AlGaAs/GaAs photovoltaic converters for high power narrowband radiation

AlGaAs/GaAs-based laser power PV converters intended for operation with high-power (up to 100 W/cm(2)) radiation were fabricated by LPE and MOCVD techniques. Monochromatic (lambda = 809 nm) conversion efficiency up to 60% was measured at cells with back surface field and low (x = 0.2) Al concentration 'window'. Modules with a voltage of 4 V and the efficiency of 56% were designed and fabricated

High Intensity Low Temperature (HILT) performance of space concentrator GaInP/GaInAs/Ge MJ SCs

In the work, the results of an investigation of GaInP/GaInAs/Ge MJ SCs intended for converting concentrated solar radiation, when operating at low temperatures (down to -190 degrees C) are presented. A kink of the cell I-V characteristic has been observed in the region close to V-oc starting from -20 degrees C at operation under concentrated sunlight. The causes for its occurrence have been analyzed and the reasons for formation of a built-in potential barrier for majority charge carriers at the n-GaInP/n-Ge isotype hetero-interface are discussed. The effect of charge carrier transport in n-GaInP/n-p Ge heterostructures on MJ SC output characteristics at low temperatures has been studied including EL technique

Characterization of the manufacturing processes to grow triple-junction solar cells

A number of important but little-investigated problems connected with III-V/Ge heterostructure in the GaInP/GaInAs/Ge multijunction solar cells grown by MOVPE are considered in the paper. The opportunity for successfully applying the combination of reflectance and reflectance anisotropy spectroscopy in situ methods for investigating III-V structure growth on a Ge substrate has been demonstrated. Photovoltaic properties of the III-V/Ge narrow-band subcell of the triple-junction solar cells have been investigated. It has been shown that there are excess currents in the Ge photovoltaic p-n junctions, and they have the tunneling or thermotunneling character. The values of the diode parameters for these current flow mechanisms have been determined. The potential barrier at the III-V/Ge interface was determined and the origin of this barrier formation during MOVPE heterogrowth was suggested

Increasing the quantum efficiency of InAs/GaAs QD arrays for solar cells grown by MOVPE without using strain-balance technology

Research into the formation of InAs quantum dots (QDs) in GaAs using the metalorganic vapor phase epitaxy technique ispresented. This technique is deemed to be cheaper than the more often used and studied molecular beam epitaxy. The bestconditions for obtaining a high photoluminescence response, indicating a good material quality, have been found among awide range of possibilities. Solar cells with an excellent quantum ef?ciency have been obtained, with a sub-bandgapphoto-response of 0.07 mA/cm2per QD layer, the highest achieved so far with the InAs/GaAs system, proving the potentialof this technology to be able to increase the ef?ciency of lattice-matched multi-junction solar cells and contributing to abetter understanding of QD technology toward the achievement of practical intermediate-band solar cells

Experimentelle Untersuchung zur Wirkung von Druckdifferenzen in Melkzeugen mit periodischem und kontinuierlichem Lufteinlass auf Merkmale der Melkbarkeit und Zitzenbeschaffenheit

Beim maschinellen Milchentzug bei 18 Kuehen wurden die Faktoren periodischer- bzw. kontinuierlicher Lufteinsatz mit 4 verschiedenen Druckverhaeltnissen im Pulsraum waehrend der Druckphase (=Druckdifferenz) vergleichend geprueft. Die Gesamtmilchmengenleistungen und die Maschinenhauptgemelke blieben von den untersuchten Kombinationen unbeeinflusst. Mit zunehmender Druckdifferenz wurde eine Zunahme der Nachgemelke festgestellt. Kutimetermessungen an der Zitze zeigten keine chronischen Reaktionen auf die Behandlungen. Mit zunehmender Druckdifferenz wurden die Messwerte aber gleich nach dem Melken kleinerAvailable from: Hohenheim Univ., Stuttgart (Germany, F.R.). Universitaetsbibliothek / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Interferometrically enhanced sub-terahertz picosecond imaging utilizing a miniature collapsing-field-domain source

Abstract Progress in terahertz spectroscopy and imaging is mostly associated with femtosecond laser-driven systems, while solid-state sources, mainly sub-millimetre integrated circuits, are still in an early development phase. As simple and cost-efficient an emitter as a Gunn oscillator could cause a breakthrough in the field, provided its frequency limitations could be overcome. Proposed here is an application of the recently discovered collapsing field domains effect that permits sub-THz oscillations in sub-micron semiconductor layers thanks to nanometer-scale powerfully ionizing domains arising due to negative differential mobility in extreme fields. This shifts the frequency limit by an order of magnitude relative to the conventional Gunn effect. Our first miniature picosecond pulsed sources cover the 100–200 GHz band and promise milliwatts up to ∼500 GHz. Thanks to the method of interferometrically enhanced time-domain imaging proposed here and the low single-shot jitter of ∼1 ps, our simple imaging system provides sufficient time-domain imaging contrast for fresh-tissue terahertz histology

Collapsing-field-domain-based 200 GHz solid-state source

Abstract A simple miniature source generating pulse trains with a central frequency of ∼100 GHz and a duration of 50–100 ps has been demonstrated recently. The source is based on nanometer-scale collapsing field domains (CFDs) generated in the collector of an avalanching bipolar GaAs transistor. The central frequency is determined by the domain transient time across the collector, and thus, a routine increase in the oscillation frequency from 0.1 to 0.3–0.5 THz would require a reduction in the collector thickness by a factor of 3–5. This is not acceptable, however, since it would reduce the maximum blocking voltage affecting the achievable peak current across the avalanche switch. We suggest here a solution to this challenging problem by reducing the CFD travel distance while keeping the collector thickness unchanged. Here, the discovered and interpreted phenomenon of CFD collapse when entering a dense carrier plasma zone made it possible by means of bandgap engineering. A CFD emitter generating ∼200 GHz wavetrains of ∼100 ps in duration is demonstrated. This finding opens an avenue for the increase in the oscillation frequency without any reduction in the emitted power, by using a smart structure design

Light Emitting Devices Based on Quantum Well-Dots

We review epitaxial formation, basic properties, and device applications of a novel type of nanostructures of mixed (0D/2D) dimensionality that we refer to as quantum well-dots (QWDs). QWDs are formed by metalorganic vapor phase epitaxial deposition of 4–16 monolayers of InxGa1−xAs of moderate indium composition (0.3 < x < 0.5) on GaAs substrates and represent dense arrays of carrier localizing indium-rich regions inside In-depleted residual quantum wells. QWDs are intermediate in properties between 2D quantum wells and 0D quantum dots and show some advantages of both of those. In particular, they offer high optical gain/absorption coefficients as well as reduced carrier diffusion in the plane of the active region. Edge-emitting QWD lasers demonstrate low internal loss of 0.7 cm−1 and high internal quantum efficiency of 87%. as well as a reasonably high level of continuous wave (CW) power at room temperature. Due to the high optical gain and suppressed non-radiative recombination at processed sidewalls, QWDs are especially advantageous for microlasers. Thirty-one μm in diameter microdisk lasers show a high record for this type of devices output power of 18 mW. The CW lasing is observed up to 110 °C. A maximum 3-dB modulation bandwidth of 6.7 GHz is measured in the 23 μm in diameter microdisks operating uncooled without a heatsink. The open eye diagram is observed up to 12.5 Gbit/s, and error-free 10 Gbit/s data transmission at 30 °C without using an external optical amplifier, and temperature stabilization is demonstrated