostrum fed kids. After intradermal PPD-A application, serum concentration of MAP specific antibodies increased in kids fed maternal colostrum, indicating antigen specific activation of the adaptive immune system. We did not detect a similar increase in antibodies in the kids fed bovine colostrum.
In experiment 2, a more reductionistic approach was applied to specifically study the effects of the transfer of maternal colostral leukocytes on CMIR in goat kids. Similar to experiment 1, twin kids from MAP immunized dams were randomly divided over two groups. The experimental group received colostrum replacer supplemented with fluorescently labelled colostral cells of the dam and the control group received colostrum replacer only. No difference in skin response following intradermal PPD-A injection was observed between both groups of kids. Histologic examination of the skin at the intradermal injection site did not show fluorescently labelled cells.
In conclusion, in our initial experiment we observed an antigen specific CMIR in goat kids fed fresh colostrum with colostral leukocytes from vaccinated dams. The lack of a DTH response in kids fed colostrum replacer supplemented with maternal colostrum derived leukocytes indicated that the complete colostral matrix is probably required for colostrum leukocytes to transfer across the intestinal epithelial barrier and modulate the neonatal immune response. In line with earlier studies, our results indicate that caprine maternal leukocytes present in colostrum can functionally contribute to the newborns’ early adaptive immune responses adding to the importance of colostrum feeding in ruminant neonates.
The interface of ZnTe/Si(211) grown by molecular beam epitaxy was investigated by high-resolution transmission electron microscopy. Several types of defects such as misfit dislocations, stacking ...faults, agglomerations of vacancies, and precipitates were observed and studied by electron microscopy at the ZnTe/Si interface. The distribution of misfit dislocations at the interface was revealed with the assistance of the fast Fourier transformation filtering technique. A stick-and-ball interface model including misfit dislocation geometry is proposed. The possible origins of the stacking faults, vacancies, and precipitates are discussed.
Strained HgTe/CdZnTe or InAs/GaInSb, and essentially unstrained HgTe/CdTe superlattices (SLs), are possible materials systems for implementation in future-generation infrared imaging systems. In ...addition to cutoff wavelengths spanning the infrared spectrum, they offer degrees of freedom in their design (e.g., layer thicknesses, alloy compositions, and number of layers in one superlattice period) that permit the optimization of an infrared detector’s figures of merit such as detectivity through the tuning of material properties such as recombination lifetimes and optical absorption. This paper provides a brief overview of the anticipated advantages of the SLs over HgCdTe alloy-based infrared photon detector technology and the relative merits of the II–VI and III–V semiconductor-based SLs.
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