Nobuo Tsukamoto

Visible photoluminescence of Ge microcrystals embedded in SiO2 glassy matrices

Ge microcrystals embedded in SiO2 glassy matrices were formed by a radio‐frequency magnetron cosputtering technique and then annealed at 800 °C for 30 min. The average radius of the Ge microcrystals in SiO2 was determined to be about 3 nm by means of Raman spectroscopy and high resolution electron microscope. The annealed sample showed a strong room temperature luminescence with a peak at 2.18 eV. This is consistent with quantum confinement of electrons and holes.

Pragmatic trellis coding applied to rectangular QAM

Although Ungerboecks TCM (trellis coded modulation) is attractive in terms of high efficiency with low descending data rate by coding and high coding gain, it is difficult to implement. To remove this complexity, a pragmatic approach to the TCM, which is realized by employing the de facto convolutional code (constraint length K=7 and rate 1/2), was proposed. In this paper, a simpler realization of the TCM of rectangle type 2/sup N/ QAM (N is even number; /spl ges/ 4) by using the pragmatic approach is presented. We have independently shown the convolutional coding and the Viterbi decoding by the decomposition from two-dimensions into each one-dimension. By this decomposition, it is possible to apply the pragmatic approach to minimize the hardware and cost. Therefore, it is very useful for 64 QAM or 256 QAM applications such as digital video broadcasting over digital cable TV (ITU-T J.83) and fixed wireless access (IEEE 802.16) systems. It can be applied not only to single carrier QAM but also to multi-carrier QAM like OFDM.

Anisotropic strain relaxation in GaAs layers grown on Si(100) substrates by post‐growth patterning

Strain relaxation in stripe‐shaped GaAs layers on Si(100) substrates by post‐growth patterning has been investigated by photoluminescence (PL) measurements. PL spectrum for the GaAs stripes along [001] showed peaks positioned at shorter wavelength than those for stripes along [011] and [011]. The stripe‐orientation dependence was regarded as the crystallographic anisotropy of strain relaxation in the stripe‐shaped GaAs layers. The PL results, therefore, showed that the stripes along [001] were superior to those along [011] and [011] for reducing residual strain in the GaAs layers.