Davide Saguatti

Efficiency droop in InGaN/GaN blue light-emitting diodes: Physical mechanisms and remedies

Physical mechanisms causing the efficiency droop in InGaN/GaN blue light-emitting diodes and remedies proposed for droop mitigation are classified and reviewed. Droop mechanisms taken into consideration are Auger recombination, reduced active volume effects, carrier delocalization, and carrier leakage. The latter can in turn be promoted by polarization charges, inefficient hole injection, asymmetry between electron and hole densities and transport properties, lateral current crowding, quantum-well overfly by ballistic electrons, defect-related tunneling, and saturation of radiative recombination. Reviewed droop remedies include increasing the thickness or number of the quantum wells, improving the lateral current uniformity, engineering the quantum barriers (including multi-layer and graded quantum barriers), using insertion or injection layers, engineering the electron-blocking layer (EBL) (including InAlN, graded, polarization-doped, and superlattice EBL), exploiting reversed polarization (by either inv...

Investigation of Efficiency-Droop Mechanisms in Multi-Quantum-Well InGaN/GaN Blue Light-Emitting Diodes

Efficiency-droop mechanisms and related technological remedies are critically analyzed in multi-quantum-well (QW) InGaN/GaN blue light-emitting diodes by means of numerical device simulations and their comparison with experimental data. Auger recombination, electron leakage, and incomplete QW carrier capture can separately produce droop effects in quantitative agreement with experimental data, but “extreme” values, at the limit of or outside their generally accepted range, must be imposed for related droop-controlling parameters. Less stringent conditions are needed if combinations of the aforementioned mechanisms are assumed to act jointly. Applying technological/structural modifications like QW thickness or number increase and barrier p-type doping leads to distinctive effects on droop characteristics depending on the assumed droop mechanism. Increasing the QW number appears, in particular, to be the most effective droop remedy in case the phenomenon is induced by Auger recombination. Possible technology-dependent variation of droop-controlling parameters and/or multiple droop mechanisms can, however, make discrimination of droop origin on the basis of the effects of applied technological remedies very difficult.

Design and Characterization of Current-Assisted Photonic Demodulators in 0.18-

We report on the design of a current-assisted photonic demodulator (CAPD) using standard 0.18-μm complementary metal-oxide-semiconductor technology and its electrooptical characterization. The device can perform both light detection and demodulation in the charge domain, owing to a drift field generated in the silicon substrate by a majority carrier flow. Minimum-sized 10 × 10 μm2 CAPDs exhibit a direct-current charge-transfer efficiency larger than 80% (corresponding to demodulation contrast larger than 40% under sine-wave modulation) at the modest power consumption of 10 μW and a 3-dB bandwidth of >; 45 MHz. An excellent linearity value with an error lower than 0.11% is obtained in phase measurements. CAPDs with optimized modulation electrode geometries are finally designed, aiming at an improved contrast-versus-power tradeoff.

\mu\hbox{m}

This paper presents a Novel low noise, high breakdown InAlAs/InGaAs pseudomorphic High Electron Mobility Transistors (pHEMTs). The improvements in breakdown voltage are brought about by a judicious combination of epitaxial layer design and field plate techniques. No significant degradations of DC and RF characteristics are observed for devices with field plate structures. An outstanding improvement in breakdown voltages of >30% is attained by field plate devices which should allow their usage in efficient high-added power efficiency amplifiers design.

CMOS Technology

Wireless alpha-ray device has been designed, realized and tested in operation. The first prototype is a battery-supplied system with a compact package and wireless communication capability. One of the more attractive features is its ability to operate in a star network (single point-to-multipoint). The sensor records the arrival time of the alpha particles and the spectrum of the produced charge; it transmits this information in regular time intervals or upon request to the base station. The overall system has a compact package suitable for remote alpha-ray spectroscopy.

Fabrication of novel high frequency and high breakdown InAlAs-InGaAs pHEMTs

An autonomous Radon sensor with wireless connectivity has been developed, using a BJT detector on high-resistivity silicon as alpha-particle detector. Charged Radon daughters are collected on the detector surface electrostatically. Thanks to the BJT internal amplification, real-time alpha particle detection is made possible using a very simple readout electronics which records alpha-particle arrival time and charge. Functional tests at known Radon concentrations demonstrated a sensitivity up to 4.9 cph/(100 Bq/m3), which translates into the capability of detecting a Radon concentration of 200±20 Bq/m3 and 500±50 Bq/m3 after 10 and 4 h, respectively. The count rate at nominally-zero Radon concentration was 0.05 cph.

A 2.4-GHz wireless alpha-ray sensor for remote monitoring and spectroscopy

High-voltage InGaAs-InAlAs HEMTs featuring optimized field-plate structures are being developed. A TCAD approach has been adopted for their design. Two-dimensional device simulations have preliminarily been calibrated by comparison with DC and RF measurements from the baseline InP HEMT technology into which the field plate is being incorporated. Simulations have then been used to design field-plate structures with optimal length and passivation thickness.