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In this study we report on manipulation of nucleation by means of periodic modulation of the growth rate, R, during molecular beam epitaxial growth of Si on Si(l11). We have found that the bilayer (BL)-by-BL growth can be improved by applying the R-modulation synchronized with the nucleation and that the phase of reflection high-energy electron diffraction (RHEED) intensity oscillations can be shifted independently of the bilayer (BL) deposition. A beating phenomenon of the RHEED oscillations was observed, which can be attributed to the superimposed effects of the R-modulation and the regular BL-by-BL growth. We have used the phenomenological correspondence between the surface step density and the RHEED oscillations as a basis to discuss the growth. By employing a kinetic solid-on-solid Monte Carlo model without vacancies and overhangs all significant experimental features could be simulated.
Ge dots embedded in Si offer the possibility of Si-based light detection at 1.3-1.55 μm. In this communication, we report a very efficient photo-detector based on a Si/SiGe heterojunction bipolar transistor structure with 10 Ge dot layers (8 ML Ge each) incorporated in the basecollector junction. The device structures were grown using low-temperature molecular beam epitaxy, and fabricated for both normal and edge incidence with no electrical contact to the base. The processed Ge-dot transistor detectors revealed a rather low dark current density, 0.01 mA/cm2 at -2 V. Photoconductivity measurements were performed at room temperature. At 1.31 μm, responsivity values of 50 mA/W at normal incidence have been directly measured at Vce = -4 V, without involving any rescaling factor due to light coupling. This value is a ∼250-fold increase compared to a reference p-i-n diode with the same dot layer structure, due to the current amplification function of the transistor. For a rib waveguide device, a very high responsivity value of about 470 mA/W (Vce = -4V) has been obtained at 1.31 μm. Measurements were also performed at 1.55 μm, and the photo-response of the waveguide phototransistor was 25 mA/W, which is again a large improvement compared with the reference waveguide photodiode (∼1 mA/W). Moreover, time-resolved photoconductivity measurements have been carried out. The results have indicated that the device frequency performance is primarily limited by the emitterbase junction capacitance.
The electroluminescence from p-i-n diode structures with Si1-yCy/Si1-xGex layers in the depletion region has been studied. Emission attributed to an overlap of the wavefunction associated with electrons confined in the Si1-yCy layer and the wavefunction associated with holes confined in the Si1-xGe, layer has been observed. For low injection currents, emission due to recombination occurring in the Si1-xGex layer is more dominant. For structures with higher C concentration, the interface related emission can persist up to higher temperatures.
Electroluminescence (EL) of Si bulk materials has been studied using lowly doped substrate with two Al-Si Schottky contacts. By applying a forward bias on the structure, the intense light emissions at 1.094 eV due to the TO-phonon assisted recombination was obtained at 40 K while other TA- and 2TO-associated transitions were also observed. The Si-TO EL peak persists up to RT with a radiative decay of ∼ 5 μs. EL emission mechanisms of these Si Schottky diodes are discussed based on temperature dependent- and injection current-dependent EL measurements.
Ninety-nine individual plants of a segregating F2 population of a wheat single cross Wen 6×CP184.108.40.206.1 were used in this study to find out whether CP220.127.116.11.1, a derivative of Triticum spelta var. album, carries a novel stripe rust resistance gene other than Yr5. Using molecular marker technology, it was found that only one out of 150 SSR primers could produce amplified polymorphism, and a marker, Xgwm155-147bp, located on chromosome 3A, was found to be linked to the stripe rust resistance gene identified with a genetic distance of 40.5 cM, indicating that the latter was also located on chromosome 3A. Since the only Yr gene previously reported to originate from T. spelta var. album is Yr5, located on 2BL, the only logical inference is that there might be other Yr gene (genes) in T. spelta, and the Yr gene identified in the present study might be a novel one. It was temporarily designated YrSp.
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