Improved quality GaN by growth on compliant silicon-on-insulator substrates using metalorganic chemical vapor deposition

The use of compliant silicon-on-insulator (SOI) substrates instead of Si substrates is shown to improve the quality of epitaxial GaN layers by releasing the strain and absorbing the generated threading dislocations in the thin Si overlay of the SOI substrate. GaN layers have been grown on SOI substrates by low-pressure metalorganic chemical vapor deposition and various growth conditions and compared with GaN layers grown on Si substrates. Crystal uniformity, surface morphology, and number of threading dislocations of GaN layers grown on SOI substrates are improved compared to layers grown directly on Si substrates as evidenced by x-ray diffraction spectroscopy (XRD) and transmission electron microscopy. Full width at half maximum XRD values improved from 672 to 378 arcsec by growth on SOI instead of Si substrates. The GaN layers grown directly on Si substrates are highly resistive while all as-grown GaN layers on SOI substrates are unintentionally nn type. For a 1–2 μm thick GaN layer grown on SOI, the electron mobility is typically in the order of 102 cm2/V s102cm2/Vs with a background carrier concentration in the range of 1.5–5.0×1017 cm−3.1.5–5.0×1017cm−3. © 1998 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70972/2/JAPIAU-83-7-3829-1.pd

Photoluminescence properties of GaN grown on compliant silicon-on-insulator substrates

A compliant substrate approach has been employed to release lattice-mismatch caused strain in GaN epilayers through stress absorption in the substrate. GaN layers have been grown on silicon-on-insulator (SOI) substrates by low-pressure metalorganic chemical vapor deposition. Photoluminescence measurements at 4 K show the spectrum of grown GaN being dominated by UV emission around 3.47 eV related to neutral-donor bound excitons. The much weaker yellow luminescence shows a broad spectrum around 2.16 eV. Peak position of the UV emission changes both with measurement temperature and strain. At room temperature, the UV peak is red shifted by 64 meV corresponding well to the band-gap temperature dependence. Strain-induced blue shift of the peak, compared to unstrained GaN, is much less than for growth on sapphire, indicating strain relief in the GaN by growth on SOI. Further reduction of the blue shift is consistent with increased electron mobility. © 1997 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70808/2/APPLAB-71-26-3880-1.pd

Erratum: “Nonlinear optical response of GaN layers on sapphire: The impact of fundamental beam interference” [Appl. Phys. Lett. 76, 810 (2000)]

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70473/2/APPLAB-76-11-1479-1.pd

Impact of doping and MOCVD conditions on minority carrier lifetime of zinc- and carbon-doped InGaAs and its applications to zinc- and carbon-doped InP/InGaAs heterostructure bipolar transistors

The impact of doping and metalorganic chemical vapour deposition growth conditions on the minority carrier lifetime of zinc- and carbon-doped InGaAs is reported. Room temperature photoluminescence measurements have been employed to obtain direct information on the non-radiative lifetime of the materials. Low growth temperature and low V/III ratio lead to the lower carrier lifetime of the carbon-doped InGaAs samples. InP/InGaAs heterostructure bipolar transistors were grown and fabricated using both zinc- and carbon-doped InGaAs layers as the base regions. The current gain values measured for these devices agree well with the values calculated from the carrier lifetime and mobility/diffusion coefficient measurements.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/48935/2/s20601.pd

Myelin-associated glycoprotein gene mutation causes Pelizaeus-Merzbacher disease-like disorder

Pelizaeus-Merzbacher disease is an X-linked hypomyelinating leukodystrophy. Lossos et al. describe a family with an early-onset Pelizaeus-Merzbacher disease-like phenotype that slowly evolves into complicated hereditary spastic paraplegia, affecting both the CNS and PNS. Exome sequencing reveals a causative homozygous missense mutation in MAG, which encodes myelin associated glycoprotei

Expression of Tas1 Taste Receptors in Mammalian Spermatozoa: Functional Role of Tas1r1 in Regulating Basal Ca2+ and cAMP Concentrations in Spermatozoa

Background: During their transit through the female genital tract, sperm have to recognize and discriminate numerous chemical compounds. However, our current knowledge of the molecular identity of appropriate chemosensory receptor proteins in sperm is still rudimentary. Considering that members of the Tas1r family of taste receptors are able to discriminate between a broad diversity of hydrophilic chemosensory substances, the expression of taste receptors in mammalian spermatozoa was examined. Methodology/Principal Findings: The present manuscript documents that Tas1r1 and Tas1r3, which form the functional receptor for monosodium glutamate (umami) in taste buds on the tongue, are expressed in murine and human spermatozoa, where their localization is restricted to distinct segments of the flagellum and the acrosomal cap of the sperm head. Employing a Tas1r1-deficient mCherry reporter mouse strain, we found that Tas1r1 gene deletion resulted in spermatogenic abnormalities. In addition, a significant increase in spontaneous acrosomal reaction was observed in Tas1r1 null mutant sperm whereas acrosomal secretion triggered by isolated zona pellucida or the Ca2+ ionophore A23187 was not different from wild-type spermatozoa. Remarkably, cytosolic Ca2+ levels in freshly isolated Tas1r1-deficient sperm were significantly higher compared to wild-type cells. Moreover, a significantly higher basal cAMP concentration was detected in freshly isolated Tas1r1-deficient epididymal spermatozoa, whereas upon inhibition of phosphodiesterase or sperm capacitation, the amount of cAMP was not different between both genotypes. Conclusions/Significance: Since Ca2+ and cAMP control fundamental processes during the sequential process of fertilization, we propose that the identified taste receptors and coupled signaling cascades keep sperm in a chronically quiescent state until they arrive in the vicinity of the egg - either by constitutive receptor activity and/or by tonic receptor activation by gradients of diverse chemical compounds in different compartments of the female reproductive tract

Interface properties and electrical characteristics of III-V nitride-based MISFETS

III-V Nitride Based MISFETs have been studied using AIN/GaN heterostructures grown by MOCVD at the University of Michigan. MIS structures fabricated on such materials showed very low interface state density Dit values of -lx1011cm-2eV-1. The maximum drain current of AIN/GaN MISFETs made on these materials was greater than 700mA/mm, while drain-source breakdown was 30 V and drain-gate breakdown was 40V. Devices with a gate length of 2(j.m exhibited a peak transconductance of 136mS/mm at VGS=1V, which exceeds previously reported results