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Optoelectronics, IEE Proceedings -

Issue 3 • Date Jun 2000

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Displaying Results 1 - 15 of 15
  • Effects of high space-charge fields on the impulse response of the metal-semiconductor-metal photodiode

    Publication Year: 2000 , Page(s): 145 - 150
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (496 KB)  

    A two-dimensional self-consistent time-dependent simulation technique has been used to investigate electron hole transport processes in the active region of metal-semiconductor-metal photodiode structures (MSM-PD) and to analyse their high-speed response and quantum efficiency at high energy levels of the optical illumination. Different collection rates of the carriers result in space-charge fields and partial screening of the dark internal electric field. This effect gives rise to impulse response distortion and degradation of the quantum efficiency. Several ways of improving the high-speed response of the MSM-PD are analysed. The conditions for neglecting space charge effects are formulated. Modelling data are compared with experimental results on GaAs-based MSM-PD View full abstract»

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  • Modelling of InAs thin layer growth from the liquid phase

    Publication Year: 2000 , Page(s): 222 - 224
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (240 KB)  

    InAs quantum wells have been grown using the rapid slider liquid phase epitaxial growth technique. Analysis of the layer thickness data as a function of supercooling and contact time revealed the presence of two different growth mechanisms. A mathematical model of the epitaxial growth based around simple assumptions relating to melt rolling has been shown to give a good explanation of the experimental findings and also provides an integrated mathematical description of the growth phenomena View full abstract»

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  • p-GaSb/n-GaAs heterojunction diodes for TPV and solar cell applications

    Publication Year: 2000 , Page(s): 205 - 208
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (376 KB)  

    A series of samples has been grown to investigate the effect of doping and GaSb epilayer thickness on dark and photo I-V curves, and on spectral response. The optimum GaSb thickness is a trade-off between the diffusion length and the thickness required to maximise light absorption. The highest open circuit voltage, Voc~0.33 V, to date has been obtained from a thin (0.3 μm) GaSb layer doped at 6×1019 cm-1, under illumination by a focused tungsten-halogen lamp (~1 W cm-2). The short circuit current, Ioc, was ~13 mA/cm2 with a corresponding fill factor of 0.63, and an external quantum efficiency of ~10%. The devices were not anti-reflection coated, and some parameters important for solar cells, such as contact form and series resistance, have not been optimised. The shape of the spectral response is strongly dependent on GaSb thickness. Increasing the thickness of the epilayer increases the external quantum efficiency above 870 nm (i.e. above the GaAs band edge) while the external quantum efficiency in the short wavelength range (below 870 nm) reduces View full abstract»

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  • InGaAsSb photovoltaic cells with enhanced open-circuit voltage

    Publication Year: 2000 , Page(s): 199 - 204
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (468 KB)  

    Various Zn diffusion profiles in InGaAsSb photovoltaic cells with diffused emitters were experimentally studied. It was determined that strong built-in electric fields near the surface lead to a reduction of the saturation value of the injection (J01) component of the dark current, and hence to the increase of the open-circuit voltage (V oc). A value of J01 as low as 4.2×10-6 A/cm2 and a value of Voc, as high as 344 mV at 3 A/cm2 were measured View full abstract»

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  • MOVPE grown self-assembled Sb-based quantum dots assessed by means of AFM and TEM

    Publication Year: 2000 , Page(s): 209 - 215
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1200 KB)  

    Self-assembled Sb-based quantum dots (QDs) were grown by metal-organic vapour phase epitaxy and assessed by means of atomic force microscopy, transmission electron microscopy and photoluminescence. Two series of InSb QDs in a GaSb matrix were grown at 490±10°C and luminance in the mid-infrared at about 1.7 μm. Reductions in the III/V ratio and growth rate as used for the second series resulted in a change of the morphology of the InSb islands from hillocks without facets and a low level of order, to dumbbell shaped islands with distinct facets and a higher level of order. Self-assembled GaSb islands were grown on GaAs at 550°C and assessed for comparison by means of AFM View full abstract»

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  • Epitaxial growth of GaInAsSb for thermophotovoltaic devices

    Publication Year: 2000 , Page(s): 193 - 198
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (556 KB)  

    The growth and characterisation of GaInAsSb alloys, lattice-matched to GaSb substrates, are reported, with a particular focus on these alloys for thermophotovoltaic (TPV) devices. Using a unique combination of organometallic precursors, high-quality metastable GaInAsSb epitaxial layers with energy gaps as low as 0.5 eV have been grown by organometallic vapour-phase epitaxy. The GaInAsSb material quality is significantly improved for growth at a lower growth temperature of 525°C compared with 575°C, and at a higher growth rate of 5 μm/h compared with 1.2 μm/h. 4 K photoluminescence full width at half maximum values are as low as 4.3 meV for 0.59 eV GaInAsSb and 9.5 meV for 0.5 eV GaInAsSb. The importance of the surface step structure and growth kinetics on these metastable alloys is discussed. Uncoated TPV devices incorporating metastable GaInAsSb, with energy gaps in the range 0.495-0.549 eV, and a GaSb window layer exhibit an external quantum efficiency (QE) of nearly 60%, which corresponds to an internal QE of 90%. The open-circuit voltage is 313 mV for the 0.549 eV device, and decreases to 239 mV for the 0.495 eV device View full abstract»

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  • InAs/InAs(P,Sb) quantum-well laser structure for the midwavelength infrared region

    Publication Year: 2000 , Page(s): 181 - 187
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (616 KB)  

    Strained InAs1-xSbx(0<x<0.22) quantum wells with InAs, InAsP, or InAsPSb barrier layers have been grown by metal-organic vapour-phase deposition on InAs substrates. Their photoluminescence and electroluminescence were studied at 20 K. The photoluminescence peak wavelength evolution with the antimony composition x and the nature of the barrier were theoretically predicted in a satisfactory manner under the assumption of a type-II band alignment for the InAsSb/InAs system with a valence band ratio Qv =-1.30. This hypothesis leads to a type-IIa band alignment for the arsenic-rich InAsSb/InAsP system. Starting from this result, a “W” laser structure, consisting of ten periods of InAsSb/InAsP/InAsSb/InAsPSb multiquantum wells in the active region, a broadened InAsPSb waveguide, and AlAsSb cladding layers, is proposed for room-temperature emission near 3.3 μm View full abstract»

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  • Liquid crystal flow control using microfabrication techniques

    Publication Year: 2000 , Page(s): 163 - 170
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1596 KB)  

    One of the more critical parts of the fabrication of high quality liquid crystal over silicon (LCOS) devices is a controlled means of introducing the liquid crystal (LC) into the gap formed between the silicon backplane and the coverglass. Existing backplane fabrication techniques leave the mirror elements standing proud of the silicon die, causing a disruption to the LC flow-front due to capillary pinning. If the LC flow is not uniform in its spatial extent and the filling speed not tightly controlled, LC alignment defects are generated which affect the optical performance of the device in a detrimental way. To gain better control over the LC filling, a process has been developed in which the inter-mirror trenches are filled with a dielectric material. The self-aligning insulator filled trench (SIFT) process is a novel variation on the lift-off process. It has been developed to fill the inter-pixel trenches, thus producing a smooth planar surface. Different surface preparation processes are compared and it is demonstrated that this new SIFT process leads to even LC spreading, uniform LC alignment and a complete elimination of capillary pinning. The process also provides some insight into the nature of LC surface interactions View full abstract»

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  • Investigation of rare earth gettering for the fabrication of improved mid-infrared LEDs

    Publication Year: 2000 , Page(s): 217 - 221
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (440 KB)  

    The use of a rare earth gettering technique for the growth of very pure InAsSb epitaxial layers of high quantum efficiency and its application for the fabrication of powerful 4.6 μm LEDs operating at room temperature is reported. By introducing the rare earth element Gd or Yb into the liquid phase during LPE growth, it is found that the carrier concentration of InAsSb layers can be effectively reduced to ~6×1015 cm-3, and that the photoluminescence (PL) intensity of such layers can be considerably increased by between 10 and 100 times compared with untreated material. This behaviour is attributed to the gettering of residual impurities and the corresponding reduction of non-radiative recombination centres in the presence of the rare earth. This technique is used to purify the InAs0.89 Sb 0.11 ternary material in the active region of an InAs0.55Sb0.15P0.30-InAs0.89 Sb0.11 -InAs0.55Sb0.15P0.30 symmetrical double heterostructure LED. A pulsed optical output power in excess of 1 mW at room temperature is measured making these emitters suitable for use in portable instruments for the environmental monitoring of carbon monoxide at 4.6 μm View full abstract»

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  • Population inversion between subbands in simple periodical GaAs/AlAs superlattices

    Publication Year: 2000 , Page(s): 225 - 228
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (420 KB)  

    Photoluminescence (PL) from type-I GaAs-AlAs superlattices (SLs) have been studied under an electric field. In such SLs the AlAs layer, which is the barrier for the Γ subbands, is the quantum well for the X electron subbands. The X subbands in the AlAs barriers have a large density of subbands, and have a great influence on carrier transport even in type-I GaAs/AlAs SLs. Furthermore, the X subbands can be expected to be useful for carrier injection into a higher Γ subband using X-Γ resonance because PL from transitions between higher Γ subbands and hhl has been observed. Intersubband population inversion in simple periodical GaAs/AlAs SLs is presented using X-Γ resonance. Interband PL measurement and calculation of the overlap integral between electrons and hole subbands confirm the intersubband population inversion. Carrier injection into higher subbands using X-Γ resonance is expected to be useful for achieving simple quantum cascade laser structures View full abstract»

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  • Effect of intervalence band absorption on the refractive index of p-doped InSb

    Publication Year: 2000 , Page(s): 157 - 162
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (568 KB)  

    Kramers-Kronig analysis has been applied to the calculated intervalence band absorption (IVA) spectrum of p-doped InSb, calculated using 4-band Kane theory, to determine its effect on the refractive index. In the region of the band gap, IVA is found to cause a reduction in the refractive index. Other components contributing to the refractive index have also been calculated for purposes of comparison, and it is found that this reduction due to IVA is comparable to that caused by the change in the conduction-valence band absorption spectrum of p-type samples of the same doping density. It is, however, much smaller than the reductions in the refractive index caused by changes in the absorption spectrum in similarly doped n-type samples, due to the Moss-Burstein shift and free carrier absorption. The implications of these results for laser design are discussed View full abstract»

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  • Minimisation of modal birefringence in semiconductor optical guided-wave devices

    Publication Year: 2000 , Page(s): 151 - 156
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (484 KB)  

    Using a rigorous numerical approach, it is shown that the modal birefringence of semiconductor optical waveguides can be eliminated by optimising the waveguide parameters, to achieve polarisation independent performances View full abstract»

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  • Continuous wave operation of type-II interband cascade lasers

    Publication Year: 2000 , Page(s): 177 - 180
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (308 KB)  

    Continuous wave operation of interband cascade lasers based on type-II InAs/Ga(In)Sb heterostructures is reported. The interband cascade lasers, consisting of 23 cascaded active regions, lased at wavelengths near 4 μm. Continuous wave operation was observed from 60-110 μm wide by 1.02 mm long mesa-stripe lasers at temperatures up to 70 K View full abstract»

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  • Growth of antimony-based materials in a multiwafer planetary MOVPE-reactor

    Publication Year: 2000 , Page(s): 188 - 192
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (552 KB)  

    Four-junction photovoltaic solar cells are expected to reach conversion efficiencies around 40%. Mechanical stacking of two monolithic tandem cells is suggested. As a top cell the highly developed GaInP:GaAs tandem cell is considered. Device modelling is presented for the bottom cell. An infrared monolithic tandem solar cell is proposed which is a combination of an (AlGa)(AsSb) top cell (Egap=1.03 eV) and a GaSb bottom cell based on GaSb as substrate material. The MOVPE growth of GaSb, GaAsSb and AlGaSb in a multiwafer planetary reactor that is suited to large-scale industrial production is reported. Influences of the substrate preparation, orientation of the growth surface, growth temperature and the V-III ratio on material quality are presented. Both hydrogen and nitrogen were employed as the carrier gas in different experiments. The best layers were obtained on (100) substrates oriented 2° toward (111)A, using hydrogen as carrier View full abstract»

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  • Room temperature GaInAsSb/GaSb quantum well laser for tunable diode laser absorption spectroscopy around 2.35 μm

    Publication Year: 2000 , Page(s): 172 - 176
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (480 KB)  

    Novel GaInAsSb/GaSb multiple quantum well lasers grown by molecular beam epitaxy have successfully operated in continuous wave around 2.35 μm at room temperature. The temperature and current tuning properties have been characterised by tunable diode laser absorption spectroscopy. These optical properties allowed a wide spectral scan from 2.27 μm to 2.36 μm. Experiments of gas absorption have been carried out in direct absorption measurements in continuous wave regime. From the point of view of trace gas analysis, wavelength modulation has been successfully performed at 19°C around 2.36 μm. An external cavity has then been added to the setup to obtain monomodal emission. These appealing results are very attractive for portable low-cost and room temperature trace pollutants analysis View full abstract»

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