Materials for Seebeck effect gas detectors

SIGLEAvailable from British Library Document Supply Centre- DSC:D86008 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Incorporation of silicon in -311-A and -111-A GaAs grown by molecular beam epitaxy.

The incorporation of silicon into GaAs grown by molecular beam epitaxy on Ga-terminated (311)A and (111)A surfaces has been investigated by local vibrational mode (LVM) Raman and absorption spectroscopy as well as by photoluminescence measurements. Both n- and p-type GaAs:Si layers grown on (311)A substrates show intense band edge luminescence and n-type samples also show very weak deep level emission due to SisubGa-VsubGa defect complexes. The low-temperature Raman spectrum of n-type (311)A GaAs:Si shows the LVM of high28 SisubGa donors and of compensating high28 SisubAs acceptors as peaks at the expected frequencies of 384 and 399 cmhigh-1, respectively. However, in p-type (311)A and (111)A layers only one silicon related LVM appears at 395 cmhigh-1. Similarly, in FTIR absorption a Fano profile is resolved at this frequency. The incorporation of silicon into GaAs grown by molecular beam epitaxy on Ga-terminated (311)A and (111)A surfaces has been investigated by local vibrational mod e (LVM) Raman and absorption spectroscopy as well as by photoluminescence measurements. Both n- and p-type GaAs:Si layers grown on (311)A substrates show intense band edge luminescence and n-type samples also show very weak deep level emission due to SisubGa-VsubGa defect complexes. The low-temperature Raman spectrum of n-type (311)A GaAs:Si shows the LVM of high28 SisubGa donors and of compensating high28 SisubAs acceptors as peaks at the expected frequencies of 384 and 399 cmhigh-1, respectively. However, in p-type (311)A and (111)A layers only one silicon related LVM appears at 395 cmhigh-1. Similarly, in FTIR absorption a Fano profile is resolved at this frequency

Nano-pathways: Bridging the divide between water-processable nanoparticulate and bulk heterojunction organic photovoltaics

Here we report the application of a conjugated copolymer based on thiophene and quinoxaline units, namely poly[2,3-bis-(3-octyloxyphenyl)quinoxaline-5,8-diyl-alt-thiophene-2,5-diyl] (TQ1), to nanoparticle organic photovoltaics (NP-OPVs). TQ1 exhibits more desirable material properties for NP-OPV fabrication and operation, particularly a high glass transition temperature (Tg) and amorphous nature, compared to the commonly applied semicrystalline polymer poly(3-hexylthiophene) (P3HT). This study reports the optimisation of TQ1:PC71BM (phenyl C71 butyric acid methyl ester) NP-OPV device performance by the application of mild thermal annealing treatments in the range of the Tg (sub-Tg and post-Tg), both in the active layer drying stage and post-cathode deposition annealing stage of device fabrication, and an in-depth study of the effect of these treatments on nanoparticle film morphology. In addition, we report a type of morphological evolution in nanoparticle films for OPV active layers that has not previously been observed, that of PC71BM nano-pathway formation between dispersed PC71BM-rich nanoparticle cores, which have the benefit of making the bulk film more conducive to charge percolation and extraction

A local vibrational mode investigation of p-type Si-doped GaAs

Infrared absorption (IR) and Raman scattering measurements have been made of the localized vibration modes (LVM) due to defects incorporating silicon impurities in p-type Si-doped GaAs grown by liquid phase epitaxy (LPE) on (001) planes and by molecular beam epitaxy (MBE) on (111)A and (311)A planes. Analysis of a closely compensated LPE sample indicated that an existing calibration factor for the Si subAs LVM (399 cm high-1) relating the integrated absorption coefficient (IA) to the concentration (Si subAs) should be increased by 40 %, so that IA = 1 cm high-2 corresponds to (Si subAs) = 7 x 10 high16 cm high-3. The Si subAs LVM appeared as a Fano dip in the hole absorption continuum at about 395 cm high-1 in the highly doped p-type material, some 4 cm high-1 lower in frequency than its normal position in compensated GaAs. Electron irradiation of samples led to the progressive removal of the Fano dip and a shift with the emergence of the expected Si subAs LVM absorption line at 399 cm high-1. In MBE samples the irradiation also generated Si subGa donors, but the site switching was not detected in LPE material. By contrast, Raman spectra of as-grown p.type samples exhibited a symmetrical peak at 395 cm high-1, which also shifted towards 399 cm high-1 as the free carriers were removed. MBE (111)A GaAs:Si compensated by Sn subGa donors revealed the Si subAs LVM at its normal position. After hydrogenation of MBE and LPE samples, only stretch modes due to H-Si subAs were observed. Passivated MBE GaAs (111)A codoped with Si and Be showed stretch modes due to both shallow acceptors. It was thereby concluded that only one type of acceptor (Si subAs) was present in p-type Si-doped GaAs, contrary to previous proposals. There was no evidence for the presence of Si subAs pairs or larger clusters

Extremely low threshold current density InGaAs/GaAs/AlGaAs strained SQW laser grown by MBE with As2

In this report, we present data on an InGaAs/GaAs strained single quantum well laser with the lowest reported threshold current density to date, namely 44\u2002A\u2002cm 122 for a 3\u2002mm cavity length. This was grown by solid-source molecular-beam epitaxy with the arsenic dimer, As2. The structure is that of a graded-index, separate-confinement heterostructure with a single strained InGaAs quantum well, sandwiched between GaAs barrier layers and AlGaAs cladding layers. The wavelength of the lasers was around 985\u2002nm, and the internal efficiency and losses were 69% and 0.70\u2002cm 121, respectively. In addition, data on the uniformity of our lasers, which are grown on rotating 2 in substrates (1 in\u2002=\u20022.54\u2002cm), show drops in photoluminescence emission wavelength and layer thickness of less than 4\u2002nm and 4%, respectively, from the centre to the edge of the wafer and very little compositional change.Peer reviewed: YesNRC publication: Ye