A. Poloczek

High-Speed GaN/GaInN Nanowire Array Light-Emitting Diode on Silicon(111)

The high speed on-off performance of GaN-based light-emitting diodes (LEDs) grown in c-plane direction is limited by long carrier lifetimes caused by spontaneous and piezoelectric polarization. This work demonstrates that this limitation can be overcome by m-planar core-shell InGaN/GaN nanowire LEDs grown on Si(111). Time-resolved electroluminescence studies exhibit 90-10% rise- and fall-times of about 220 ps under GHz electrical excitation. The data underline the potential of these devices for optical data communication in polymer fibers and free space.

Effect of contaminations and surface preparation on the work function of single layer MoS2

Summary Thinning out MoS2 crystals to atomically thin layers results in the transition from an indirect to a direct bandgap material. This makes single layer MoS2 an exciting new material for electronic devices. In MoS2 devices it has been observed that the choice of materials, in particular for contact and gate, is crucial for their performance. This makes it very important to study the interaction between ultrathin MoS2 layers and materials employed in electronic devices in order to optimize their performance. In this work we used NC-AFM in combination with quantitative KPFM to study the influence of the substrate material and the processing on single layer MoS2 during device fabrication. We find a strong influence of contaminations caused by the processing on the surface potential of MoS2. It is shown that the charge transfer from the substrate is able to change the work function of MoS2 by about 40 meV. Our findings suggest two things. First, the necessity to properly clean devices after processing as contaminations have a great impact on the surface potential. Second, that by choosing appropriate materials the work function can be modified to reduce contact resistance.

High-speed picosecond pulse response GaNAsSb p-i-n photodetectors grown by rf plasma-assisted nitrogen molecular beam epitaxy

The authors report on picosecond pulse response GaNAsSb∕GaAs p-i-n photodetectors grown by molecular beam epitaxy in conjunction with a rf plasma-assisted nitrogen source. The 2μm thick GaNAsSb photoabsorption layer contains 3.3% of N and 8% of Sb resulting in a dc photoresponse up to 1380nm wavelength. Dark current densities at 0 and −5V are 1.6×10−5 and 13A∕cm2, respectively. The GaNAsSb photodiodes exhibit a record pulse response width of only 40.5ps (full width at half maximum) corresponding to a 4.5GHz bandwidth.

14-GHz GaNAsSb Unitraveling-Carrier 1.3-

We report on picosecond pulsed response and 3-dB cutoff frequency of 1.3-mum GaNAsSb unitraveling-carrier photodetectors (PDs) grown by molecular beam epitaxy using a radio-frequency plasma-assisted nitrogen source. The 0.1-mum -thick GaNAsSb photoabsorption layer contains 3.5% of N and 9% of Sb, resulting in a bandgap of 0.88 eV. The dark current densities at 0 and -9 V are 6 and 34 mA/cm2, respectively. The GaNAsSb UTC PDs exhibit a temporal response width of 46 ps and a record 3-dB cutoff frequency of 14 GHz at -9 V.

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InP-based double-barrier resonant tunnelling diodes have been optimized for high speed digital circuits. We present the scalability of high current density (JP ≈ 150 kA/cm2;) resonant tunnelling diodes in the sub-micrometer electrode area range. A small signal equivalent circuit has been developed and its parameters are precisely deduced from DC and RF measurements. Based on this model the scalability has been investigated with emphasis on a low but also scalable series resistance in order to keep the peak voltage constant. A comparison of dry and wet etching methods in the device fabrication will be presented. A multiple mesa concept has been adopted to provide reliable scalability at low emitter area (AE < 1 µm2).

Photodetectors Grown by RF Plasma-Assisted Nitrogen Molecular Beam Epitaxy

An InGaAs pin-diode has been grown on (001) Si- substrate overcoming the lattice mismatch by introducing an III/V-quasi-buffer. The device high speed performance is demonstrated by BER measurements up to 10 Gbit/s.

Scalable high-current density RTDs with low series resistance

We report on the fabrication of high-speed GaNAsSb photodetector for multigigabit operation at 1.3μm wavelength. The 2μm thick bulk GaNAsSb photoabsorption layer contains 3.3% of N and 8% of Sb, resulting in optical band gap of ∼0.9eV suitable for near infrared operation up to wavelengths of about 1380nm. By using the bulk photoabsorption layer, we have fabricated GaNAsSb photodetector with high dc responsivity of 0.12A∕W at 1.3μm wavelength. The photodetector exhibits 3dB cutoff frequency at 1.3μm wavelength of 4.5GHz. Furthermore, 5Gb∕s fiber-optic transmission at 1.3μm wavelength is demonstrated using the GaNAsSb photodetector.

Integrated InGaAs pin-diode on exactly oriented silicon (001) substrate suitable for 10 Gbit/s digital applications

The application of resonant tunneling diodes (RTD) for generation of Gaussian-like monocycles and modified Hermite pulses of 2nd order for ultrawideband (UWB) impulse radio is investigated in this paper. A circuit concept employing a pin-photodiode and two RTD based monostable bistable threshold logic elements (MOBILE) is introduced. The circuit generates, depending on a digital optical input signal, arbitrary pulse cycles at the output of the circuit. Based on the measurement result of a single MOBILE, simulations are presented that show the capability of the proposed circuit to generate pulses like single Gaussian pulses, Gaussian monocycles, and 2nd-order modified Hermite pulses. Experimental verification of positive and negative gaussian pulses with a width of 100 ps is demonstrated for a pulse repetition rate of 13.2 Gpulses/s.

Multigigabit 1.3μm GaNAsSb∕GaAs Photodetectors

The co-integration of III/V devices such as InGaAsP PIN diode and an (In)AlAs/In(Ga)As Resonant Tunnelling Diodes with state-of-the-art silicon NMOS transistors is studied. The III/V devices layers are epitaxially grown and fabricated on silicon substrates for the extraction of model parameters. The performance of a potentially low-cost optical receiver circuit on silicon is simulated using HSPICE up to 10 Gb/s.

Sub-Nanosecond Pulse Generation using Resonant Tunneling Diodes for Impulse Radio

Recently, heavy emitter doping rather than decreasing the barrier thickness has boosted the peak current density of resonant tunneling diodes (RTDs) above 1,000 kA/cm2. Based on this achievement very mature InP-based RTD with current densities above 500 kA/cm2 are nowadays the leading solid-state THz device [1, 2]. Here, we show that even triple-barrier RTD (TBRTD) devices now reach a current density in excess of 250 kA/cm2 making this element ideally suited for rectification [3] but now at THz frequencies. Figure 1 is the state of art of THz detection sensitivity of previously reported zero bias detectors. Focusing on such zero bias broadband THz detection, we have also been studying on a design policy for a μm-sized on-chip self-complementally antenna and especially we have reported basic performances of a bow-tie antenna[4,5] integrated with a conventional homogeneous semiconductor mesa structure. However, it was still limited studies considering neither of actual nonlinear devices and peripheral circuits.