The Effect of Planting Density and Supports on the Seed Yield of Mucuna cochinchinensis

Mucuna cochinchinensis was planted for seed production using six planting systems. These comprised combinations of two planting distances; 1. 0 m x 1.0 m and 2.0 m x 2.0 m with three types of supports; no support, individual pole support for each plant or the wire-trellis type of support. Plants using either type of support outyielded the seed production from plants which received no support. Mean yield of normal seeds for unsupported plants, plants with individual support and plants with the wire trellis type of support were 76,677 and 736 kg/ha respectively. The lower yield of normal seeds from unsupported plants resulted from a combination of a lower total seed yield and a higher percentage of rotten seeds. Rotten seeds in unsupported plants comprised 68 percent of total seed yield compared to 38 percent and 33 percent for individually supported and wire-trellis supported plants respectively. Differences between the two types of supports were not significant. Planting distance did not have a significant effect on seed yield. However, for plants without any support there was a higher percentage of ;otten seeds (78%) for the more closely spaced plants than for plants planted at the wider spacing (54%)

Electrical isolation of n-type and p-type InP layers by proton bombardment

The evolution of the sheet resistance(Rs) of n-type and p-type conductive InP layers during proton irradiation and the stability of the formed isolation during postirradiation annealing were investigated. It was found that the threshold dose (Dth) to convert the conductive layer to a highly resistive one is different for n- and p-type samples with similar initial free carrier concentrations. From our results, one infers that the antisite defects and/or related defect complexes formed by the replacement collisions are the carrier trapping centers, where InP is responsible for electron trapping and PIn for the hole trapping. A time dependence of the Rs was observed after each irradiation step to doses of ≅Dth and higher. This time variation is related to metastable processes involving free carriers. The thermal stability of the isolation of n-type samples is limited to temperatures lower than 200 °C, irrespectively of the irradiated dose. For p-type samples the thermal stability of electrical isolation is extended to 450–500 °C.This work was partly supported by Conselho Nacional de Pesquisas (CNPq, Brazil) under Contract No. 200541/ 99-4

A study of quantum well solar cell structures with bound-to-continuum transitions for reduced carrier recombination

A bound-to-continuum quantum well solar cell structure is proposed, and the band structure and absorption spectra are analyzed by the use of an eight band k⋅p model. The structure is based on quantum wells that only support bound states for the valence band. The absence of bound conduction band states has a number of potential advantages, including a reduction of electron trapping and, therefore, a reduction of quantum well induced photocarrier recombination due to reduced spatial overlap of the electron and hole wavefunctions.Thanks are due to the Australian Research Council for the financial support of this research

Structural characteristics of GaSb∕GaAs nanowire heterostructures grown by metal-organic chemical vapor deposition

Highly lattice mismatched (7.8%) GaAs∕GaSbnanowireheterostructures were grown by metal-organic chemical vapor deposition and their detailed structural characteristics were determined by electron microscopy. The facts that (i) no defects have been found in GaSb and its interfaces with GaAs and (ii) the lattice mismatch between GaSb∕GaAs was fully relaxed suggest that the growth of GaSbnanowires is purely governed by the thermodynamics. The authors believe that the low growth rate of GaSbnanowires leads to the equilibrium growth

Strain relaxation and phonon confinement in self-assembled InAsSb/InP (001) quantum dashes: Effect of deposition thickness and composition

This paper presents a study on the strain relaxation and phonon confinement effect in InAsSb/InP quantum dashes QDashes. The phonon mode with a frequency between that of InAs-like longitudinal optical mode and that of InP transverse optical mode is determined to be originated from InAsSb QDashes. Despite the small height of the QDashes, their phonon frequency is found to be mainly determined by the strain relaxation in the dashes. With increasing InAsSb deposition thickness and Sb composition in InAsSb dashes, the phonon mode shows an upward shift of its frequency due to the increased compressive strain.Financial support from Australian Research Council DP0774366 is gratefully acknowledged

Direct imaging of the spatial diffusion of excitons in single semiconductor nanowires

We use spatially and temporally resolved photoluminescence to measure excitondiffusion in single zinc blende GaAs/AlGaAs core/shell and mixed phase InPnanowires.Excitons in the single phase GaAs/AlGaAs nanowires are seen to diffuse rapidly throughout the nanowire with a measured diffusion constant ranging from 45 to 100 cm²/s, while in the mixed phase, InPnanowireelectrons and holes are seen to rapidly localize to the quantum confined states in the zinc blende and wurtzite segments, respectively. The diffusion constant in the GaAs/AlGaAs nanowire is similar to the best hole mobilities observed in modulation doped heterostructures.We acknowledge the financial support of the National Science Foundation through grants DMR-0806700, 0806572, 1105362, 1105121, and ECCS-1100489, and the Australian Research Council