Direct electro-optical pumping for hybrid CdSe nanocrystal/III-nitride based nano-light-emitting diodes

in Applied Physics Letters (2016), 108

We propose a device concept for a hybrid nanocrystal/III-nitride based nano-LED. Our approach is based on the direct electro-optical pumping of nanocrystals (secondary excitation) by electrically driven ... [more ▼]

We propose a device concept for a hybrid nanocrystal/III-nitride based nano-LED. Our approach is based on the direct electro-optical pumping of nanocrystals (secondary excitation) by electrically driven InGaN/GaN nano-LEDs as the primary excitation source. To this end, a universal hybrid optoelectronic platform was developed for a large range of optically active nano- and mesoscopic structures. The advantage of the approach is that the emission of the nanocrystals can be electrically induced without the need of contacting them. The proof of principal was demonstrated for the electro-optical pumping of CdSe nanocrystals. The nano-LEDs with a diameter of 100 nm exhibit a very low current of 8 nA at 5V bias which is several orders of magnitude smaller than for those conventionally used. The leakage currents in the device layout were typically in the range of 8 pA to 20 pA/cm2 at 5V bias. The photon-photon down conversion efficiency was determined to be 27%. Microphotoluminescence and microelectroluminescence characterization demonstrate the potential for future optoelectronics and highly secure “green” information technology applications. [less ▲]

Numerical study of high impedance T-match antennas for terahertz photomixers

in Optical and Quantum Electronics (2015), 47

This paper outlines an efficient numerical method to design terahertz photomixers. The simulations are benchmarked using measured power levels from results published in the literature. Next, the method is ... [more ▼]

This paper outlines an efficient numerical method to design terahertz photomixers. The simulations are benchmarked using measured power levels from results published in the literature. Next, the method is applied to two new photomixer designs based on the high impedance T-match antenna with bias supply DC-blocking structures for either a uniplanar layout or amultilayer structure for improved device reliability. Manufacturability is favoured by avoiding the use of airbridges, substrate thinning or under-etching. The estimated output power of the improved design is 9.0μW, which is an improvement of three times over the reference photomixer. [less ▲]

III-nitride nano-LEDs for single photon lithography

in Conference Proceedings The 10th International Conference on Advanced Semiconductor devices and Microsystems (2014, October)

We fabricated and tested III-nitride (p-GaN/MQW/n-GaN/sapphire) based nano-LEDs designed for operation in the single photon lithography technique. The band edge luminescence energy of the III-nitride nano ... [more ▼]

We fabricated and tested III-nitride (p-GaN/MQW/n-GaN/sapphire) based nano-LEDs designed for operation in the single photon lithography technique. The band edge luminescence energy of the III-nitride nano-LEDs depends linearly on the structure size. Our studies provide clear evidence that our technological process for the vertically integrated nano-LED emitters is perfectly suited for long term operation without any indication of degradation effects. This novel technology shows strong potential for a future flexible single photon lithography [1] which is applicable for molecular photonic and electronic circuits. [less ▲]

Novel Double-Level-T-Gate Technology

in Conference Proceedings The 10th International Conference on Advanced Semiconductor devices and Microsystems (2014, October)

We developed a novel double-level-T-gate technology based on wet etching of a metal gate interlayer. With the help of this technological process we prepared T-gate feet with widths as small as 200 nm. The ... [more ▼]

We developed a novel double-level-T-gate technology based on wet etching of a metal gate interlayer. With the help of this technological process we prepared T-gate feet with widths as small as 200 nm. The major advantage of our process is its use of only standard optical lithography. It allows the fabrication of 100 nanometer size T-gates for transistors. High electron mobility transistors (HEMTs) were fabricated on an AlGaN/GaN/sapphire material structure with an original gate length Lg of 2 μm. Their cutoff frequency of 6 GHz was improved to 60 GHz by etching the gate to a 200 nm length double T-gate contact. [less ▲]

Highly Transparent Conducting Polymer Top Contacts for Future III–Nitride Based Single Photon Emitters

in Japanese Journal of Applied Physics (2013), 52

Tuning the spectral sensitivity of vertical InN nanopyramid based photodetectors by means of band gap engineering and/or nanostructure size control

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 ▲]

Non-uniform distribution of induced strain in gate-recessed AlGaN/GaN structure evaluated by micro-PL measurements

in Semiconductor Science and Technology (2012), 27(10), 105008-105008

Micro-photoluminescence (μ-PL) studies were performed on AlGaN/GaN heterostructure field effect transistors (HFETs) with different gate-recessing depths. It was found that μ-PL is the method of choice for ... [more ▼]

Micro-photoluminescence (μ-PL) studies were performed on AlGaN/GaN heterostructure field effect transistors (HFETs) with different gate-recessing depths. It was found that μ-PL is the method of choice for detecting dry etching damage and simultaneously recording strain and stress in the HFET GaN layer. Lateral sub-μm resolved mapping shows that the strain in the GaN layer after recessing is partially relaxed and non-uniform. [less ▲]

Comparison of AlGaN/GaN HFETs and MOSHFETs in prospect of oscillator design

in The Eighth International Conference on Advanced Semiconductor Devices and Microsystems, ASDAM 2010 (2010)

Finite element simulation of metal-semiconductor-metal photodetector

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