Electron Mobility Transistors Research Articles

Improving Performance and Breakdown Voltage in Normally-Off GaN Recessed Gate MIS-HEMTs Using Atomic Layer Etching and Gate Field Plate for High-Power Device Applications.

A typical method for normally-off operation, the metal-insulator-semiconductor-high electron mobility transistor (MIS-HEMT) has been investigated. Among various approaches, gate recessed MIS-HEMT have demonstrated a high gate voltage sweep and low leakage current characteristics. Despite their high performance, obtaining low-damage techniques in gate recess processing has so far proven too challenging. In this letter, we demonstrate a high current density and high breakdown down voltage of a MIS-HEMT with a recessed gate by the low damage gate recessed etching of atomic layer etching (ALE) technology. After the remaining 3.7 nm of the AlGaN recessed gate was formed, the surface roughness (Ra of 0.40 nm) was almost the same as the surface without ALE (no etching) as measured by atomic force microscopy (AFM). Furthermore, the devices demonstrate state-of-the-art characteristics with a competitive maximum drain current of 608 mA/mm at a VG of 6 V and a threshold voltage of +2.0 V. The devices also show an on/off current ratio of 109 and an off-state hard breakdown voltage of 1190 V. The low damage of ALE technology was introduced into the MIS-HEMT with the recessed gate, which effectively reduced trapping states at the interface to obtain the low on-resistance (Ron) of 6.8 Ω·mm and high breakdown voltage performance.

Threshold Voltage Modulation Engineering Using p‐Type CuO and NiO for the AlGaN/GaN Enhancement‐Mode Fin‐MOS‐HEMTs on the Si Substrates

This work presents the threshold voltage modulation of the thin‐barrier Al0.45Ga0.55N/GaN Fin‐metal oxide semiconductor‐high electron mobility transistors (MOS‐HEMTs) with two types of p‐type metal oxide (CuO and NiO) and one type of HfO2 gate dielectrics. Different p‐type oxides and different fin structures can modulate the threshold voltage of the devices. The CuO and NiO Fin‐MOS‐HEMT with 60 nm fin width (W fin) achieves the V th value of 0.3 and 0.6 V, respectively. Compared with the conventional HEMT, the V th of NiO Fin‐MOS‐HEMT can be positively shifted by 2.5 V, validating the stronger 2D electron gas (2DEG) depletion by the p‐type oxide and the V th will shift forward with the decrease of W fin. Furthermore, the theoretical calculation model of Fin‐MOS‐HEMT threshold voltage is proposed, which is in good agreement with the experimental results. The proposed model can provide important guidelines for the AlGaN/GaN Fin‐MOS‐HEMTs development.

Influence of Interface trap distributions over the device characteristics of AlGaN/GaN/AlInN MOS‐HEMT using Cubic Spline Interpolation technique

AbstractTraps present at the interface of oxide and barrier layers influence the device's DC and RF parameters. An investigation is carried out on the distribution of interface traps present in the AlGaN/GaN/AlInN Metal Oxide Semiconductor‐High Electron Mobility Transistor (MOS‐HEMT) structures. By incorporating Hafnium Oxide (HfO2) as a dielectric layer, the DC and RF parameters like current drive and Power‐Added Efficiency (PAE) for the device are evaluated. The Capacitance‐Voltage (C–V) curves showed a shift in its values upon increase in trap density, which attributes to the position of fermi level once the threshold voltage is reached. A theoretical estimation of interface trap densities revealed distributions in the magnitude of 9.52 × 1012 cm−2 eV−1 near the mid‐gap and around 3.4 × 1013 cm−2 eV−1 at the Conduction Band (CB) edge. Carrier concentration at the Two‐Dimensional Electron Gas (2DEG) influences the distribution of traps at the interface, which in turn affects the on‐resistance of the device. Cubic Spline Interpolation (CSI) technique is employed here to model the device parameters precisely. The higk‐K dielectric material causes a high cut‐off of 201 GHz for the MOS‐HEMT. There is about 42% improvement in the PAE compared to the conventional MOS‐HEMT device. The comparably low trap density values (1012 cm−2 eV−1) than the conventional ones, prove the high quality gate passivation features of the HfO2/AlGaN interface and could serve as a potential candidate for high power and microwave applications.

New barrier layer design for the fabrication of gallium nitride-metal-insulator-semiconductor-high electron mobility transistor normally-off transistor

This paper reports on the fabrication of an enhancement-mode AlGaN/GaN metal-insulator-semiconductor-high electron mobility transistor with a new barrier epi-layer design based on double Al0.2Ga0.8N barrier layers separated by a thin GaN layer. Normally-off transistors are achieved with good performances by using digital etching (DE) process for the gate recess. The gate insulator is deposited using two technics: plasma enhance chemical vapour deposition (sample A) and atomic layer deposition (sample B). Indeed, the two devices present a threshold voltage (V th) of +0.4 V and +0.9 V respectively with ΔV th about 0.1 V and 0.05 V extracted from the hysteresis gate capacitance measurement, a gate leakage current below 2 × 10−10 A mm−1, an I ON/I OFF about 108 and a breakdown voltage of V BR = 150 V and 200 V respectively with 1.5 µm thick buffer layer. All these results are indicating a good barrier surface quality after the gate recess. The DE mechanism is based on chemical dissolution of oxides formed during the first step of DE. Consequently, the process is relatively soft with very low induced physical damages at the barrier layer surface.

Investigation of Structural, Optical and Electrical Properties of Al0.3Ga0.7N/GaN HEMT Grown by MOCVD

In this study, Al0.3Ga0.7N/GaN high electron mobility transistor (HEMT) structure is investigated grown over c- oriented sapphire substrate by using Metal Organic Chemical Vapor Deposition (MOCVD) method. Optical, morphological and electrical characteristics of this structure are determined by X-ray diffraction (XRD), Photoluminecanse (PL), Ultraviolet (UV-Vis.), Atomic Force Microscopy (AFM) and Hall- Resistivity measurements. By using XRD method, 2θ, Full Width at Half Maximun (FWHM), lattice parameters, crystallite size, strain, stress and dislocation values are calculated on symmetric and asymmetric planes. Direct band gap of GaN is determined by PL measurements as 3.24 eV. It is seen that conduction of AlGaN layer starts at 360 nm in UV-Vis. In Hall-Resistivity measurements, it is noticed that carrier density of HEMT structure is not effected by temperature and mobility value is high. Carrier density and mobility values are determined as 5.82x1015 1/cm3 and 1198 cm2/Vs at room temperature respectively. At the lowest temperature point (25 K) they are calculated as 5.19x1015 1/cm3 and 6579 cm2/Vs, respectively.

High-Performance Normally-OFF GaN MIS-HEMTs Using Hybrid Ferroelectric Charge Trap Gate Stack (FEG-HEMT) for Power Device Applications

A GaN metal-insulator-semiconductor-high electron mobility transistor (HEMT) using hybrid ferroelectric charge trap gate stack (FEG-HEMT) is demonstrated for normally-OFF operation. The ferroelectric (FE) polarization increases the number of trapped charges in the HfON charge trapping layer, leading to high positive threshold voltage (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> ) shift for the normally-OFF device. Besides, under the positive bias temperature instability (PBTI) test, the internal electric field induced by FE polarization causes smoother slope of the conduction band in FE gate stack, resulting in better V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> stability. With the proposed hybrid FE charge trap gate stack, the device exhibits a high V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> of +2.71 V at I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Dh</sub> = 1μA/mm, a high maximum current density of 820 mA/mm and low on-resistance (R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> ) of 11.1 Ω · mm. The FE device also shows good V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> -temperature stability compared to the non-FE device results. Besides, a high current device with 40 A is also fabricated in this letter to demonstrate the feasibility of the proposed FEG-HEMT device for high power device application.

Thermal Effects between Carbon-Doped GaN and AlGaN Back-Barrier in AlGaN/GaN HEMTs on Si (111) Substrates

Carbon-doped GaN and Al0.05Ga0.95N/Al0.08Ga0.92N back-barriers are employed as a semi-insulating buffer in AlGaN/GaN high- electron mobility transistor (HEMT) structures on Si (111). The AlGaN buffer exhibits improved breakdown behavior in high temperature operation owing to an additional potential barrier at the bottom of the GaN channel. The vertical and lateral leakage currents are reduced by 10X and 2X, respectively, resulting in 140 V higher reverse vertical breakdown, and 100 V higher lateral isolation breakdown voltage at 150°C. The AlGaN buffer shows slightly inferior room-temperature 2DEG transport properties as well as a roll-off in output characteristic suggesting a higher thermal impedance relative to the carbon-doped buffer. Both buffers are suitable for high-voltage operation, with the AlGaN showing advantageous leakage and breakdown properties at elevated temperature.

Deep trap-induced dynamic on-resistance degradation in GaN-on-Si power MISHEMTs

Identification and characterization of a single, deep trap causing large increases in the on-resistance of GaN-on-Si power metal-insulator-semiconductor-high electron mobility transistors (MISHEMTs) is reported. This is achieved by using HEMT-based deep level optical spectroscopy (DLOS) and related methods in conjunction with high voltage off-state VDS switching up to 400V. A trap with an activation energy of ~EC−2eV that is physically located in the drain-access region of the MISHEMT is shown to be the primary source of an increase of the dynamic on-resistance increase by as much as ~9 times at 400V operation. Comparisons of trap signatures extracted from the MISHEMT with capacitance-based DLOS measurements of simple Schottky-diode test-structures showing the same, dominant trap signature suggests that the physical defect is located within the GaN buffer and is not a surface or insulator-related defect. A buffer trap based model is presented to explain the observed on-resistance degradation effects in the MISHEMTs during high voltage switching.

Low-Temperature Scanning Capacitance Probe for Imaging Electron Motion

Novel techniques to probe electronic properties at the nanoscale can shed light on the physics of nanoscale devices. In particular, studying the scattering of electrons from edges and apertures at the nanoscale and imaging the electron profile in a quantum dot, have been of interest [1]. In this paper, we present the design and implementation of a cooled scanning capacitance probe that operates at liquid He temperatures to image electron waves in nanodevices. The conducting tip of a scanned probe microscope is held above the nanoscale structure, and an applied sample-to-tip voltage creates an image charge that is measured by a cooled charge amplifier [2] adjacent to the tip. The circuit is based on a low-capacitance, high- electron-mobility transistor (Fujitsu FHX35X). The input is a capacitance bridge formed by a low capacitance pinched-off HEMT transistor and tip-sample capacitance. We have achieved low noise level (0.13 e/VHz) and high spatial resolution (100 nm) for this technique, which promises to be a useful tool to study electronic behavior in nanoscale devices.

Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;/AlN/GaN MOS-Channel-HEMTs With an AlN Interfacial Layer

We report a high-performance normally-off Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /AlN/GaN MOS-channel-high electron mobility transistor (MOSC-HEMT) featuring a monocrystalline AlN interfacial layer inserted between the amorphous Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> gate dielectric and the GaN channel. The AlN interfacial layer effectively blocks oxygen from the GaN surface and prevents the formation of detrimental Ga-O bonds. Frequency-dispersion in <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</i> – <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> characteristics and threshold voltage hysteresis are effectively suppressed, owing to improved interface quality. The new MOSC-HEMTs exhibit a maximum drain current of 660 mA/mm, a field-effect mobility of 165 cm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">\(^{2}\) </tex-math></inline-formula> /V <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">\(\cdot \) </tex-math></inline-formula> s, a high on/off drain current ratio of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">\(\sim 10^{10}\) </tex-math></inline-formula> , and low dynamic on-resistance degradation.

RF and microwave characteristics of a 10 nm thick InGaN-channel gate recessed HEMT

A new depletion-mode gate recessed AlGaN/InGaN/GaN-high electron mobility transistor (HEMT) with 10 nm thickness of InGaN-channel is proposed. A growth of AlGaN over GaN leads to the formation of two-dimensional electron gas (2DEG) at the heterointerface. High 2DEG density (ns) is achieved at the heterointerface due to a strain induced piezoelectric effect between AlGaN and GaN layers. The electrons are confined in the InGaN-channel without spilling over into the buffer layer, which also reduces the buffer leakage current. From the input transfer characteristics the threshold voltage is obtained as −4.5 V and the device conducts a current of 2 A/mm at a drain voltage of 10 V. The device also shows a maximum output current density of 1.8 A/mm at Vds of 3 V. The microwave characteristics like transconductance, cut-off frequency, max frequency of oscillation and Mason's Unilateral Gain of the device are studied by AC small-signal analysis using a two-port network. The stability and power performance of the device are analyzed by the Smith chart and polar plots respectively. To our knowledge this proposed InGaN-channel HEMT structure is the first of its kind.

AlGaN/GaN-based HEMTs for electrical stimulation of neuronal cell cultures

Unipolar source–drain voltage pulses of GaN/AlGaN-high electron mobility transistors (HEMTs) were used for stimulation of cultured neuronal networks obtained from embryonic rat cerebral cortex. The HEMT sensor was grown by metal organic vapour phase epitaxy on a 2 inch sapphire substrate consisting of 10 single HEMTs concentrically arranged around the wafer centre. Electrolytic reactions between the HEMT sensor surface and the culture medium were not detected using cyclic voltammetry.During voltage pulses and resulting neuronal excitation, capacitances were recharged giving indications of the contributions of the AlGaN and AlOx isolation layers between the two-dimensional electron gas channel and the neuron culture. The resulting threshold current for stimulation of neuron activity strongly depended on the culture and HEMT position on the sensor surface under consideration which was caused by different impedances of each neuron culture and position within the culture. The differences of culture impedances could be explained by variations of composition, thickness and conductivity of the culture areas.

Broadband AlGaN/GaN MMIC amplifier

A broadband Monolithic Microwave Integrated Circuit (MMIC) amplifier, with 12 ± 2 dB gain across the 0.1–27 GHz band has been demonstrated using the AlGaN/GaN on SiC technology. The amplifier design employs a non-conventional, series-DC/RF-High Electron Mobility Transistor (HEMT) configuration. This configuration provides an alternative design to the conventional traveling-wave amplifier (TWA). It results in a smaller MMIC chip size, and extends amplifier gain to the low-frequency region. The amplifier MMIC utilizes four HEMT devices in series and could be biased at voltages up to 120 V.

Full integrated process to manufacture RF-MEMS and MMICs on GaN/Si substrate

Radio Frequency Micro-Electro-Mechanical System (RF-MEMS) represents a feasible solution to obtain very low power dissipation and insertion loss, very high isolation and linearity switch with respect to “solid state” technologies. In this paper, we demonstrate the full integration of RF-MEMS switches in the GaN-HEMT (Gallium Nitride/High Electron Mobility Transistor) fabrication line to develop RF-MEMS devices and LNA-MMIC (Low Noise Amplifier/Monolithic Microwave Integrated Circuit) prototype simultaneously in the same GaN wafer. In particular, two different coplanar wave (CPW) LNAs and a series of discrete RF-MEMS in ohmic-series and capacitive-shunt configuration have been fabricated. RF-MEMS performances reveal an insertion loss and isolation better than 1 and 15 dB, respectively, in the frequency range 20–50 GHz in the case of pure capacitive shunt switches and in the frequency range 5–35 GHz for the ohmic-series switches. Moreover, the GaN HEMT device shows an Fmax of about 38 GHz and a power density of 6.5 W/mm, while for the best LNA-MMIC we have obtained gain better than 12 dB at 6–10 GHz with a noise figure of circa 4 dB, demonstrating the integration achievability.

Methodology for Small-Signal Model Extraction of AlGaN HEMTs

Both large- and small-periphery AlGaN high- electron mobility transistors (HEMTs) will find applications in microwave systems from 2 to 40 GHz because of their superior power handling capability. A self-consistent approach is presented for the linear model's parameter extraction from measured S-parameters. The model for parasitics is selected to reflect loading from both the probe pads and the interconnect regions, including the air bridges. The objective is to accurately extract intrinsic model parameters as the device periphery is increased from 50 mum to 1 mm and to isolate the effects of device layouts, including air bridging the source regions. To accurately extract the shunt and series parasitics, the device must be represented in its ON- and OFF-states determined by the gate and drain bias. The intrinsic device capacitances are not negligible in the forward and beyond-pinchoff reverse bias states at zero drain bias and must be accounted for. With these corrections to the measured S-parameters, consistent results for the intrinsic device parameters are obtained with both small- and large-periphery AlGaN HEMTs.

Surface Morphology of Al0.3Ga0.7N/Al2O3-High Electron Mobility Transistor Structure

We present surface properties of buffer films (AIN and GaN) and Al0.3Gao.zN/Al2O3-High Electron Mobility Transistor (HEMT) structures with/without AIN interlayer grown on High Temperature (HT)-AIN buffer/Al2O3 substrate and Al2O3 substrate. We have found that the GaN surface morphology is step-flow in character and the density of dislocations was about 10(8)-10(9) cm(-2). The AFM measurements also exhibited that the presence of atomic steps with large lateral step dimension and the surface of samples was smooth. The lateral step sizes are in the range of 100-250 nm. The typical rms values of HEMT structures were found as 0.27, 0.30, and 0.70 nm. HT-AIN buffer layer can have a significant impact on the surface morphology of Al0.3Ga0.7N/Al2O3-HEMT structures.

High-speed MSM/HEMT and p-i-n/HEMT monolithic photoreceivers

The performance of monolithically integrated metal-semiconductor-metal/high electron-mobility transistor (MSM/HEMT) and p-i-n/HEMT photoreceivers is reported. p-i-n/HEMT photoreceivers have been designed and fabricated, resulting in measured transimpedances of 700 /spl Omega/, an 8.3-GHz bandwidth, and measured sensitivities of -17.7 dBm at 10 Gb/s and -15.8 dBm at 12 Gb/s for a 2/sup 31/ - 1 pattern length pseudorandom bit sequence at a bit error rate of 10/sup -9/. Low-noise MSM-based pbotoreceivers have also been designed and fabricated, and frequency response, noise, and sensitivity measurements have been performed. Sensitivities of -16.9, -13.1, and -10.7 dBm were obtained at 5, 8, and 10 Gb/s, respectively. A direct comparison of p-i-n- and MSM-based photoreceivers is undertaken on photoreceivers with matched responsivity and bandwidth. Measurement and theoretical analysis of circuit and device noise indicates an anomalous sensitivity penalty in MSM-based receivers that arises due to intersymbol interference.

35-GHz static and 48-GHz dynamic frequency divider ICs using 0.2-/spl mu/m AlGaAs/GaAs-HEMTs

Two static and two dynamic frequency dividers based on enhancement and depletion 0.2-/spl mu/m gate length AlGaAs/GaAs-high electron mobility transistor (HEMT) (f/sub T/=60 and 55 GHz) technology were designed and fabricated. High-speed operations up to 35 GHz for the static frequency dividers and 48 GHz for the dynamic dividers, respectively, have been achieved. The single-ended input and differential outputs to ground simplify many applications. The power consumption is 250 mW for the divide-by-two dividers and 350 mW for the divide-by-four dividers using two supply voltages of 4 and -2.5 V.

Modeling of InGaAs optical constants and its application to spectroscopic ellipsometry study of strained InGaAs/AlGaAs based structures

There is a broad spectrum of electronic devices, e.g., high electron mobility, heterojunction bipolar (HBTs) and modulation doped field effect (MODFETs) transistors, and optoelectronic devices, e.g., low-threshold quantum-well (QW) lasers, which employ strained InyGa1-yAs layers to improve device performance due to the enhanced flexibility in the electronic structure. These devices have very promising applications. For example, the ultra-low threshold lasers are going to play a major role in computer interconnect circuits due to their low-power consumption. Strainlayer InGaAs/GaAs QW lasers are of considerable interest as a possible candidate for pumping the upper states of Er-doped silica fiber amplifiers of optical networks.

Gallium aluminium arsenide heterostructure lasers: factors affecting catastrophic degradation : G. D. Henshall. Solid-St. Electron.20, p. 595 (1977)

Identification and characterization of a single, deep trap causing large increases in the on-resistance of GaN-on-Si power metal-insulator-semiconductor-high electron mobility transistors (MISHEMTs) is reported. This is achieved by using HEMT-based deep level optical spectroscopy (DLOS) and related methods in conjunction with high voltage off-state VDS switching up to 400 V. A trap with an activation energy of ~ EC − 2 eV that is physically located in the drain-access region of the MISHEMT is shown to be the primary source of an increase of the dynamic on-resistance increase by as much as ~ 9 times at 400 V operation. Comparisons of trap signatures extracted from the MISHEMT with capacitance-based DLOS measurements of simple Schottky-diode test-structures showing the same, dominant trap signature suggests that the physical defect is located within the GaN buffer and is not a surface or insulator-related defect. A buffer trap based model is presented to explain the observed on-resistance degradation effects in the MISHEMTs during high voltage switching.