Photonik - Material und Technologien. Teilvorhaben: Integration photonischer Bauelementstrukturen mittels MOMBE Abschlussbericht

Growth of GaInAsP device structures by MOMBE had to be optimized, especially for selective area epitaxy to realize monolithic device integration. In addition the potential of MOMBE for device production had to be explored. Laser structures with strained multiple quantum well layers (MQWs) had to be fabricated and compared to MOVPE structures in terms of device performance. Laser-waveguide integration and planar-selective laser structures had to be formed by selective area epitaxy. A wafer holder for homogeneous growth in single and multi wafer (3 x 2'') operation had to be developed. A variety of MQW laser structures were fabricated with GaInAsP and InAsP layers as well material, where a compressive strain up to 2% was achieved. The MOMBE laser results are comparable to best MOVPE data. High quality waveguide-laser couplings were accomplished by embedded selective area epitaxy of the waveguide structure. Furthermore selective growth of laser structures was investigated. The threshold current densities of these lasers are comparable to data from large area reference lasers. A novel indium free wafer holder was realized resulting in excellent layer homogeneity. For GaInAsP NQW structures a standard deviation of photoluminescence #DELTA##lambda#<2 nm was obtained across more than 90% of the wafer area in multi-wafer operation for each wafer, the wafer-to-wafer standard deviation was #DELTA##lambda#<4 nm. Hence a basis for industrial use of MOMBE has been established. The investigations were performed in close cooperation with the University of Ulm, a project partner. An internationally leading position has been reached by this project. An extension of these studies to laser-modulator integration is planned for the future. (orig.)SIGLEAvailable from TIB Hannover: DtF QN1(70,42) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany)DEGerman

A unique case of reversion to normal size of a maternal premutation FMR1 allele in a normal boy

Fragile X syndrome (FXS) is caused mostly by expansion and subsequent methylation of the CGG repeat in the 5'UTR of the FMR1 gene, resulting in silencing of the gene, absence of FMRP and development of the FXS phenotype. The expansion also predisposes the CGG repeat and the flanking regions to further instability that may lead to mosaics between a full mutation and a premutation or, rarely, a normal or deleted allele. Here, we report on a 10-year-old boy with no FXS phenotype, who has a normal CGG tract, although he inherited the maternal expanded allele that causes FXS in his two brothers. Southern blotting demonstrated that the mother carries a premutation allele ( approximately 190 CGG), whereas the propositus shows a normal 5.2 kb fragment after HindIII digestion and a smaller 2.2 kb fragment after double HindIII-EagI digestion, without any apparent mosaicism in peripheral blood leukocytes. PCR and sequence analysis of the FMR1 5'UTR revealed an allele of 43 repeats, with two interspersed AGG triplets in position 10 and 25 and an exceptional CCG triplet in position 17. This latter creates an abnormal EagI site compatible with the smaller 2.2 kb fragment observed with Southern blotting. Haplotype analysis proved that the rearranged allele originated from the maternal expanded allele. To the best of our knowledge, this is the first non-mosaic case of reduction in the CGG tract of the FMR1 gene, resulting in a normal allele