Effect of Anodic Oxidation on the Characteristics of Lattice-Matched AlInN/GaN Heterostructures

The effect of anodic oxidation on the electronic characteristics of lattice-matched AlInN/GaN heterostructures was investigated using field-effect transistor (FET) structures with the gate areas in direct contact with the electrolytes. The gate surface of the FETs was subjected to anodic oxidation in 0.1 M KOH. The oxidized heterostructures were analyzed by electrochemical impedance spectroscopy and by modeling the characteristics of the electrolyte-gate FETs and the energy-band diagram of the heterostructures. This analysis suggested that the anodic treatment induced a bulk oxidation of the AlInN barrier. The Fermi level at the oxidized AlInN surface was shifted deep into the bandgap. The oxidation led to a reduction of the carrier mobility and to partial depletion of the channel.     

Power measurement setup for large signal microwave characterization at 94 GHz

We report the development of a power measurement setup in order to characterize devices at 94GHz. A very careful calibration of the setup has been performed in order to take into account in a most accurate way the losses through the different parts of the bench and in particular through the tuner. These aware power measurements have allowed to demonstrate state of the art power results on two different devices. We reached at 94GHz an output power of 876mW/mm associated to a 7.5-dB power gain and a power added efficiency (PAE) of 33% on a pseudomorphic high electron mobility transistor (PHEMT) on GaAs substrate. We achieved a 260-mW/mm maximum output power density with 5.9-dB power gain and 11% PAE on an InAsP channel HEMT on InP substrate.     

Ultrathin barrier GaN-on-Silicon devices for millimeter wave applications

In this paper, the possibility to use GaN-on-Silicon devices for millimeter wave applications by means of ultrathin barrier layers is reviewed. In particular, an emerging double heterostructure high electron mobility transistor (DHFET) based on AlN/GaN/AlGaN grown on silicon substrate is described, which enables a unique simultaneous achievement of high breakdown voltage and high frequency performance. This configuration system allowed for state-of-the-art GaN-on-Silicon DC, RF output power and noise performances at 40 GHz, paving the way for high performance mmW cost-effective amplifiers. Preliminary reliability assessment has been performed for the first time on this new class of RF devices, showing promising device stability.     

Enhancing the sustainability and energy conservation in heritage buildings: The case of Nottingham Playhouse

Today, there is a growing interest in developing energy efficient buildings since it is estimated that buildings account for about 40% of the total primary energy consumption in the world. In relation to existing buildings, energy efficiency retrofits have become an important opportunity to upgrade the energy performance of commercial, public and residential buildings that may reduce the energy consumption, demand and cost. In this paper we cover the energy efficiency deep retrofit process that has been carried out for Nottingham Playhouse theatre building for the aim of enhancing its environmental performance and analysing the energy efficiency gained after implementing certain proposed modifications. It is a nationally protected historic building, listed as Grade II1 on The National Heritage List for England (NHLE). The building has had insulation enhancement, doors modifications, solar energy installations, energy-saving lights, in addition to improved heating and air conditioning system. The paper presents a novel methodology; and its results indicate significant improvements in the building's energy performance which is demonstrated using infrared thermographic images and data logger sensors where significant energy savings to the building's thermal performance are obtained. The energy saving measures have been completed while maintaining the heritage building's general appearance and architectural features, which have received a Commendation Certificate from The Nottingham Civic Society for this achievement.     

Barrier-Layer Scaling of InAlN/GaN HEMTs

We discuss the characteristics of high-electron mobility transistors with barrier thicknesses between 33 and 3 nm, which are grown on sapphire substrates by metal-organic chemical vapor deposition. The maximum drain current (at V_G = 2.0 V) decreased with decreasing barrier thickness due to the gate forward drive limitation and residual surface-depletion effect. Full pinchoff and low leakage are observed. Even with 3-nm ultrathin barrier, the heterostructure and contacts are thermally highly stable (up to 1000degC).     

Combining diamond electrodes with GaN heterostructures for harsh environment ISFETs

Electrochemistry and biochemistry have always been ideal applications for diamond due to its chemical inertness and stability, sensitivity and biocompatibility. Several diamond ChemFET concepts have been proposed to date, however further improvements are still needed to obtain functional devices that can be operated efficiently beyond the reach of the well established silicon ISFET technology [P. Bergveld, Sensor and Actuators B, Chem. 88 (2003), pp. 1].In this paper we describe a novel ISFET structure in which a boron doped diamond electrochemical gate electrode is combined and monolithically integrated with an InAlN/GaN HEMT structure. The new device merges the high chemical stability of diamond with the high transconductance and low pinch-off voltage of InAlN/GaN heterostructure FETs, resulting in a highly stable ISFET with high sensitivity. First devices have been fabricated and electrochemically characterized, expressing high current levels, a pH sensitivity of about 50 mV/pH, complete current modulation when operated within the electrochemical window of the electrode in the range of pH 1 to pH 13 and high stability upon pH cycling and the application of high anodic overpotentials.     

Low On-Resistance High-Breakdown Normally Off AlN/GaN/AlGaN DHFET on Si Substrate

Ultrathin-barrier normally off AlN/GaN/AlGaN double-heterostructure field-effect transistors using an in situ SiN cap layer have been fabricated on 100-mm Si substrates for the first time. The high 2DEG density in combination with an extremely thin barrier layer leads to enhancement-mode devices with state-of-the-art combination of specific on-resistance that is as low as 1.25 $hbox{m}Omegacdothbox{cm}^{2}$ and breakdown voltage of 580 V at ${V}_{rm GS} = hbox{0} hbox{V}$ . Despite the 2-$muhbox{m}$ gate length used, the transconductance peaks above 300 mS/mm. Furthermore, pulsed measurements show that the devices are dispersion free up to high drain voltage ${V}_{rm DS} = hbox{50} hbox{V}$. More than 200 devices have been characterized in order to confirm the reproducibility of the results.      

InP HEMT downscaling for power applications at W band

We have developed new solutions for InP high-electron mobility transistor (HEMT) scaling for power applications at W band. We have shown that the use of a small barrier thickness in order to respect the aspect ratio for a 70-nm gate length results in a significant kink effect and high gate source capacitances. We have also shown through a theoretical study that a structure containing an InP layer between the cap layer and the barrier would support both the frequency performances and the breakdown voltage. Thus, we propose an HEMT structure containing a thick InP/AlInAs composite barrier and where the gate is buried into the barrier. This enables us to respect the aspect ratio and simultaneously to obtain an important drain current density without observing any kink effect. Moreover, we have applied this process to structures containing innovative large band-gap InP and InAsP channels. We have achieved the best frequency performances ever reached for an InP channel HEMT structure. Power measurements at 94 GHz were performed on these devices. The InAsP channel HEMT demonstrated a maximum output power of 260 mW/mm at 3 V of drain voltage with 5.9-dB power gain and a power-added efficiency of 11%. These results are favorably comparable to the state-of-the-art of InP-based HEMT at this frequency.     

Inductively coupled plasma — plasma enhanced chemical vapor deposition silicon nitride for passivation of InP based high electron mobility transistors (HEMTs)

Silicon nitride thin films have been deposited on InP-based structures at both room and high temperatures in an RF-inductively coupled plasma enhanced chemical vapor deposition (ICP-PECVD) equipment. Metal insulating semiconductor (MIS) diodes have been widely investigated using either SiH₄+NH₃ or SiH₄+N₂ gas phase. I–V measurements conducted on these diodes reveal high resistivity and breakdown electric field even at low deposition temperature (50°C). Double channel (DC) High electron mobility transistors (HEMTs) have been passivated by SiN_x films deposited at room temperature using SiH₄+NH₃ precursors. Passivated devices exhibit a very low drift over a 45 h period of stress under high gate-drain electric field.