Wogong Zhang

GeSn-on-Si normal incidence photodetectors with bandwidths more than 40 GHz.

GeSn (Sn content up to 4.2%) photodiodes with vertical pin structures were grown on thin Ge virtual substrates on Si by a low temperature (160 °C) molecular beam epitaxy. Vertical detectors were fabricated by a double mesa process with mesa radii between 5 µm and 80 µm. The nominal intrinsic absorber contains carrier densities from below 1 · 10(16) cm(-3) to 1 · 10(17) cm(-3) for Ge reference detectors and GeSn detectors with 4.2% Sn, respectively. The photodetectors were investigated with electrical and optoelectrical methods from direct current up to high frequencies (40 GHz). For a laser wavelength of 1550 nm an increasing of the optical responsivities (84 mA/W -218 mA/W) for vertical incidence detectors with thin (300 nm) absorbers as function of the Sn content were found. Most important from an application perspective all detectors had bandwidth above 40 GHz at enough reverse voltage which increased from zero to -5 V within the given Sn range. Increasing carrier densities (up to 1 · 10(17) cm(-3)) with Sn contents caused the depletion of the nominal intrinsic absorber at increasing reverse voltages.

The Zener-Emitter: A novel superluminescent Ge optical waveguide-amplifier with 4.7 dB gain at 92 mA based on free-carrier modulation by direct Zener tunneling monolithically integrated on Si

We report on the first experimental demonstration of a monolithic integrated Group-IV Ge semiconductor optical amplifier (SOA) — the Ge Zener-Emitter (ZE). The ZE is a device featuring light amplification up to 4.7 dB (92 mA) at center wavelength of 1700 nm and gain-bandwidth of 98 nm on Si (100). Our novel direct Zener band-to-band tunneling (BTBT) injection method enables low-voltage electron emission beyond the Boltzmann-limit (38 mV/dec at 1.55 K, 88 mV/dec at 300 K), achieving population-inversion at 0.45 V (41 mA). The ZE possesses a Si-Ge-Si hetero-structure with excellent CMOS integration compatibility by planar device design (550 nm) and an ultra-thin (100 nm) Ge virtual substrate (VS) on Si (100). Moreover, the ZE shows superior light emission properties with pulsed lasing at 1667 nm and superluminescent LED characteristic (150 cm−1 max. gain at 270 K, 100 cm−1 max. gain at 300 k). The developed ZE device presents a promising feature to monolithic Si-photonics filling the gap for energy-efficient light emission and amplification in a small footprint (1 mm) integrated waveguide-amplifier.

S-parameter characterization and lumped-element modelling of millimeter-wave single-drift impact-ionization avalanche transit-time diode

Five silicon (Si) p++–n−–n++ samples were grown at various doping concentrations (1.0 × 1017–2.2 × 1017 cm−3) in an n− layer by using the reduced-pressure CVD technique. By using these samples, 30 × 2 µm2 single-drift (SD) impact-ionization avalanche transit-time (IMPATT) diodes were processed with Si-based monolithic millimeter-wave integrated circuit (SIMMWIC) technology.1 , 2 ) The samples within a small process window exhibited a large negative differential resistance at approximately the avalanche frequency, as confirmed by small-signal S-parameter characterization. A model based on depletion width was given to explain the conditions for the appearance of the negative differential IMPATT resistance, which is the basis of millimeter-wave amplifier and oscillator applications. Furthermore, a measurement-based small-signal lumped-element model was established to describe the IMPATT functionality from the circuit component aspect. This lumped-element model shows a negative differential resistance within a well-defined range in the given element parameters, which can explain the experimental observations.

SIMMWIC integration of millimeter-wave antenna with two terminal devices for medical applications

Integration of planar antenna structures with oscillators and rectifiers, respectively, was performed an low loss, high resistivity silicon substrates. IMPATT diodes and special Schottky diodes operated in Mott mode were monolithically integrated in the planar waveguide circuit for mm-wave operation in the W-band (silicon monolithic mmwave integrated circuit-SIMMWIC ). Small chip sizes below 30mm2 could be obtained to meet requirement for medical endoscopes.

Systematic characterization of Silicon IMPATT diode for Monolithic E-band amplifier design

A systematic characterization procedure of Silicon IMPATT (IMPact ionization Avalanche Transit-Time) diode is introduced in this work. DC characterization consists of current-voltage (I-V) and capacity-voltage (C-V) measurements. RF small signal characterization is performed by the vector network analyzer (VNA). By combining the measured S-parameters of the 30×2 μm2 IMPATT diode and simulated data of a short ended coplanar waveguide (CPW), an E-band amplifier design flow based on SIMMWIC (Silicon Monolithic mm-Wave Integrated Circuits) technology is as proof of concept presented. According to the simulation results, the maximum gain of the designed amplifier achieves 34.4 dB at 67.8 GHz with 30 mA biasing current. With different biasing currents (20 ~ 40 mA) the avalanche frequency of the embedded IMPATT diode could be varied from 71.3 GHz to 91.5 GHz. This leads to an 8.6 GHz (62.8 ~ 71.4 GHz) dynamic tuning range of the amplification frequency.

Small-signal IMPATT diode characterization for mm-wave power generation in monolithic scenarios

concretely aiming at the efficient millimeter-wave power generation for monolithically integrated design, the small-signal S-parameter characterization of the impact-ionization avalanche transit-time (IMPATT) diodes was presented in this work. By combining the measured S-parameter data both of the 40 × 2 μm2 IMPATT diode and different short ended coplanar waveguide (CPW) structures, a designing-by-characterizing procedure was demonstrated for a monolithic E-band IMPATT oscillator. In spite of much less tuning freedom compared with the conventional discrete design, the Kurokawa condition for steady oscillation using IMPATT diode as active device was still well caught and comprehensively demonstrated by all characterized data. According to measured amplification spectra, the oscillation condition was optimally met at 70.54 GHz under the biasing condition of 37.11 mA for the finalized oscillator, which agrees well with the design prediction. Without any extra cooling element, which is a must for conventional discrete design, the monolithic IMPATT oscillator (~ 0.2 mm2) was functional free of damage over 20 minutes under continuous-wave (CW) biasing modus.

S-parameter based device-level C-V measurement of p-i-n single-drift IMPATT diode for millimeter-wave applications

Two different approaches of capacitance-voltage (C-V) measurement were applied to the fabricated single-drift (SD) impact-ionization avalanche transit-time (IMPATT) structures. From both the C-V results, the carrier concentrations of depleted space-charge-region (SCR) width characteristics were calculated. According to the epitaxial thickness and the doping concentration of the lightly n-doped layer, the approach applied to a 30 × 2 μm2 IMPATT device, which is based on small-signal S-parameter characterization (0.04-40 GHz), showed better agreement compared with the approach applied to a C-V structure (0.64 mm2) using the conventional low frequency (1 MHz) C-V instrument. Additionally, the E-band IMPATT operation of the 30 × 2 μm2 device has been well modelled with the capacitance value extracted from the S-parameter based C-V measurement. The good agreement between device modelling and measurement within frequency range 0.04-110 GHz shows the reliability of the small-signal S-parameter device-level C-V measurement for real mm-wave application scenarios.

S-Parameter Characterization and Lumped-Element Modelling of mm-Wave Single-Drift IMPATT Diode

Mm-wave single-drift impact avalanche transit-time (IMPATT) diodes were grown by using reduced-pressure chemical vapor deposition (CVD) and processed with silicon-based monolithic mm-wave integrated circuits (SIMMWIC) technology. The IMPATT-behavior was evaluated with small-signal S-parameter measurement up to 110 GHz. The avalanche frequency follows roughly √J-proportionality as proven for all samples. Samples within a small process window exhibited large negative differential resistance around avalanche frequency, which is the base for mm-wave amplifier and oscillator applications. A broad-band lumped-element model shows good agreement with the measured data and explains the overall principle for the functionality of selected samples.

A monolithic integrated 85 GHz schottky rectenna with dynamic tuning range of the conversion voltage

In this paper, the latest research results for design and characterization of an 85 GHz fully monolithic integrated schottky rectenna (rectifying antenna) using SiMMWIC (Silicon Monolithic Mm-Wave Integrated Circuits) technology are presented. Under RF excitation in frequency range of 75 ~ 90 GHz a sharp receiving profile at 85 GHz of the designed rectenna is clearly characterized. With different bias currents (0.1 μA ~ 0.44 mA) the working point of the embedded schottky diode (cut-off frequency ~ 0.5 THz at 0 V) could be dynamically tuned for the optimal conversion voltage. The corresponding tuning range of the conversion voltage could be varied from 1 mV to 17 mV at 85 GHz.

A reliable 40 GHz opto-electrical system for characterization of frequency response of Ge PIN photo detectors

This study presents calibration of a self-built 40 GHz measurement setup using vector network analyzer and Mach-Zehnder modulator. The setup is used for frequency response characterization of Ge PIN photodetectors.