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Hot-electron temperature (T-e) in InAlN/GaN high-electron-mobility transistors (HEMTs) was determined using electroluminescence spectroscopy as a function of gate voltage and correlated with the Te distribution determined by hydrodynamic simulations. Good agreement between measurement and simulations suggests that hot electrons can locally reach temperatures of up to 30 000 K at V-ds = 30 V, i.e., two to three times higher than that typically obtained for similar AlGaN/GaN HEMTs. The consequence of such high Te in InAlN/GaN HEMTs is illustrated by electrical stressing in OFF and semi-ON state at V-gd = 100 V. Prominent channel degradation was observed for devices stressed in semi-ON state, suggesting hot-electron driven degradation. Threshold voltage and drain current transient analyses indicate that hot electrons increase the density of traps in the GaN channel underneath the gate as well as surface/interface traps located in the gate-to-drain access region.

We report on preparation and electrical characterization of InAlN/AlN/GaN metal–oxide–semiconductor high electron mobility transistors (MOS HEMTs) with Al2O3 gate insulation and surface passivation. About 12 nm thin high-κ dielectric film was deposited by MOCVD. Before and after the dielectric deposition, the samples were treated by different processing steps. We monitored and analyzed the steps by sequential device testing. It was found that both intentional (ex situ) and unintentional (in situ before Al2O3 growth) InAlN surface oxidation increases the channel sheet resistance and causes a current collapse. Post deposition annealing decreases the sheet resistance of the MOS HEMT devices and effectively suppresses the current collapse. Transistors dimensions were source-to-drain distance 8 μm and gate width 2 μm. A maximum transconductance of 110 mS/mm, a drain current of ∼0.6 A/mm (VGS = 1 V) and a gate leakage current reduction from 4 to 6 orders of magnitude compared to Schottky barrier (SB) HEMTs was achieved for MOS HEMT with 1 h annealing at 700 °C in forming gas ambient. Moreover, InAlN/GaN MOS HEMTs with deposited Al2O3 dielectric film were found highly thermally stable by resisting 5 h 700 °C annealing.

In this article, we optimized the ohmic contact processing in InAlN/GaN high electron mobility transistors for the lower temperature of annealing by recessing of metalliza-tion to approach the 2DEG at the InAlN/GaN interface. The ohmic contacts which were recessed down to 5 nm depth and annealed at 700 °C 2 min. exhibited the contact resistance of 0,39 Ωmm while the channel sheet resistance was 210 Ω/square. These values are comparative to values of contacts processed at more conventional an-nealing conditions (800 °C, 2 min). Moreover we applied the recessed ohmic contact technology to fabricate Schottky barrier (SB) HEMTs and MOSHEMTs with Al2O3 dielectric film. For MOSHEMTs, we measured the maximal reduction of the gate leakage current by about 6 orders of magnitude if compared with SB HEMTs. The maximal drain current of MOSHEMTs was about 750 mA/mm at VGS = 0 V and the maximal extrinsic transconductance (gme) reached 101 mS/mm. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

AlGaN/GaN metal?oxide?semiconductor heterostructure field-effect transistors (MOSHFETs) with 4 nm thick Al2O3 gate oxide were prepared and their performance was compared with that of AlGaN/GaN HFETs. The MOSHFETs yielded ~40% increase of the saturation drain current compared with the HFETs, which is larger than expected due to the gate oxide passivation. Despite a larger gate-channel separation in the MOSHFETs, a higher extrinsic transconductance than that of the HFETs was measured. The drift mobility of the MOSHFETs, evaluated on large-gate FET structures, was significantly higher than that of the HFETs. The zero-bias mobility for MOSHFETs and HFETs was 1950 cm2 V?1 s?1 and 1630 cm2 V?1 s?1, respectively. These features indicate an increase of the drift velocity and/or a decrease of the parasitic series resistance in the MOSHFETs. The current collapse, evaluated from pulsed I?V measurements, was highly suppressed in the MOSHFETs with 4 nm thick Al2O3 gate oxide. This result, together with the suppressed frequency dispersion of the capacitance, indicates that the density of traps in the Al2O3/AlGaN/GaN MOSHFETs was significantly reduced.

We report on AlGaN/GaN metal-oxide-semiconductor heterostructure field-effect transistors (MOSHFETs) with MOCVD deposited Al2O3 as a gate oxide. Properties of MOSHFETs with 9 nm and 14 nm thick Al2O3 are compared with conventional HFETs prepared simultaneously on the same layer structure. Lower gate leakage current (∼10–5 A/mm at –10 V) and higher saturated drain current (up to 40%) are obtained for MOSHFETs than those for HFETs. In contradiction to previously reported data, the extrinsic transconductance for MOSHFETs is also higher (up to 37% of peak values) than that for HFET. This indicates on semi-conductive rather than insulating properties of Al2O3 gate oxide. Pulsed I–V measurements (pulse width 1 µs) yielded lower but still measurable current collapse in MOSHFETs compared to HFETs. Nevertheless, obtained results show that Al2O3 gate oxide, after optimising its microstructure and thickness, can be preferable for the preparation of AlGaN/GaN MOSHFETs. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We investigate electrical properties of Ni/Al2O3/GaN metal–oxide–semiconductor (MOS) structures having different pre-treatment of GaN surface by O2, Ar and NH3, combined with various temperature of annealing. MOS and reference Ni/GaN Schottky contact are characterized using current–voltage and capacitance–voltage methods. MOS structures compared with the Schottky contact ones show leakage current reduction for all types of processing, from 3 to 5 orders of magnitude in reverse direct. We observed substantial influence of the pre-treatment on electrical parameters of MOS structures.

We have prepared rare earth oxides based MOSFET gate stacks using metal-organic chemical vapour deposition, MOCVD. Gd2O3, La2O3, Nd2O3 and Pr6O11 films with thickness 3–20 nm were deposited on silicon substrate at 500 °C. The films were characterized by X-ray diffraction, X-ray reflectivity, transmission electron microscopy and X-ray photoelectron spectroscopy. As a next step, Ru films were grown on the dielectric films at 300 °C as a gate electrode. Electrical characterization of the MOS structures was performed by capacitance–voltage measurements. The structures annealed at 430 °C in forming gas (90% N2+10% H2) exhibited dielectric constant ranging from 12 to 14. Typically, the films showed high values of fixed oxide charge density, N ox ∼ 1 0 12 cm - 2 . Fixed oxide charges can be decreased by post-deposition annealing in forming gas and in oxygen.

A Schottky-barrier normally off InAlN-based high-electron-mobility transistor (HEMT) with selectively etched access regions, high off-state breakdown, and low gate leakage is presented. Metal-organic chemical vapor deposition-grown 1-nm InAlN/1-nm AlN barrier stack is capped with a 2-nm-thick undoped GaN creating a negative polarization charge at a GaN/InAlN heterojunction. Consequently, the gate effective barrier height is increased, and the gate leakage as well as the equilibrium carrier concentration in the channel is decreased. After removal of the GaN cap at access regions by using a highly selective dry process, the extrinsic channel becomes populated by carriers. Normally off HEMTs with 8-μm source-to-drain distance and 1.8-μm -long symmetrically placed gate showed a source drain current of about 140 mA/mm. The HEMT gate leakage at a drain voltage of 200 V and grounded gate is below 10-7 A/mm with a three-terminal device breakdown of 255 V. The passivated InAlN surface potential has been calculated to be 1.45 V; significant drain current increase is predicted for even lower potential.

The gate leakage reduction about four to seven orders of magnitude for HfO 2 MOSHFETs (~10−10A/mm at −15V) prepared by Atomic Layer Deposition (ALD) technique at 350°C with and without oxygen-plasma treatment in comparison to HFET, was observed. A lower hysteresis evaluated from c-V curves of MOSHFET with oxygen-plasma treatment (OPT) after annealing (500°C for 15 min in N 2 ) was found. The C-V curve for MOSHFET without OPT exhibited an increase of capacitance at negative voltages which corresponds with hypothesis of the interfacial layer formation at the oxide/GaN interface. And also, the high density of oxide interface states affects adversely the interface quality, like as the C-V hysteresis, leakage current, hot electron phenomena, etc.

We present GaN-based high electron mobility transistors (HEMTs) with a 2-nm-thin InAlN/AlN barrier capped with highly doped n(++) GaN. Selective etching of the cap layer results in a well-controllable ultrathin barrier enhancement-mode device with a threshold voltage of +0.7 V. The n(++) GaN layer provides a 290-Omega/square sheet resistance in the HEMT access region and eliminates current dispersion measured by pulsed IV without requiring additional surface passivation. Devices with a gate length of 0.5-mu m exhibit maximum drain current of 800 mA/mm, maximum transconductance of 400 mS/mm, and current cutoff frequency f(T) of 33.7 GHz. In addition, we demonstrate depletion-mode devices on the same wafer, opening up perspectives for reproducible high-performance InAlN-based digital integrated circuits.

We investigate InAlN/AlN/GaN-based MOS-HEMTs with and without a 20 A-GaN capping below an Al2O3-insulator. An excellent reduction of the leakage current, up-to 6 orders of magnitude, is observed in MOS-HEMT structures compared to Schottky-based-HEMTs, both with GaN capping. In the case of uncapped samples the reduction in the leakage current is 3 orders of magnitude. The maximal transconductance value gm,max for the GaN-capped-MOS-HEMT is about 10% higher than that for the conventional Schottky-based-HEMT, while in the case of uncapped devices gm,max is about the same for both Schottky and MOS-HEMT. Similarly the maximal-drain-current in the GaN capped MOS-HEMT is 950mA/mm, exhibiting an increase of 180mA/mm in comparison to the corresponding conventional Schottky-based-HEMT. Performance improvement of MOS structure can be explained by a mobility-dependent carrier depletion effect. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Early stage degradation of InAlN/GaN HEMTs submitted to OFF and semi-ON state stress at a drain bias of 50 V was investigated. Degradation in different parts of the device upon OFF and semi-ON state stress inferred from the comprehensive electrical characterization indicates predominantly an hot-electron degradation mechanism, as no degradation in the gate leakage current was observed for both stress conditions. Based on ‘end’ resistance measurements suggesting more pronounced degradation in the drain and source resistance after OFF and semi-ON state stressing, respectively, it is speculated that impact ionization can play a role in the degradation of InAlN/GaN HEMTs.

Application of GaAs-based metal-oxide-semiconductor (MOS) structures, as a "high carrier mobility" alternative to conventional Si MOS transistors, is still hindered due to difficulties in their preparation with low surface/interface defect states. Here, aluminum oxide as a passivation and gate insulator was formed by room temperature oxidation of a thin Al layer prepared in situ by metal-organic chemical vapor deposition. The GaAs-based MOS structures yielded two-times higher sheet charge density and saturation drain current, i.e., up to 4 x 10 12 cm(-2) and 480 mA/mm, respectively, than the counterparts without an oxide surface layer. The highest electron mobility in transistor channel was found to be 6050 cm(2)/V s. Capacitance measurements, performed in the range from 1 kHz to 1 MHz, showed their negligible frequency dispersion. All these results indicate an efficient suppression of the defect states by in situ preparation of the semiconductor structure and aluminum oxide used as a passivation and gate insulator. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3701584]

We present electrical characterization of Si(p)/GdScO 3 /Ru metal-oxide-semiconductor structures prepared by liquid injection metal organic chemical vapour deposition. Capacitance-voltage measurement revealed dielectric constant κ=22. Density of interface states was determined using conductance measurement. Annealing in forming gas resulted in decrease of the interface state density in the middle of the Si band-gap to 5 * 1011 eV−1cm−2.

Design considerations and performance of n(++) GaN/InAlN/AlN/GaN normally off high-electron mobility transistors (HEMTs) are analyzed. Selective and damage-free dry etching of the gate recess through the GaN cap down to a 1-nm-thick InAlN barrier secures positive threshold voltage, while the thickness and the doping of the GaN cap influence the HEMT direct current and microwave performance. The cap doping density was suggested to be 2 x 10(20) cm(-3). To screen the channel from the surface traps, the needed cap thickness was estimated to be only 6 nm. Design is proved by an experiment showing a constant value of the HEMT dynamical access resistance, while a single-pulse experiment indicated almost collapse-free performance. On the other hand, it is found that the n(++) GaN cap does not contribute to the HEMT drain current conduction, nor does it provide a path for the OFF-state breakdown. HEMTs with a gate length of 0.25 mu m and a 4-mu m source-to-drain distance show a drain-to-source current of 0.8 A/mm, a transconductance of 440 mS/mm, a threshold voltage of similar to 0.4 V, and a cutoff frequency of 50 GHz. A thin and highly doped GaN cap is also found to be suitable for the processing of normally on HEMTs by adopting the nonrecessed gate separated from the cap by insulation.

We present analysis of thermal stability of thin GdScO3 films grown on silicon and InAlN/GaN substrates. The GdScO3 films were prepared by liquid injection metal organic chemical vapor deposition at 600 °C. The films were processed after deposition by rapid thermal annealing in nitrogen ambient at 900, 1000 and 1100 °C during 10 s. In addition, annealing of the GdScO3 films on InAlN/GaN substrate at 700 °C during 3 hours was performed. The samples were analyzed by grazing incidence X-ray diffraction (GIXRD), X-ray reflectivity (XRR) and time-of-flight secondary ion mass spectroscopy (ToF SIMS). GIXRD confirmed that the as-deposited GdScO3 films were amorphous. Recrystallization of the films on both substrates occurred at 1100 °C. ToF SIMS depth profile of the films annealed at 1000 °C indicated strong reaction of the GdScO3 film with the Si substrate. For the InAlN/GaN substrate rapid thermal annealing at 900 °C induced diffusion of the In and Al atoms into the top GdScO3 layer. Thermal treatment at 700 °C for 3 hours presents upper limit of the acceptable thermal budget for the GdScO3/InAlN interface.

In this article, we investigate the effect of a rapid thermal annealing (RTA) on electrical properties InAIN/GaN MOSHEMT with Al2O3 insulating film. On samples, we measured input, output and pulse characteristics. Consequently, a threshold voltage and an extrinsic transconductance was determined. A more dramatic influence of RTA was observed after annealing at 700degC. In this case, a reduction of the leakage current was about 7 orders of magnitude compared with HEMT structures without the insulating film.

The authors have prepared μm-sized HfO2-based nonplanar resistive switching cells with TiN and Pt electrodes. The structures exhibited stable resistive switching loops with low resistance state current below 1 mA. The influence of series resistance of the TiN strip electrode on the switching characteristics was measured and simulated. It was shown that the series resistance reduces the low state resistance current as well as high to low resistance state ratio.

The I-V and C-V measurements were used for characterization of AlGaN/GaN HFETs and MOSHFETs. Deposited Al2O31 gate oxide yielded an increase of the sheet carrier density from 6.9times 1012 to 7.25 times 1O12 cm-2 and subsequent increase of the drain current density up to 40% and increase of the extrinsic transconductance up to 37%, respectively. The gate leakage current of 10-5 A/mm at -10 V is about 3 orders of magnitude lower than that of HFETs. This results indicate the suitability of a thick Al2O3 gate oxide for improvement of electronic properties of GaN-based MOSHFETs

In this paper we investigate growth of Al2O3 and performance of Al2O3/GaN MOS structures using O2, Ar and NH3 pre-treatment of GaN surface. Rapid thermal annealing (RTA) after the growth is also tested. Current-voltage (I-V) and thermal activation energy measurements were used for characterization of MOS and reference Ni/GaN Schottky contact structures. From the I-V characteristics, reduction of the leakage current was observed in MOS structures compared with the Schottky contacts for all types of processing, from three to five orders of magnitude in the reverse bias. Barrier height at the semiconductor-insulator interface (PhiS-1), which is responsible for the reduction of the forward bias leakage was extracted from the thermal I-V measurements. Values of PhiS-1 was found to be ~1.6eV for O2 and ~2.5eV for Ar treated samples and these samples show substantial leakage reduction in both senses. On the other hand I-V performance of the MOS structures with the NH3 pretreatment resemble Schottky contact diode-like characteristic

In this paper, thermal stability o/metal-organics vapour deposited (MOCVD) Ru gate electrodes grown on atomic-layer deposited (ALD) Hf02 dielectric films have been analysed. As-deposited MOS capacitors were annealed in forming gas (10% H2 + 90% N2) at temperature range 430 - 590 °C for 30 min. MOS capacitors were analysed by high-frequency capacitance-voltage (G-V), conductance-voltage (G-V) and current voltage (I-V) measurements resulting density of oxide charge, Neff, density of interface states, Dii and leakage current density, Jleak respectively.

The authors report on preparation and electrical characterization of InAlN/AlN/GaN metal-oxide-semiconductor (MOS) high electron mobility transistors (HEMTs) with Al2O3, ZrO2, and GdScO3 gate dielectrics. About 10 nm thick high-κ dielectrics were deposited by metal organic chemical vapor deposition after the Ohmic contact processing. Application of the gate dielectrics for 2 μm gate length MOS HEMTs leads to gate leakage current reduction from four to six orders of magnitude compared with Schottky barrier HEMTs. Among others, MOS HEMTs with an Al2O3 gate dielectric shows the highest transconductance (∼150 mS/mm) and maximum drain current (∼0.77 A/mm) and the lowest sheet resistance of ∼260 Ω/◻. MOS HEMTs with GdScO3 shows the highest breakdown electric field of about 7.0 MV/cm. A deep level transient spectroscopy (DLTS) based analysis revealed the maximum interface state density Dit up to 4×1012, 9×1012, and 3×1013 eV−1 cm−2 for Al2O3, ZrO2, and GdScO3/InAlN interface, respectively.

We investigate Al2O3- and ZrO2/InAlN/GaN metal-oxide-semiconductor heterostructures (MOS-H) using capacitance-time transients in the temperature range of 25-300 degrees C. A deep-level transient spectroscopy based analysis revealed the maximum interface state density distributions D-it(E) up to 3 x 10(13) and 1 X 10(13) eV(-1) cm(-2) for the Al2O3/InAlN and ZrO2/InAlN interface, respectively. The integral densities of interface states correlate well with the trapping-related gate-lag effect in corresponding InAlN/GaN MOS high electron mobility transistors (HEMTs). This explains the strongly reduced lag effect in ZrO2 MOS HEMTs. We assume hole trapping at oxide/InAlN interface to be a dominant effect responsible for the gate-lag effect in InAlN/GaN MOS HEMTs. (C) 2009 The Japan Society of Applied Physics 10.1143/JJAP.48.090201

We describe preparation and properties of GdScO3 thin films. The films were prepared by liquid injection metal-organic chemical vapor deposition, MOCVD at 600 ºC on (100) Si substrate. The as-deposited films were amorphous with a smooth surface and sharp GdScO3/Si interface. X-ray diffraction showed that the amorphous phase is well preserved upon rapid thermal annealing up to 1000 ºC. However, modification of the X-ray reflectivity pattern after annealing at 1000 ºC indicates increasing of the film thickness, presumably due to diffusion of silicon from the substrate into the whole volume of the film. Capacitance-voltage measurement resulted in dielectric constant of 22. It is shown, that exact stoichiometry of GdScO3 is not necessary to achieve dielectric constant above 20.

Al2O3 thin films were deposited by a metal organic chemical vapour deposition on InAlN∕GaN heterostructures using Ar or NH3 as a carrier gas. Effects of NH3 and Ar carrier gases on the electrical and structural properties of Al2O3∕InAlN∕GaN HEMT devices were investigated by current voltage, current collapse, and Auger electron spectroscopy measurements. Al2O3 deposited using Ar as a carrier gas leads to a substantial gate leakage current reduction with no increase of the current collapse compare to Schottky gate based HEMT. On the other hand, HEMT electrical performance shows degradation if NH3 carrier gas is used. Similarly, Auger electron spectroscopy revealed presence of carbon on InAlN surface when NH3 carrier gas was applied. It is suggested that the formation of carbon-related traps on the InAlN surface takes place in the early stages of the Al2O3 deposition with NH3 carrier gas that strongly influences the HEMT performance.

The authors report on improved transport properties of Al2O3∕AlGaN∕GaN metal-oxide-semiconductor heterostructure field-effect transistors (MOSHFETs). It is found that the drift mobility in the MOSHFET structures with 4nm thick Al2O3 gate oxide is significantly higher than that in HFETs. The zero-bias mobilities are 1950 and 1630cm2∕Vs for the MOSHFET and HFET, respectively. An ∼40% increase of the saturation drain current in the MOSHFETs compared to the HFETs seems to be larger than expected from the passivation effects. The MOSHFET devices show a higher transconductance (with peak values of ∼115mS∕mm) than the HFETs (∼70mS∕mm). Analysis of the device performance indicates a decrease of the parasitic series resistance together with an enhancement of the effective velocity of the channel electrons in the MOSHFET devices.

Capacitance-voltage characteristics of Ru/Hf x Si 1-x O y /Si gate stacks with Hf x Si 1-x O y composition Hf/Si = 75/25 and Hf/Si = 50/50 were analyzed. The characteristics revealed a high density of negative fixed charges N ox as -5 X 10 12 cm -2 in the oxide film. We have observed that the value of the Ru work function remained constant after forming gas annealing at temperatures between 430 and 510°C, respectively, while fixed charges were reduced at temperatures above 470°C. We speculated that the decrease of negative fixed charges can be explained by the generation of positively charged [Si 2 = OH] + centers in the oxide layer. The positively charged centers can account for a compensation of the negative fixed oxide charge. Rapid thermal annealing at temperatures up to 800°C in nitrogen did not influence the fixed oxide charges in the Hf x Si i-x O y films.

InAlN/GaN is indeed an alternative to the common AlGaN/GaN heterostructure in electronics and sensing. It enables operation at extremely high temperature once problems with contact metallization and passivation have been solved. It is the only heterostructure known presently, which allows overgrowth of high quality diamond films to combine two of the most stable semiconductors. Thus, applications reach from high power microwaves systems and high temperature electronics to sensing in harsh environment.

The authors investigate 2 mu m gate-length InAlN/GaN metal-oxide-semiconductor high-electron-mobility transistors (MOS HEMTs) with 12 nm thick Al2O3 gate insulation. Compared to the Schottky barrier (SB) HEMT with similar design, the MOS HEMT exhibits a gate leakage reduction by six to ten orders of magnitude. A maximal drain current density (I-DS=0.9 A/mm) and an extrinsic transconductance (g(me)=115 mS/mm) of the MOS HEMT also show improvements despite the threshold voltage shift. An analytical modeling shows that a higher mobility of electrons in the channel of the MOS HEMT and consequently a higher number of electrons attaining the velocity saturation may explain the observed increase in g(me) after the gate insulation. (C) 2007 American Institute of Physics.