A novel “in-situ” processed gate region on GaN MOS capacitors

This work reports a route to the realisation of GaN metal oxide semiconductor capacitors (MOSCAPs) where the GaN surface has not been exposed to atmosphere. This has been achieved by the deposition of a 5nm SiNx “capping” layer as the final part of the GaN on Si MOSCAP wafer growth to encapsulate the GaN surface, followed by its removal in a “cluster” plasma processing tool, which enables both etching of samples and subsequent dielectric and metal deposition without atmospheric exposure between process steps. Capacitance-voltage hysteresis, A Hysteresis, of 90mV and frequency dispersion, A dispersion, of 150mV were achieved from samples where the SiNx capping layer was etched and then transferred under vacuum prior to atomic layer deposition (ALD) of a 20 nm Al2O3 gate dielectric. These were lower than the previously reported values of 250mV and 350mV respectively for GaN-Al2O3 MOS capacitors where the GaN surface had been exposed to atmosphere. The effects of N2 and H2 plasma treatments after SiNx etch and prior to Al2O3 deposition were examined. Exposure to a 150W N2 plasma for 5 minutes produced a Hysteresis and a Dispersion of 200mV and 250mV respectively, both of which reduced to 60mVafter forming gas annealing (FGA) in 10% H2/90% N2 for 30 minutes at 430oC. The insertion of an ALD grown AlN interlayer between an air exposed GaN surface and the Al2O3 gate dielectric resulted in 50mV a Hysteresis and a Dispersion. However, when the process was transferred to samples that went through the SiNx etch and optimised N2 plasma pretreatment, both a Hysteresis and a Dispersion increased to 500mV. The effect of ALD deposition of a TiN gate metal after Al2O3 gate dielectric was also examined. SiNx capped samples were first etched in the cluster tool before transfer to the ALD chamber in which a 20nm Al2O3 gate dielectric was deposited. This was followed by atomic layer deposition of 20nm TiN gate metal. a Hysteresis and a Dispersion of 550mV and 400mV respectively were obtained. These samples had a capacitance-voltage slope which was 155% higher than otherwise comparable structures with Pt/Au gate metal. In conclusion the reductions in a Hysteresis and a Dispersion achieved in this work during in-situ etching and ALD are encouraging for the realisation of high power GaN devices

Optical properties of refractory metal based thin films

There is a growing interest in refractory metal thin films for a range of emerging nanophotonic applications including high temperature plasmonic structures and infrared superconducting single photon detectors. We present a detailed comparison of optical properties for key representative materials in this class (NbN, NbTiN, TiN and MoSi) with texture varying from crystalline to amorphous. NbN, NbTiN and MoSi have been grown in an ultra-high vacuum sputter deposition system. Two different techniques (sputtering and atomic layer deposition) have been employed to deposit TiN. We have carried out variable angle ellipsometric measurements of optical properties from ultraviolet to mid infrared wavelengths. We compare with high resolution transmission electron microscopy analysis of microstructure. Sputter deposited TiN and MoSi have shown the highest optical absorption in the infrared wavelengths relative to NbN, NbTiN or ALD deposited TiN. We have also modelled the performance of a semi-infinite metal air interface as a plasmonic structure with the above mentioned refractory metal based thin films as the plasmonic components. This study has implications in the design of next generation superconducting nanowire single photon detector or plasmonic nanostructure based devices

Design and characterisation of titanium nitride sub-arrays of kinetic inductance detectors for passive terahertz imaging

We report on the investigation of titanium nitride (TiN) thin films deposited via atomic layer deposition (ALD) for microwave kinetic inductance detectors (MKID). Using our in-house ALD process, we have grown a sequence of TiN thin films (thickness 15, 30, 60 nm). The films have been characterised in terms of superconducting transition temperature Tc , sheet resistance Rs and microstructure. We have fabricated test resonator structures and characterised them at a temperature of 300 mK. At 350 GHz, we report an optical noise equivalent power NEPopt≈2.3×10−15 W/√Hz , which is promising for passive terahertz imaging applications

Dual barrier InAlN/AlGaN/GaN-on-silicon high-electron-mobility transistors with Pt and Ni based gate stacks

In this work, we report the performance of 3 μm gate length "dual barrier„ InAlN/AlGaN/GaN HEMTs on Si substrates with gate-drain contact separations in the range 4-26 μm. Devices with Pt and Ni based gates were studied and their leakage characteristics are compared. Maximum drain current IDS of 1 A/mm, maximum extrinsic transconductance gm ~203 mS/mm and on-resistance Ron 4.07 Ω mm for gate to drain distance LGD = 4 μm were achieved. Nearly ideal sub-threshold swing of 65.6 mV/dec was obtained for LGD = 14 μm. The use of Pt based gate metal stacks led to a two to three orders of magnitude gate leakage current decrease compared to Ni based gates. The influence of InAlN layer thickness on the transistor transfer characteristics is also discussed

Innovative remote plasma source for atomic layer deposition for GaN devices

High-quality dielectric films could enable GaN normally off high-electron-mobility transistors (HEMTs). Plasma atomic layer deposition (ALD) is known to allow for controlled high-quality thin-film deposition, and in order to not exceed energy and flux levels leading to device damage, the plasma used should preferably be remote for many applications. This article outlines ion energy flux distribution functions and flux levels for a new remote plasma ALD system, Oxford Instruments Atomfab™, which includes an innovative, RF-driven, remote plasma source. The source design is optimized for ALD for GaN HEMTs for substrates up to 200 mm in diameter and allows for Al2O3 ALD cycles of less than 1 s. Modest ion energies of <50 eV and very low ion flux levels of <1013 cm−2 s−1 were found at low-damage conditions. The ion flux can be increased to the high 1014 cm−2 s−1 range if desired for other applications. Using low-damage conditions, fast ALD saturation behavior and good uniformity were demonstrated for Al2O3. For films of 20 nm thickness, a breakdown voltage value of 8.9 MV/cm was obtained and the Al2O3 films were demonstrated to be suitable for GaN HEMT devices where the combination with plasma pretreatment and postdeposition anneals resulted in the best device parameters

The 2018 GaN power electronics roadmap

Gallium nitride (GaN) is a compound semiconductor that has tremendous potential to facilitate economic growth in a semiconductor industry that is silicon-based and currently faced with diminishing returns of performance versus cost of investment. At a material level, its high electric field strength and electron mobility have already shown tremendous potential for high frequency communications and photonic applications. Advances in growth on commercially viable large area substrates are now at the point where power conversion applications of GaN are at the cusp of commercialisation. The future for building on the work described here in ways driven by specific challenges emerging from entirely new markets and applications is very exciting. This collection of GaN technology developments is therefore not itself a road map but a valuable collection of global state-of-the-art GaN research that will inform the next phase of the technology as market driven requirements evolve. First generation production devices are igniting large new markets and applications that can only be achieved using the advantages of higher speed, low specific resistivity and low saturation switching transistors. Major investments are being made by industrial companies in a wide variety of markets exploring the use of the technology in new circuit topologies, packaging solutions and system architectures that are required to achieve and optimise the system advantages offered by GaN transistors. It is this momentum that will drive priorities for the next stages of device research gathered here

Realisation of Low Annealing Temperature and Low Resistance Ohmic Contacts forAlGaN/GaN-Based Power Devices Via SiH4 Inductively Coupled Plasma Treatment

No abstract available

A Study of In-situ X-ray Photoelectron Spectroscopy Surface Analysis in Development of Atomic Layer Etch for GaN/AlGaN Based Power Device Fabrication

No abstract available

Realisation of Low Annealing Temperature and Low Resistance Ohmic Contacts forAlGaN/GaN-Based Power Devices Via SiH4 Inductively Coupled Plasma Treatment

No abstract available

Optical properties of refractory metal based thin films

There is a growing interest in refractory metal thin films for a range of emerging nanophotonic applications including high temperature plasmonic structures and infrared superconducting single photon detectors. We present a detailed comparison of optical properties for key representative materials in this class (NbN, NbTiN, TiN and MoSi) with texture varying from crystalline to amorphous. NbN, NbTiN and MoSi have been grown in an ultra-high vacuum sputter deposition system. Two different techniques (sputtering and atomic layer deposition) have been employed to deposit TiN. We have carried out variable angle ellipsometric measurements of optical properties from ultraviolet to mid infrared wavelengths. We compare with high resolution transmission electron microscopy analysis of microstructure. Sputter deposited TiN and MoSi have shown the highest optical absorption in the infrared wavelengths relative to NbN, NbTiN or ALD deposited TiN. We have also modelled the performance of a semi-infinite metal air interface as a plasmonic structure with the above mentioned refractory metal based thin films as the plasmonic components. This study has implications in the design of next generation superconducting nanowire single photon detector or plasmonic nanostructure based devices