References of "Marso, Michel 50002313"
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See detailAcoustic charge transport in GaN nanowires
Ebbecke, J.; Maisch, S.; Wixforth, A. et al

in Nanotechnology (2008), 19(27), 275708-5

We present acoustic charge transport in GaN nanowires (GaN NWs). The GaN NWs were grown by molecular beam epitaxy (MBE) on silicon(111) substrates. The nanowires were removed from the silicon substrate ... [more ▼]

We present acoustic charge transport in GaN nanowires (GaN NWs). The GaN NWs were grown by molecular beam epitaxy (MBE) on silicon(111) substrates. The nanowires were removed from the silicon substrate, aligned using surface acoustic waves (SAWs) on the piezoelectric substrate LiNbO3 and finally contacted by electron beam lithography. Then, a SAW was used to create an acoustoelectric current in the GaN NWs which was detected as a function of radio-frequency (RF) wave frequency and its power. The presented method and our experimental findings open up a route towards new acoustic charge transport nanostructuredevices in a wide bandgap material such as GaN. [less ▲]

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See detailTemperature-dependence of the phase-coherence length in InN nanowires
Blömers, Ch UL; Schäpers, Th; Richter, T. UL et al

in Applied Physics Letters (2008), 92(13), 132101-132103

We report on low-temperature magnetotransport measurements on InN nanowires, grown by plasma-assisted molecular beam epitaxy. The characteristic fluctuation pattern observed in the conductance was ... [more ▼]

We report on low-temperature magnetotransport measurements on InN nanowires, grown by plasma-assisted molecular beam epitaxy. The characteristic fluctuation pattern observed in the conductance was employed to obtain information on phase-coherent transport. By analyzing the root mean square and the correlation field of the conductance fluctuations at various temperatures, the phase-coherence length was determined. [less ▲]

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See detailCharacterization of AlGaN/GaN MOSHFETs with Al2O3 as Gate Oxide,
Gregušová, D.; Stoklas, R.; Čičo, K. et al

in Physica Status Solidi C. Current Topics in Solid State Physics (2007), 4 (2007)

We report on AlGaN/GaN metal-oxide-semiconductor heterostructure field-effect transistors (MOSHFETs) with MOCVD deposited Al2O3 as a gate oxide. Properties of MOSHFETs with 9 nm and 14 nm thick Al2O3 are ... [more ▼]

We report on AlGaN/GaN metal-oxide-semiconductor heterostructure field-effect transistors (MOSHFETs) with MOCVD deposited Al2O3 as a gate oxide. Properties of MOSHFETs with 9 nm and 14 nm thick Al2O3 are compared with conventional HFETs prepared simultaneously on the same layer structure. Lower gate leakage current (~10−5 A/mm at −10 V) and higher saturated drain current (up to 40%) are obtained for MOSHFETs than those for HFETs. In contradiction to previously reported data, the extrinsic transconductance for MOSHFETs is also higher (up to 37% of peak values) than that for HFET. This indicates on semi-conductive rather than insulating properties of Al2O3 gate oxide. Pulsed I−V measurements (pulse width 1 μs) yielded lower but still measurable current collapse in MOSHFETs compared to HFETs. Nevertheless, obtained results show that Al2O3 gate oxide, after optimising its microstructure and thickness, can be preferable for the preparation of AlGaN/GaN MOSHFETs. [less ▲]

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See detailPerformance optimization of GaAs-based photomixers as sources of THz radiation
Kordoš, P.; Marso, Michel UL; Mikulics, M.

in Applied Physics A : Materials Science & Processing (2007), 87(3), 563-567

The performance optimization of GaAs-based photomixers using novel device structures is reported. Lowtemperature grown (LT) GaAs devices with recessed interdigitated finger contacts, which improve the ... [more ▼]

The performance optimization of GaAs-based photomixers using novel device structures is reported. Lowtemperature grown (LT) GaAs devices with recessed interdigitated finger contacts, which improve the electric field distribution in the active region, were investigated. Further, the devices with an enhancedmixing area using finger contacts integrated into the coplanar stripline were experimentally verified. The output power of such photomixers was twice of that with conventional surface contacts. High-energy nitrogen implanted GaAs was used as an alternative to LT GaAs, and a further increase of the output power was observed.Measured power level of 2.6 μW at 850 GHz was higher than that reported before for any photomixer in the THz region. [less ▲]

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See detailGaN and InN nanowires grown by MBE: A comparison
Calarco, Raffaella; Marso, Michel UL

in Applied Physics A : Materials Science & Processing (2007)

Morphological, optical and transport properties of GaN and InN nanowires grown by molecular beam epitaxy (MBE) have been studied. The differences between the two materials in respect to growth parameters ... [more ▼]

Morphological, optical and transport properties of GaN and InN nanowires grown by molecular beam epitaxy (MBE) have been studied. The differences between the two materials in respect to growth parameters and optimization procedure was stressed. The nanowires crystalline quality has been investigated by means of their optical properties. A comparison of the transport characteristics was given. For each material a band schema was shown, which takes into account transport and optical features and is based on Fermi level pinning at the surface. [less ▲]

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See detailNew approaches for growth control of GaN-based HEMT structure
Hardtdegen, H.; Steins, R.; Kaluza, N. et al

in Applied Physics A : Materials Science & Processing (2007), 87(3), 491-498

This paper reports on new approaches for growth control of GaN-based heterostructures for high frequency and high power application. First in situ methods are presented and their further development ... [more ▼]

This paper reports on new approaches for growth control of GaN-based heterostructures for high frequency and high power application. First in situ methods are presented and their further development discussed [1]. The development leads to a greatly improved observation of growth parameter influences in the MOVPE of GaN. A new growth process is introduced which enhances growth reproducibility [2]. This new growth process is then optimized with respect to the envisaged application. To this end process modeling will be employed. The application envisaged is the AlxGa1−xN/GaNhigh electron mobility transistor (HEMT). At last device results will be presented. All in all it will be shown how fundamental research can drive technology and how basic knowledge can be employed forprocess development with respect to device applications. [less ▲]

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See detailTerahertz photonic mixers as local oscillators for hot electron bolometer and superconductor-insulator-superconductor astronomical receivers, ,
Cámara Mayorga, I.; Muñoz Pradas, P.; Michael, E. A. et al

in Journal of Applied Physics (2006), 100

A pump experiment of two astronomical heterodyne receivers, a superconductorinsulator- superconductor SIS receiver at 450 GHz and a hot-electron-bolometer HEB receiver at 750 GHz, is reported. A low ... [more ▼]

A pump experiment of two astronomical heterodyne receivers, a superconductorinsulator- superconductor SIS receiver at 450 GHz and a hot-electron-bolometer HEB receiver at 750 GHz, is reported. A low-temperature-grown GaAs metal-semiconductor-metal photonic local oscillator LO was illuminated by two near infrared semiconductor lasers, generating a beat frequency in the submillimeter range. I-V junction characteristics for different LO pump power levels demonstrate that the power delivered by the photomixer is sufficient to pump a SIS and a HEB mixer. SIS receiver noise temperatures were compared using a conventional solid-state LO anda photonic LO. In both cases, the best receiver noise temperature was identical Tsys=170 K . [less ▲]

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See detailOrigin of Improved RF Performance of AlGaN/GaN MOSHFETs Compared to HFETs,
Marso, Michel UL; Heidelberger, Gero; Indlekofer, Klaus Michael et al

in IEEE Transactions on Electron Devices (2006), 53(7), 1517-1723

In this paper, the influence of a 10-nm-thick silicondioxide layer, as a passivation or as a gate insulation, on the performance of heterojunction field-effect transistors (HFETs) and ... [more ▼]

In this paper, the influence of a 10-nm-thick silicondioxide layer, as a passivation or as a gate insulation, on the performance of heterojunction field-effect transistors (HFETs) and metal–oxide–semiconductor HFETs (MOSHFETs), based on an undoped AlGaN/GaN heterostructure on a SiC substrate, was investigated. Channel-conductivity results yield a nearly 50% increase of mobility in the MOSHFET samples compared to the unpassivated HFETs. This increase of the transport properties of the MOSHFET channel is confirmed by a similar 45% increase of the cutoff frequency, from 16.5 to 24 GHz. Hall measurements, however, show a 10% decrease of the mobility in the heterostructure with a SiO2 top layer. In this paper, the superior performance of the MOSHFET transistor, in contradiction to the Hall results, is attributed to the screening of the Coulomb scattering of the charged surface defects by the gate-metallization layer. [less ▲]

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See detailGaN-nanowhiskers: MBE-growth conditions and optical properties
Meijers, R.; Richter, T.; Calarco, R. et al

in Journal of Crystal Growth (2006), 289(1), 381-386

Morphology and optical properties of GaN nanowhiskers grown by molecular beam epitaxy(MBE) have been studied in correlation with growth parameters. It was shown that the growth parameters can be tuned ... [more ▼]

Morphology and optical properties of GaN nanowhiskers grown by molecular beam epitaxy(MBE) have been studied in correlation with growth parameters. It was shown that the growth parameters can be tuned such that uniform, well separated and high-quality nanowhiskers are obtained. Using an optimized ramp of Ga beam equivalent pressure (BEP) during the growth, the tapering or coalescence of nanowhiskers can be suppressed. By increasing the growth temperature the density of nanowhiskers is reduced, but the crystalline quality is improved as can be concluded from cathodoluminescence (CL) results. [less ▲]

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See detailAn AlGaN/GaN two-color photodetector based on AlGaN/GaN/SiC HEMT layer structure
Marso, Michel UL; Fox, A.; Heidelberger, G. et al

in Physica Status Solidi C. Current Topics in Solid State Physics (2006), 3(6), 2261-2264

The optoelectronic properties of MSM diodes that are based on an AlGaN/GaN HEMT layer system are investigated as function of the applied bias. For low voltages, the two-dimensional electron gas acts as a ... [more ▼]

The optoelectronic properties of MSM diodes that are based on an AlGaN/GaN HEMT layer system are investigated as function of the applied bias. For low voltages, the two-dimensional electron gas acts as a barrier for the depletion layer. Therefore, only the upper AlGaN barrier layer contributes to the photocurrent. In the high voltage regime the depletion region penetrates the GaN buffer that adds the spectral responsivity of GaN to the pure AlGaN behaviour in the low voltage regime. The ratio of the responsivities at 350 nm and 300 nm wavelength can be switched from 0.01 at 2.5 V to 0.8 at 4 V bias. This property makes the MSM-2DEG a candidate for use as two-color photodetector. Device fabrication uses standard HEMT processing steps, allowing integration in HEMT circuits without the need of sophisticated growth or etching techniques. [less ▲]

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See detailTerahertz-Radiation Photomixers on Nitrogen-Implanted GaAs, (2006) 117 - 120
Mikulics, M.; Marso, Michel UL; Stanček, S. et al

in Proc. 6th Intern. Conf. Advanced Semicon. Dev. & Microsystems ASDAM’06 (2006)

We have fabricated and characterized photomixers based on high energy nitrogen-ion-implanted GaAs. For material optimization and annealing dynamics in MSM photodetector structures, we used 400 keV ... [more ▼]

We have fabricated and characterized photomixers based on high energy nitrogen-ion-implanted GaAs. For material optimization and annealing dynamics in MSM photodetector structures, we used 400 keV implantation energy with an ion dose of 1´1016 cm-2. For photomixer structures we used 3 MeV energy to implant N+ ions into GaAs substrates, with an ion concentration dose of 3´1012 cm-2. The N+-implanted GaAs photomixers exhibit improved output power in comparison to their counterparts, photomixers fabricated on low-temperature-grown GaAs. The highest output power was 2.6 μW at 850 GHz and about 1 μW at 1 THz. No saturation of the output power with increased bias voltage and optical input power was observed. These characteristics make N+-implanted GaAs the material of choice for efficient high power sources of terahertz radiation. [less ▲]

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See detailDefect Distribution along Single GaN Nanowhiskers
Cavallini, Anna; Polenta, Laura; Rossi, Marco et al

in Nano Letters (2006), 6(7), 1548-1551

In this letter we report on spectral photoconductivity (PC) on different sections of single MBE-grown GaN nanowhiskers of diameters ranging on the order of 100 nm. The photoconductivity spectra show ... [more ▼]

In this letter we report on spectral photoconductivity (PC) on different sections of single MBE-grown GaN nanowhiskers of diameters ranging on the order of 100 nm. The photoconductivity spectra show, besides the band-gap related transition, deep-levels corresponding to the yellow, green, and blue bands. A strong spatial localization of specific photocurrent peaks has been observed, indicating that the defects responsible for such transitions are distributed inhomogeneously along the column growth direction. [less ▲]

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See detailTraveling-wave photomixer with recessed interdigitated contacts on low-temperature-grown GaAs
Mikulics, M.; Michael, E. A.; Schieder, R. et al

in Applied Physics Letters (2006), 88(4), 0411181-0411183

We have fabricated and characterized novel traveling-wave photomixers with recessed interdigitated metal-semiconductor-metal MSM contacts based on low-temperature-grown GaAs. The new recessed MSM geometry ... [more ▼]

We have fabricated and characterized novel traveling-wave photomixers with recessed interdigitated metal-semiconductor-metal MSM contacts based on low-temperature-grown GaAs. The new recessed MSM geometry led to an improved electric-field distribution inside the photomixer structure and resulted in an up-to-100% increase in the output power of continuously operated devices, compared to conventional MSM devices with standard surface electrodes fabricated on an identical material. The recessed electrode structure also resulted in lower saturation of output power at higher input powers, enabling it to take advantage of higher input powers. [less ▲]

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See detailUltrafast and Highly-Sensitive Photodetectors with Recessed Electrodes Fabricated on Low-Temperature-Grown GaAs
Mikulics, M.; Wu, S.; Marso, Michel UL et al

in IEEE Photonics Technology Letters (2006), 18 (2006)(5-6), 820-822

We have fabricated and characterized ultrafast metal–semiconductor–metal (MSM) photodetectors with recessed electrodes, based on low-temperature-grown GaAs. The new recessed-electrode MSM geometry led to ... [more ▼]

We have fabricated and characterized ultrafast metal–semiconductor–metal (MSM) photodetectors with recessed electrodes, based on low-temperature-grown GaAs. The new recessed-electrode MSM geometry led to an improved electric-field distribution inside the photodetector structure and resulted in a 25% breakdown voltage and sensitivity increase with simultaneous four-fold reduction of capacitance, as compared to the identical MSM devices with planar electrodes. Time-resolved studies performed using 100-fs-duration laser pulses showed that recessed-electrode MSMs exhibited 1.0-ps-wide photoresponse transients with no slow after-pulse tails and their photoresponse time was 0.9 ps. The improved transient photoresponse parameters are the main advantages of the recessed-electrode geometry. [less ▲]

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See detailTraveling-wave photomixers fabricated on high energy nitrogen-ion-implanted GaAs
Mikulics, M.; Michael, E. A.; Marso, Michel UL et al

in Applied Physics Letters (2006), 89(7), 071103

The authors report on fabrication and measurement of traveling-wave photomixers based on high energy and low dose nitrogen-ion-implanted GaAs. They used 3 MeV energy to implant N+ ions into GaAs ... [more ▼]

The authors report on fabrication and measurement of traveling-wave photomixers based on high energy and low dose nitrogen-ion-implanted GaAs. They used 3 MeV energy to implant N+ ions into GaAs substrates with an ion concentration dose of 3 1012 cm−2. The N+-implanted GaAs photomixers exhibit improvements in the output power in comparison with their counterparts, photomixers fabricated on low-temperature-grown GaAs. The maximal output power was 2.64 W at 850 GHz. No saturation of the output power with increased bias voltage and optical input power was observed. These characteristics make N+-implanted GaAs the material of choice for efficient high power sources of terahertz radiation. [less ▲]

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See detailComparison of AlGaN/GaN MSM Varactor Diodes Based on HFET and MOSHFET Layer Structures
Marso, Michel UL; Fox, A.; Heidelberger, G. et al

in IEEE Electron Device Letters (2006), 27

In this letter, the performance of AlGaN/GaN-based metal–semiconductor–metal (MSM) varactor diodes based on HFET and MOSHFET layer systems is investigated. Passivated HFET MSM devices are coated with a 10 ... [more ▼]

In this letter, the performance of AlGaN/GaN-based metal–semiconductor–metal (MSM) varactor diodes based on HFET and MOSHFET layer systems is investigated. Passivated HFET MSM devices are coated with a 10-nm-thick SiO2 layer between the electrodes; in MOSHFET-based diodes, this layer is also used as an insulator underneath the gate. Device fabrication uses standard HFET fabrication technology, allowing easy integration in monolithic microwave integrated circuits. Devices with different electrode geometry are characterized by direct current and by S-parameter measurements up to 50 GHz. The HFET-based varactors show capacitance ratios up to 14 and cutoff frequencies up to 74 GHz. The MOSHFET-based devices, on the other hand, show lower capacitance ratios and poorer stability because of the insulation layer between electrodes and semiconductor. [less ▲]

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See detailImpact of surface treatment under the gate on the current collapse of unpassivated AlGaN/GaN heterostructure field-effect transistors
Kordoš, P.; Bernát, J.; Gregušová, D. et al

in Semiconductor Science & Technology (2006), 21 (2006)

Unpassivated GaN/AlGaN/GaN/SiC heterostructure field-effect transistors were fabricated on intentionally undoped and 5 × 1018 cm−3 modulationdoped material structures. The influence of surface treatment ... [more ▼]

Unpassivated GaN/AlGaN/GaN/SiC heterostructure field-effect transistors were fabricated on intentionally undoped and 5 × 1018 cm−3 modulationdoped material structures. The influence of surface treatment before gate metallization on the gate leakage and drain current collapse of the devices was observed. In the case of a short HCl treatment (∼5 s), a relatively small gate leakage (<10−6A mm−1 at −6 V gate bias) but large current collapse (∼30% after applying 5 μs wide pulses) were measured. On the other hand, devices with a longer surface treatment (15–20 s) showed an increased gate leakage (>10−4A mm−1) and a simultaneously negligible current collapse (<5%). This effect is qualitatively similar in devices prepared on the undoped and doped heterostructures. It is assumed that a thin interfacial oxide layer under the gate might be responsible for a lower leakage current and a larger current collapse of the devices. [less ▲]

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See detailComparative study on unpassivated and passivated AlGaN/GaN HFETs and MOSHFETs
Heidelberger, G.; Bernát, J.; Gregušová, D. et al

in Physica Status Solidi A. Applications and Materials Science (2006), 203(7), 1876-1881

In this comparative study we investigate AlGaN/GaN-based unpassivated and passivated HFETs and MOSHFETs with regards to DC-, RF-, and power-performance. For optimal comparability, all devices emanate from ... [more ▼]

In this comparative study we investigate AlGaN/GaN-based unpassivated and passivated HFETs and MOSHFETs with regards to DC-, RF-, and power-performance. For optimal comparability, all devices emanate from the same wafer consisting of a SiC-substrate, a 3 μm GaN- and a 30 nm Al0.28Ga0.72N-layer. Devices are processed simultaneously to a large extend. Passivated devices are coated with a 10 nm thick SiO2-layer between the electrodes, MOSHFETs contain a 10 nm thick SiO2-layer serving as gate-insulator underneath the gate and as conventional passivation-layer between the electrodes. Unpassivated devices serve as reference. We present empirical evidence that MOSHFETs outperform both the conventional and the passivated HFETs with respect to DC-, RF-, and power-performance, and we point out the different mechanisms responsible for the behaviour of the devices. [less ▲]

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See detailGaAs photodetectors prepared by high-energy and high-dose nitrogen implantation
Mikulics, Martin; Marso, Michel UL; Mantl, Siegfried et al

in Applied Physics Letters (2006), 89

The authors report on the fabrication and characterization of photodetectors based on nitrogen-ion-implanted GaAs and the annealing dynamics in these devices. An energy of 400 keV was used to implant N ... [more ▼]

The authors report on the fabrication and characterization of photodetectors based on nitrogen-ion-implanted GaAs and the annealing dynamics in these devices. An energy of 400 keV was used to implant N ions in a GaAs substrate at an ion concentration of 1 1016 cm−2. Dark current measurements as well as measurements under illumination show that the material properties rapidly change during the annealing process. Photodetectors based on nitrogen-implanted GaAs materials with annealing temperatures up to 400 °C exhibit a subpicosecond carrier lifetime up to 0.6 ps. These properties make nitrogen-ion-implanted GaAs an ideal material for ultrafast photodetectors, as alternative to low-temperature-grown GaAs. [less ▲]

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See detailComparison of AlGaN/GaN MSM varactor diodes based on HFET and MOSHFET layer structures
Marso, Michel UL; Fox, A.; Heidelberger, G. et al

in Proc. 6th Intern. Conf. Advanced Semicon. Dev. & Microsystems ASDAM’06 (2006)

In this comparative study we investigate the performance of AlGaN/GaN based MSM varactor diodes based on HFET and MOSHFET layer systems. Device fabrication uses standard HFET fabrication technology ... [more ▼]

In this comparative study we investigate the performance of AlGaN/GaN based MSM varactor diodes based on HFET and MOSHFET layer systems. Device fabrication uses standard HFET fabrication technology, allowing easy integration in MMICs. Devices with different electrode geometries are characterized by DC and by S-parameter measurements up to 50 GHz. The HFET based varactors show capacitance ratios up to 14. The MOSHFET based devices, on the other hand, exhibit lower capacitance ratios and poorer stability because of theinsulation layer between electrodes and semiconductor. [less ▲]

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