Towards future III-nitride based THz OEICs in the UV range

in ASDAM 2012, The Ninth International Conference on Advanced Semiconductor Devices and Microsystems (2012)

Improving output power of terahertz heterodyne photomixer by impedance matching

in ASDAM 2012, The Ninth International Conference on Advanced Semiconductor Devices and Microsystems (2012)

Electrical and structural characterization of AlGaN/GaN field-effect transistors with recessed gate

in Vacuum (2012), 86(6), 754-756

Performance of AlGaN/GaN heterostructure field-effect transistors (HFETs) with recessed gate was investigated and compared with non-recessed counterparts. Optimal dry etch conditions by plasma assisted Ar ... [more ▼]

Performance of AlGaN/GaN heterostructure field-effect transistors (HFETs) with recessed gate was investigated and compared with non-recessed counterparts. Optimal dry etch conditions by plasma assisted Ar sputtering were found for ~6 nm gate recess of a 20 nm thick AlGaN barrier layer. A decrease of the residual strain after the gate recessing (from -0.9 GPa to -0.68 GPa) was evaluated from the photoluminescence measurement. The saturation drain current at the gate voltage VG = 1 V decreased from 1.05 A/mm to 0.85 A/mm after the recessing. The gate voltage for a maximal transconductance (240-250 mS/mm) has shifted from -3 V for non-recessed HFETs to -0.2 V for recessed counterparts. Similarly, the threshold voltage increased after the gate recessing. A decrease of the sheet charge density from 1 x 10 13 cm-2 to4 x 10 12 cm-2 at VG = 0 V has been evaluated from the capacitance measurements. The RF measurements yielded a slight increase of the cut-off frequencies after the gate recessing. All these indicate that the gate recessing is a useful tool to optimize the AlGaN/GaN HFET performance for high-frequency applications as well as for the preparation of normally-off devices. [less ▲]

GaN for THz Sources

in Proceedings of SPIE, vol. 7945, pp. 79450Y-1 - 79450Y-9 (2011)

In this work we investigate two different approaches to generate THz radiation by the use of the unique electrical and thermal properties of GaN. One method is heterodyne photomixing, a compact and ... [more ▼]

In this work we investigate two different approaches to generate THz radiation by the use of the unique electrical and thermal properties of GaN. One method is heterodyne photomixing, a compact and inexpensive approach to generate continuous electromagnetic radiation in the terahertz range, with tuneable frequency. It uses two lasers with slightly different wavelengths that illuminate an ultrafast photoconductor. The interference of both laser beams generates a beat frequency of the illumination intensity in the terahertz range. One drawback of the conventionally used LT GaAs as ultrafast photoconductor material is the relatively low THz power in the nW to ?W range. The aim of our work is to increase the output power by replacing the LT GaAs with GaN. This semiconductor is rather known as basic material for blue LEDs and lasers, but it has also remarkable electrical and thermal properties that allow higher laser power and bias voltage. A more conventional, electronic approach to generate THz radiation consists in the fabrication of an oscillator circuit based on ultrafast transistors, e.g. Hetero Field Effect Transistors based on InGaAs. These circuits can be designed up to about 100 GHz oscillation frequency. The THz region is achieved by frequency multipliers, e.g. realized by very small-sized Schottky diodes. However, each multiplier stage considerable reduces the output power. In this field we investigate GaN based transistor devices to profit from the much better power performance of this material, compared to classical semiconductors. Devices in this material system are usually used for high power applications at moderate frequencies, but the very high electron saturation velocity of GaN allows the application above 100 GHz as well. [less ▲]

Femtosecond and highly sensitive GaAs metal–semiconductor–metal photodetectors grown on aluminum mirrors/pseudo-substrates,

in Semiconductor Science and Technology (2010), 25(7), 75001

Quantum transport in narrow-gap semiconductor nanocolumns

in Physica Status Solidi C. Current Topics in Solid State Physics (2010), 7(2), 386-389

Finite element simulation of metal-semiconductor-metal photodetector

in Solid-State Electronics (2009), 53(10), 1144-1148

Das Spektrum der elektromagnetischen Strahlung: Technische Nutzung und Herausforderungen

in Revue Technique Luxembourgeoise (2009), (4), 36-37

Sensitivity enhancement of metal-semiconductor-metal photodetectors on low-temperature-grown GaAs using alloyed contacts

in IEEE Photonics Technology Letters (2008), 20(12), 1054-1056

We have fabricated and characterized metal–semiconductor–metal (MSM) photodetectors based on lowtemperature-grown GaAs with alloyed (i.e., ohmic-type) contacts. The annealed contacts optimize the electric ... [more ▼]

We have fabricated and characterized metal–semiconductor–metal (MSM) photodetectors based on lowtemperature-grown GaAs with alloyed (i.e., ohmic-type) contacts. The annealed contacts optimize the electric field distribution inside the photodetector structure which results in an up-to-200% responsivity increase of the devices, compared to conventional MSM detectors with standard nonalloyed (Schottky-type) metallization fabricated on identical material. The improved MSM device with alloyed contacts shows more than three times larger output amplitude at illumination with a 100-fs Ti : sapphire laser, compared to the nonalloyed devices, without degradation of detector speed. [less ▲]

Doping Concentration of GaN Nanowires Determined by Opto-Electrical Measurements

in Nano Letters (2008), 8(9), 3056-3059

The influence of n-doping on the electrical transport properties of GaN nanowires is investigated by photoconductivity measurements on wires with different diameters. The electrical transport in nanowires ... [more ▼]

The influence of n-doping on the electrical transport properties of GaN nanowires is investigated by photoconductivity measurements on wires with different diameters. The electrical transport in nanowires is extremely sensitive to the wire diameter because of the size dependent barrier for surface recombination. This effect is used to determine the doping level of the nanowires and to complete and consolidate our previously developed surface recombination model for GaN nanowires. [less ▲]