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Maintaining high average fields between the gate and drain is imperative in achieving near theoretical performance in ultra-wide band gap semiconductors like $\beta $ -Ga2O3. In this letter we report on a field management strategy to reduce the peak electric field at the drain side corner of the gate by using a composite dielectric layer consisting of an extreme permittivity dielectric like BaTiO3 and a low- $\kappa $ dielectric like SiO2 overlapped over the gate electrode. Using this strategy in $\beta $ -(Al0.18Ga0.82)2O3/ Ga2O3 double heterojunction field effect transistor, we achieved a record average breakdown field of 5.5 MV/cm at a gate-drain spacing of $1.15~\mu \text{m}$ along with an improved power figure of merit of 408 MW/cm2. The reported works shows the effectiveness of integrating extreme dielectric materials with ultra-wide band gap semiconductors in significantly improving breakdown performance.

The performance of ultra-wide bandgap semiconductors like ${\beta }$ -Ga2O3 is critically dependent on achieving high average electric fields within the active region of the device. In this article, we show that dielectrics like BaTiO3 with extremely high dielectric constant can provide an efficient field management strategy by improving the uniformity of electric field profile within the gate–drain region of lateral field-effect transistors. Using this strategy, we achieved high average breakdown field of 1.5 and 4 MV/cm at gate–drain spacing ( ${L}_{\text {gd}}$ ) of 6 and $0.5~{\mu }\text{m}$ , respectively in ${\beta }$ -Ga2O3, at a high channel sheet charge density of $1.6\,\,{\times }\,\,10^{{13}}$ cm−2. The high channel charge density along with the high breakdown field enabled a record power figure of merit ( ${V}_{\text {br}}^{{2}}/{R}_{\text {ON}}$ ) of 376 MW/cm2 at a gate–drain spacing of ${3}~{\mu }\text{m}$ .

We introduce a deep-recessed gate architecture in $\beta $ -Ga2O3 delta-doped field-effect transistors (FETs) for improvement in dispersion and breakdown properties. The device design incorporates an unintentionally doped (UID) $\beta $ -Ga2O3 layer as the passivation dielectric. To fabricate the device, the deep-recess geometry was developed using BCl3 plasma-based etching at ~5 W reactive ion etching (RIE) power to ensure minimal plasma damage. Etch damage incurred with plasma etching was mitigated by annealing in vacuum at temperatures above 600 °C. A gate-connected field-plate edge termination was implemented for efficient field management. Negligible surface dispersion with lower knee walkout at high ${V}_{{\text {DS}}}$ , and better breakdown characteristics compared to their unpassivated counterparts were achieved. A three-terminal OFF-state breakdown voltage of 315 V, corresponding to an average breakdown field of 2.3 MV/cm was measured. The device breakdown was limited by the field-plate/passivation edge and presents scope for further improvement. This demonstration of epitaxially passivated FET is a significant step for $\beta $ -Ga2O3 technology since the structure simultaneously provides control of surface-related dispersion and excellent field management.

We highlight the flexibility of two-dimensional (2D) materials for advancing current technologies through the introduction of 2D Raman thermography (2DRT). 2DRT combines monolayer materials and Ram...

A novel edge-termination concept using extreme permittivity dielectrics is proposed to effectively manage electric fields in vertical power-devices. This method is expected to be particularly significant for wide band-gap semiconductors, where field termination is a significant challenge due to material and process limitations. Detailed two-dimensional device simulation is used to prove the efficacy of this idea, and to demonstrate that peak electric fields are significantly reduced by this method. We also show an analytical model that gives an intuitive picture into the mechanism of high-permittivity dielectric field plate. Low process complexity and flexibility in the design of power devices can be achieved. We show that junction termination efficiency can be increased from 22.7% (no junction termination) and 50% (conventional field plate) to 73% (high-permittivity-terminated device).

High-current molecular beam epitaxial perovskite oxide semiconductor BaTiO3/BaSnO3 heterostructure field effect transistors on SrTiO3 substrates were developed. Record high current density of $\text{I}_{{\mathrm{max}}} =406.7$ mA/mm, maximum transconductance $\text{g}_{{{\text {m}}}} =72.3$ mS/mm were achieved in a field effect transistor with gate length $\text{L}_{{{\text {g}}}} = 0.64\,\,\mu \text{m}$ , and source-drain spacing $\text{L}_{{{\text {sd}}}} = 3.5\,\,\mu \text{m}$ . The device has a low threshold voltage of $\text{V}_{{{\text {th}}}}= - 4.5$ V and the capability to modulate $5.7\times 10^{{{{13}}}}$ cm $^{{-{2}}}$ electron density in the BaSnO3 channel. The high channel current and gate modulation efficiency are attributed to the high mobility and charge density in the BaSnO3 channel and the utilization of high-k BaTiO3 ( $\varepsilon $ is in the range of 425 and 387 as the electric field increases from 46 to 85 kV/cm) layer as the gate dielectric for charge modulation. Though the device suffers from low current ON/OFF ratio and a large subthreshold swing due to the gate leakage resulted from threading dislocations, this work demonstrates the great potential of perovskite semiconductors for electronic device applications.

We investigated the thermal characteristics of a recently developed delta-doped $\beta $ -Ga2O3 MESFET using thermoreflectance imaging technique, which enabled temperature measurement with ~250 nm spatial and ~400 ns temporal resolution. We measured the temperature contours on source, drain and gate pads, and estimated peak temperature at different bias conditions, and calculated the thermal time constants of these devices, which can be used to predict their transient thermal behavior. The steady-state temperature is measured to be ~199° C at the gate-center at power =2.56W/mm. A 3-D thermal model combined with a device thermodynamic carrier transport model, which is in good agreement with measurements, was used to predict the temperature profile inside the device. Our analysis establishes that the temperature measured at the gate-center is lower than the overall peak temperature in the device, and the difference between peak and gate-center temperature is higher for the lower gate-voltages at similar power.

III-Nitride light emitting diodes (LEDs) are widely used in a range of high efficiency lighting and display applications, which has enabled significant energy savings in the last decade. Despite the wide application of GaN LEDs, transport mechanisms across InGaN/GaN heterostructures in these devices are not well explained. Fixed polarization sheet charges at InGaN/GaN interfaces lead to large interface dipole charges, which create large potential barriers to overcome. One-dimensional models for transport across such heterostructures predict turn-on voltages that are significantly higher than that found in real devices. As a result, conventional models for transport cannot predict the performance of new designs such as for longer wavelength LEDs or for multi-quantum well LEDs. In this work, we show that incorporating low and high indium compositions within quantum wells at the submicrometer scale can provide an accurate prediction of the characteristics of GaN/InGaN light emitting diodes.

A 2-D electrothermal model of delta-doped b eta-gallium oxide ( $\beta $ -Ga2O3) metal–semiconductor field-effect transistor (MESFET) is developed by using TCAD Sentaurus to investigate its electrical and thermal characteristics. The temperature and electric field-dependent electron mobility model is incorporated to predict I – V characteristics of the FET, which are in good agreement with the measured I – V characteristics. We investigated the effect of bias voltages on an electric field, a current path, a volumetric heat generation profile, and a peak temperature at a given total heat dissipation. The peak temperature is observed to be significantly different at the same power dissipation but different bias conditions, e.g., the peak temperature is ~9 K higher when the drain-to-source voltage ( V ds) = 25 V and the gate-to-source voltage ( V gs) = −6 V compared with V ds = 8.3 V and V gs = 2 V at the total power dissipation of 1.16 W/mm. This difference is attributed to the change in the electron Joule heating profile with the applied bias voltage. The effects of the location of the delta-doping layer, the gate–drain spacing, and the source–drain spacing are investigated to guide a future device fabrication. The variation in these parameters mainly affects electrical characteristics such as ON-resistance, saturation current, threshold voltage, and so on. The thermal characteristics, such as peak temperature, temperature profile, and so on, are not significantly affected at a low-power dissipation.

Owing to its strong ionic character coupled with a light electron effective mass, $\ensuremath{\beta}\text{\ensuremath{-}}{\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ is an unusual semiconductor where large electric fields (approximately 1--6 MV/cm) can be applied while still maintaining a dominant excitonic absorption peak below its ultrawide band gap (${E}_{g}$ \ensuremath{\sim} 4.6--4.99 eV). This provides a rare opportunity in the solid state to examine exciton and carrier self-trapping dynamics in the strong-field limit at steady state. Under sub-band-gap photon excitation, we observe a field-induced redshift of the spectral photocurrent peak associated with exciton absorption and a thresholdlike increase in peak amplitude at high field associated with self-trapped hole ionization. The field-dependent spectral response is quantitatively fitted with an exciton-modified Franz-Keldysh effect model, which includes the electric-field-dependent exciton-binding energy due to the quadratic Stark effect. Saturation of the spectral redshift with reverse bias is observed exactly at the onset of dielectric breakdown, providing a spectral means to detect and quantify the local electric field and dielectric breakdown behavior in $\ensuremath{\beta}\text{\ensuremath{-}}{\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$. Additionally, the field-dependent responsivity provides an insight into the photocurrent-production pathway, revealing the photocurrent contributions of self-trapped excitons (STXs) and self-trapped holes (STHs) in $\ensuremath{\beta}\text{\ensuremath{-}}{\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$. Photocurrent and p-type transport in $\ensuremath{\beta}\text{\ensuremath{-}}{\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ are quantitatively explained by field-dependent tunnel ionization of excitons and self-trapped holes. We employ a quantum-mechanical model of the field-dependent tunnel ionization of STXs and STHs in $\ensuremath{\beta}\text{\ensuremath{-}}{\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ to model the nonlinear field dependence of the photocurrent amplitude. Fitting to the data, we estimate an effective mass of valence-band holes (18.8${m}_{0}$) and an ultrafast self-trapping time of holes (0.045 fs). This indicates that minority-hole transport in $\ensuremath{\beta}\text{\ensuremath{-}}{\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ can only arise through tunnel ionization of STHs under strong fields.

We investigate voltage breakdown of a $\beta $ -(Al0.22Ga0.78)2O3/Ga2O3 modulation-doped field-effect transistor with a gate-connected field-plate and silicon nitride (SiNx) as the passivation layer. Breakdown characteristics were found to be limited by the Schottky gate. We demonstrate a high breakdown voltage of 1.37 kV for a gate-to-drain separation ( ${L} _{\text {GD}}$ ) of $16~\mu \text{m}$ with a specific ON-resistance $\vphantom {\int ^{AAAAA^{AAA}}}$ of 120.1 $\text{m}\Omega \cdot \text {cm}^{{2}}$ . A high average electric field of 3.9 MV/cm is extracted for ${L} _{\text {GD}}={320}$ nm. The reported results suggest SiNx as a potential passivation dielectric for Ga2O3.

As an ultra-wide bandgap semiconductor, $\beta $ -Ga2O3 has attracted great attention for high-power, high-voltage, and optoelectronic applications. However, until now, high-frequency performance of gallium oxide devices has been limited to relatively low current gain cutoff frequencies below 5 GHz. Here, we show that highly localized delta-doping designs can enable high-sheet-charge density to enable devices with short gate lengths that allow high-frequency operation. Field-effect transistors with a gate length of 120 nm on such delta-doped $\beta $ -Ga2O3 are reported here with extrinsic unity current gain frequency of 27 GHz. The device has a peak drain current of 260 mA/mm, transconductance (gm) of 44 mS/mm, and three-terminal off-state breakdown voltage of 150 V. These results demonstrate that the potential of $\beta $ -Ga2O3 for future RF and millimeter-wave device applications.

We report on the high-field transport characteristics and saturation velocity in a modulation-doped $\beta $ -(AlxGa1–x)2O3/Ga2O3 heterostructure. The formation of a 2-D electron gas (2DEG) in the modulation-doped structure was confirmed from the Hall measurements, and the 2DEG channel mobility increased from 143 cm $^{2}/\text{V}\cdot \text{s}$ at room temperature to 1520 cm $^{2}/\text{V}\cdot \text{s}$ at 50 K. The high electron mobility at 50 K made it feasible to achieve velocity saturation inside the channel. The saturation velocity was estimated based on both pulsed current–voltage measurements and small-signal radio frequency (RF) measurements. The measured velocity–field profile suggested a saturation velocity above $1.1\times 10^{7}$ cm/s at 50 K. The small-signal RF characteristics were measured for the fabricated modulation-doped field-effect transistors with a Pt-based Schottky contact. The current gain cutoff frequency ( $\text{f}_{\text {t}}$ ) and maximum oscillation frequency ( $\text{f}_{\text {max}}$ ) showed significant increases from 4.0/11.8 GHz at room temperature to 17.4/40.8 GHz at 50 K for the device with gate length of $\text{L}_{{\textsf {G}}} = 0.61\,\,\mu \text{m}$ . The analysis of the low temperature $\text{f}_{\text {t}}$ based on device simulations indicated a peak velocity of $1.2\times 10^{7}$ cm/s. The three-terminal off-state breakdown measurement further suggested an average breakdown field of 3.22 MV/cm. The high saturation velocity and high breakdown field in $\beta $ -Ga2O3 make it a promising candidate for high-power and high-frequency device applications.

The design and modeling of dielectric superjunction transistors using combinations of ultrahigh permittivity materials and high-mobility materials are described. We show that placing high dielectric permittivity materials in the gate–drain depletion region can reduce electric field variations by screening the field due to depleted charges. This enables simultaneously high sheet charge density and breakdown voltage for scaled field-effect transistors. Using detailed 2-D device simulation of dc and high frequency characteristics, we show that extreme dielectric constant engineering provides unique opportunities for transistor design and has the potential to perform better than state-of-the-art millimeter-wave and terahertz frequency transistors.

In this letter, we demonstrate high-performance vertical solar-blind Schottky photodetectors on MBE-grown homoepitaxial (010)-oriented $\beta $ -Ga2O3 films. The structure, consisting of (100 nm) $\beta $ -Ga2O3/(60 nm) $\text{n}^{++} \beta $ -Ga2O3, was grown on a Fe-doped insulating (010) $\beta $ -Ga2O3 substrate. Ni/Au and indium were used as the Schottky and Ohmic contacts, respectively. The devices exhibited a rectification ratio of ~107 with turn-on voltage ~1 V and an ideality factor of 1.31. The extracted Schottky barrier height was 1.4 eV. The photodetectors showed low dark current of 0.3 nA at 5 V with a photo-to-dark current ratio of ~102 at 0 V. The devices exhibited a zero-bias responsivity of 4 mA/W at 254 nm corresponding to an external quantum efficiency ~3 %, with a UV-to-visible rejection ratio >103, showing true solar-blind operation. The transient response of the devices indicated rise/fall times of ~100 ms. Temperature-dependent current–voltage characteristics agree with the thermionic emission model.

This presentation will give an overview of our recent work on materials growth and device engineering of 𝛽-Ga2O3 electronic devices. We will discuss the design and properties of advanced modulation-doped (Al,Ga)2O3/Ga2O3 structures with high sheet charge density and excellent transport properties. We will then outline novel strategies for realizing high breakdown fields and low resistance within devices, and outline design, growth, and characteristics of state-of-art Gallium Oxide devices, including scaled transistors with cutoff frequency of 27 GHz, and transistors with a power switching figure of merit of 586 MW/cm2 and breakdown voltage of 660V.

Threshold voltage instability was observed on $\beta $ -Ga2O3 transistors using double-pulsed current–voltage and constant drain current deep level transient spectroscopy (DLTS) measurements. A total instability of 0.78 V was attributed to two distinct trap levels, at ${E}_{C}$ -0.70 and ${E}_{C}$ -0.77 eV, which need to be mitigated for future applications. The traps are likely located near the gate–drain edge and below the delta-doped layer, which is determined through the DLTS technique and an understanding of the fill and empty biasing conditions. The trap modulation was consistent with a gate leakage-based trap filling mechanism, which was demonstrated. It is likely that Fe is playing a role in the observed dispersion due to the close proximity of the Fe substrate.

We report silicon delta-doped $\beta $ -Ga2O3 metal semiconductor field effect transistors (MESFETs) with source–drain ohmic contacts formed by patterned regrowth of n-type Ga2O3. We show that regrown n-type contacts can enable a lateral low-resistance contact to the two-dimensional electron gas channel, with contact resistance lower than $1.5~\Omega $ -mm. The fabricated MESFET has a peak drain current ( ${I} _{D,\text{MAX}}$ ) of 140 mA/mm, transconductance ( ${g} _{m}$ ) of 34 mS/mm, and 3-terminal off-state breakdown voltage of 170 V. The proposed device structure could provide a promising path towards vertically scaled $\beta $ -Ga2O3 field effect transistors.

In situ etching using Ga flux in an ultra-high vacuum environment like molecular beam epitaxy is introduced as a method to make high aspect ratio three-dimensional (3D) structures in β-Ga2O3. Etching of β-Ga2O3 due to excess Ga adatoms on the epilayer surface had been viewed as non-ideal for epitaxial growth especially since it results in plateauing and lowering of the growth rate. In this study, we use this well-known reaction from epitaxial growth to intentionally etch β-Ga2O3. We demonstrate etch rate ranging from 2.9 to 30 nm/min with the highest reported etch rate being only limited by the highest Ga flux used. Patterned in situ etching is also demonstrated and used to study the effect of fin orientation on the sidewall profiles and dopant (Si) segregation on the etched surface. Using in situ Ga etching, we also demonstrate 150 nm wide fins and 200 nm wide nanopillars with high aspect ratio. This etching method could enable future development of highly scaled vertical and lateral 3D devices in β-Ga2O3.

AlGaN channel transistors are promising candidates for high power RF transistors due to their superior material properties. The larger breakdown field and similar saturation velocity compared to GaN make AlGaN channel transistors potentially capable of delivering higher power density at high frequencies. So far the highest reported $\mathrm{f}_{\mathrm{T}}$ is 28 GHz on Al 0.85 Ga 0.15 N/Al 0.70 Ga 0.30 N transistors with RF power density of 0.3 W/mm at 3 GHz [1]. The major obstacle to achieve high RF performance is the challenge to form good ohmic contacts to Al-rich AlGaN. Here, we show significantly better small and large signal RF performance than what have been reported on high Al-composition AlGaN transistors with regrown side contacts.

$\beta$ -Ga203 is an emerging ultra-wide bandgap (~4.7 eV) semiconductor with great potential for power electronics. The large breakdown electric field (6–8 MV/cm predicted) due to wide band gap combining with electron mobility of 250 −300 cm2/Vs offers a higher figure of merit for power electronic than SiC and GaN. In the absence of a p-type dopant, the low Schottky barrier height is a fundamental challenge for achieving the theoretically predicted limit for $\beta$ -Ga 2 O 3 power electronic devices. $\beta$ -Ga 2 O 3 Schottky barrier diodes with more than 1 kV breakdown voltage have been demonstrated but the maximum breakdown field in these devices was limited below 3.5 MV/cm due to metal to Ga203 Schottky barrier height (1.5-1.7 eV). In this work, we design and demonstrate the use of high dielectric heterojunctions to engineer electrostatics and transport within the diode and achieve high breakdown electric field (5.6 MV/cm) in a metal/BaTiO 3 $\beta$ -Ga 2 O 3 heterojunction diode. This is the highest reported breakdown field for any $\beta$ -Ga 2 O 3 vertical diode, and it provides a general framework for future design of unipolar high voltage diodes based on wide and ultra-wide bandgap semiconductors.

We report on the first demonstration of epitaxial passivation for $\beta$ -Ga 2 O 3 field effect transistors (FETs) with a gate connected field-plate. $\beta$ -Ga 2 O 3 is a promising material for next generation high power and RF electronics, enabled by its large band gap $(\mathrm{E}_{\mathrm{g}}=4.5-4.9\ \mathrm{eV})$ , high breakdown field (8 MV/cm) and high electron velocity [1] [2]. In this work, we have used a delta-doped channel design since it allows scaled device topology while preserving relatively high mobility.

Gallium oxide has potential to emerge as a better alternative to wide bandgap materials such as GaN, SiC etc. for radio frequency and power electronics applications. It can achieve higher breakdown voltage and efficiency than GaN and SiC due to its significantly higher bandgap and Baliga's figure of merit. In this work, we have studied electrical and thermal characteristics of a delta-doped $\beta$ -Ga 2 O 3 Field Effect Transistor (FET). In this FET, a thin layer of Ga 2 O 3 is grown epitaxially on Fe doped semi-insulating Ga 2 O 3 substrate; all grown in (010) direction. First, a 2-D electro-thermal model is developed and numerically computed electrical characteristics are matched with the measurements. The Thermodynamic model in Sentaurus TCAD is used for these numerical simulations. Temperature profile and location of hot-spot in the device were determined. The maximum drain current of 154.4 mA/mm of channel width was predicted at drain-source voltage of 10 V and gate-source voltage of 2 V. The peak temperature of device computed using 2-D model is 475 K at this biased voltage just below the gate edge that is near the drain side. Second, a 3-D model was used to predict peak temperature more accurately. 3-D model predicts peak temperature at the specified bias condition to be 416 K. Thus, we highlighted that 2-D model over-predicts peak temperature. Finally, we explored two different passive cooling mechanisms– (1) replacement of substrate with a higher thermal conductivity substrate and (2) addition of a passivation layer on top of the semiconducting Ga 2 O 3 layer. First method is observed to be more effective in reducing the peak and overall temperature in the device.

Ultra-wide bandgap β-gallium oxide (Ga2O3) devices are of considerable interest with potential applications in both power electronics and radio frequency devices. However, current Ga2O3 device technologies are limited by the material's low intrinsic electron mobility and thermal conductivity. The former problem can be addressed by employing modulation-doped β-(AlxGa1−x)2O3/Ga2O3 heterostructures in the device architecture. In this work, (AlxGa1−x)2O3/Ga2O3 modulation-doped field effect transistors (MODFETs) have been investigated from a thermal perspective. Thermoreflectance thermal imaging was used to characterize the self-heating of the MODFETs. The (Al0.18Ga0.82)2O3 thermal conductivity (3.1–3.6 W/mK) was determined using a frequency domain thermoreflectance technique. Electro-thermal modeling was used to discern the effect of design parameters such as substrate orientation and channel length on the device self-heating behavior. Various thermal management schemes were evaluated using the electro-thermal device model. From an electro-thermal co-design perspective, the improvement in electrical performance followed by the mitigation of self-heating was also studied. For example, by employing a Ga2O3-on-SiC composite wafer, which was fabricated in this work, a 50% increase in power handling capability can be achieved as compared to a homoepitaxial device. Furthermore, flip-chip heterointegration and double-sided cooling approaches can lead to more than 2× improvement in the power handling capability. Using an augmented double-sided cooling design that includes nanocrystalline diamond passivation, a 5× improvement in the power handling capability can be accomplished, indicating the potential of the technology upon implementation of a suitable thermal management scheme.

This report discusses the design and demonstration of β-(Al0.17Ga0.83)2O3/Ga2O3 modulation doped heterostructures to achieve high sheet charge density. The use of a thin spacer layer between the Si delta-doping and the heterojunction interface was investigated in a β-(AlGa)2O3/Ga2O3 modulation doped structure. It is shown that this strategy enables a higher two-dimensional electron gas (2DEG) sheet charge density up to 4.7 × 1012 cm−2 with an effective mobility of 150 cm2/V s. The presence of a degenerate 2DEG channel was confirmed by the measurement of a low temperature effective mobility of 375 cm2/V s and the lack of carrier freeze out from low temperature capacitance voltage measurements. The electron density of 4.7 × 1012 cm−2 is the highest reported 2DEG density obtained without parallel conducting channels in a β-(AlxGa(1−x))2O3/Ga2O3 heterostructure system.

We report a gate recessed Al0.7Ga0.3N/Al0.5Ga0.5N heterostructure field effect transistor (HFET) with a graded contact cap layer grown by metal organic chemical vapor deposition (MOCVD) on AlN/Sapphire substrate. A low specific contact resistivity ρc of 2.1 × 10−5 Ω·cm2 is demonstrated with current injection from the top of the Al0.7Ga0.3N barrier to the Al0.5Ga0.5N channel. The device with a gate length of 160 nm exhibits a drain current density at gate shorted to source (ID,SS) of 420 mA/mm, a cutoff frequency fT of 20 GHz, and a maximum oscillation frequency (fmax) of 40 GHz. The same device has a three terminal off-state gate-to-drain breakdown voltage of 170 V, corresponding to an average breakdown field (FBR) of 2.8 MV/cm between the gate and drain, due to drain induced barrier lowering effect. Devices with a gate length of 1 µm demonstrate a gate to drain breakdown voltage of 195 V or an average breakdown field of 3.9 MV/cm. This work provides a way to make ohmic contacts to Al-rich AlGaN channel heterojunction transistors for high power and high frequency applications.

In this Letter, we demonstrate a Pt/BaTiO3/Al0.58Ga0.42N lateral heterojunction diode with enhanced breakdown characteristics. By using BaTiO3, a high-k material, as a dielectric material between the anode and semiconductor, the peak electric field at the anode edge near the cathode was significantly reduced and an average breakdown field exceeding 8 MV/cm was achieved for devices with an anode to cathode spacing of

Gallium Nitride electronics based on the AlGaN/GaN high electron mobility transistor structure is approaching intrinsic limits. Future mm-wave and THz technology requires highly efficient and linear amplifiers that can deliver high power density. This presentation will outline the potential and recent work of next-generation wide band gap transistors based on ultra-wide band gap semiconductors for high frequency applications. Detailed DC and high frequency 2-dimensional modeling of ultra-wide band gap semiconductor devices show that the predicted power density, gain, and efficiency of these devices have the potential to be better than cutting-edge GaN-based devices at mm-wave and THz frequencies. We will discuss the principal challenges for realization of these devices and outline the design and demonstration of advanced high Al-composition AlGaN based transistors, where researchers have used novel epitaxial designs to enable efficient injection and extraction of carriers. This has enabled the state-of-the-art current density and breakdown characteristics of AlGaN-channel devices to increase significantly in recent years.

Gallium oxide (Ga 2 O 3 ) field-effect transistors (FETs) have high potential for future RF and power devices due to their superior power switching capabilities, high breakdown field, and opportunities for single crystal substrate fabrication. However, the high heat dissipation and inefficient heat removal from the channel area of these FETs can limit the device performance and cause reliability issues. In this work, we investigate the thermal characteristics of Ga 2 O 3 based FETs by performing transient temperature measurements using a thermo-reflectance imaging system. The transient temperature distribution in the channel and metallic contacts is obtained at different voltages. We analyze the temperature distribution and the location of hot spots inside the channel, and establish hot spot temperature dependence with the gate voltage. High temperature rise at hot spots is observed in the channel area even at low power levels, which is a consequence of the low thermal conductivity of Ga 2 O 3 . Investigation of thermal characteristics of these FETs is crucial to develop efficient thermal management solution and improving the reliability of Ga 2 O 3 devices. It will also help in better device and package design considering thermal aspects.

In this report, we demonstrate high spectral responsivity (SR) in MBE grown epitaxial \b{eta}-Ga2O3-based solar blind MSM photodetectors (PD). (-2 0 1)-oriented \b{eta}-Ga2O3 thin film was grown by plasma-assisted MBE on c-plane sapphire substrates. MSM devices fabricated with Ni/Au contacts in an interdigitated geometry were found to exhibit peak SR > 1.5 A/W at 236-240 nm at a bias of 4 V with a UV to visible rejection ratio > 105. The devices exhibited very low dark current < 10 nA at 20 V and showed no persistent photoconductivity (PPC) as evident from the sharp transients with a photo-to-dark current ratio > 103. These results represent the state-of-art performance for MBE-grown \b{eta}-Ga2O3 MSM solar blind detector.

Modulation-doped heterostructures are a key enabler for realizing high mobility and better scaling properties for high performance transistors. We report the realization of a modulation-doped two-dimensional electron gas (2DEG) at the beta-(Al0.2Ga0.8)(2)O-3/Ga2O3 heterojunction by silicon delta doping. The formation of a 2DEG was confirmed using capacitance voltage measurements. A modulation-doped 2DEG channel was used to realize a modulation-doped field-effect transistor. The demonstration of modulation doping in the beta-(Al0.2Ga0.8)(2)O-3/Ga2O3 material system could enable heterojunction devices for high performance electronics. Published by AIP Publishing.

We report on the origin of high Si flux observed during the use of Si as a doping source in plasma assisted MBE growth of β-Ga2O3. We show on the basis of secondary ion mass spectroscopy analysis that Si flux is not limited by the vapor pressure of Si but by the formation of volatile SiO. The low sublimation energy of SiO leads to a weak dependence of the SiO flux of Si cell temperature and a strong dependence on the background oxygen pressure. Extended exposure to activated oxygen results in reduction of SiO flux due to the formation of SiO2 on the Si surface. The work reported provides key understanding for incorporating Si into future oxide-based semiconductor heterostructure and device MBE growth.

Two buffer traps at EC-0.7 eV and EC-0.8 eV have been individually identified as causing threshold voltage and on-resistance instabilities in β-Ga2O3 Si ∂-doped transistors grown by plasma-assisted molecular beam epitaxy (PAMBE) on semi-insulating Fe doped β-Ga2O3 substrates. The instabilities are characterized using double-pulsed current-voltage and isothermal constant drain current deep level transient spectroscopy. The defect spectra are compared between transistors grown using two different unintentionally doped buffer layer thicknesses of 100 nm and 600 nm. The EC-0.8 eV trap was not seen using the thicker buffer and is shown to correlate with the presence of residual Fe in thePAMBE buffer layer. The EC-0.7 eV trap was unchanged in concentration and is revealed as the dominating source of the threshold voltage instability. This trap is consistent with the characteristics of a previously reported intrinsic point defect [Ingebrigtsen et al., APL Mater. 7, 022510 (2019)]. The EC-0.7 eV trap is responsible for ∼70% of the total threshold voltage shift in the 100 nm thick buffer transistor and 100% in the 600 nm thick buffer transistor, which indicates growth optimization is needed to improve β-Ga2O3 transistor stability.Two buffer traps at EC-0.7 eV and EC-0.8 eV have been individually identified as causing threshold voltage and on-resistance instabilities in β-Ga2O3 Si ∂-doped transistors grown by plasma-assisted molecular beam epitaxy (PAMBE) on semi-insulating Fe doped β-Ga2O3 substrates. The instabilities are characterized using double-pulsed current-voltage and isothermal constant drain current deep level transient spectroscopy. The defect spectra are compared between transistors grown using two different unintentionally doped buffer layer thicknesses of 100 nm and 600 nm. The EC-0.8 eV trap was not seen using the thicker buffer and is shown to correlate with the presence of residual Fe in thePAMBE buffer layer. The EC-0.7 eV trap was unchanged in concentration and is revealed as the dominating source of the threshold voltage instability. This trap is consistent with the characteristics of a previously reported intrinsic point defect [Ingebrigtsen et al., APL Mater. 7, 022510 (2019)]. The EC-0.7 eV trap is respons...

BaSnO_{3}, a high mobility perovskite oxide, is an attractive material for oxide-based electronic devices. However, in addition to low-field mobility, high-field transport properties such as the saturation velocity of carriers play a major role in determining device performance. We report on the experimental measurement of electron saturation velocity in La-doped BaSnO_{3} thin films for a range of doping densities. Predicted saturation velocities based on a simple LO-phonon emission model using an effective LO phonon energy of 120 meV show good agreement with measurements of velocity saturation in La-doped BaSnO_{3} films.. Density-dependent saturation velocity in the range of 1.6x10^{7} cm/s reducing to 2x10^{6} cm/s is predicted for {\delta}-doped BaSnO3 channels with carrier densities ranging from 10^{13} cm^{-2} to 2x10^{14} cm^{-2} respectively. These results are expected to aid the informed design of BaSnO3 as the active material for high-charge density electronic transistors., Comment: 23 pages, 10 figures, 2 tables

An Al0.75Ga0.25N/Al0.6Ga0.4N heterostructure field effect transistor with graded MBE-regrown contacts is designed, grown, and fabricated on AlN/sapphire substrate. Maximum drain current density (ID,max) of 460 mA mm−1 was obtained on transistors with gate length of 130 nm. The small signal measurement shows current/power gain cutoff frequency (fT/fmax) of 40 GHz/58 GHz, respectively. Parasitic resistance is found to be a significant factor limiting the frequency performance of the devices. The high frequency performance of devices with high Al concentration AlGaN channel demonstrate potential for high power and high frequency applications.

We report on the effect of iron (Fe)-doped semi-insulating buffers on the electron transport and DC-RF dispersion in Si delta (δ)-doped β-Ga2O3 metal-semiconductor field effect transistors. The effect of the distance between the 2-dimensional electron gas and the Fe-doped region was investigated, and Fe doping in the buffer was found to have a significant effect on the transport properties. It was found that buffers thicker than 600 nm can enable better transport and dispersion properties for field effect transistors, while maintaining relatively low parasitic buffer leakage. This work can provide guidance for the use of Fe-doped insulating buffers for future Ga2O3 based electronics.

In this work, we demonstrate modulation-doped β-(AlxGa1-x)2O3/Ga2O3 double heterostructure field effect transistors. The maximum sheet carrier density for a two-dimensional electron gas (2DEG) in a β-(AlxGa1-x)2O3/Ga2O3 heterostructure is limited by the conduction band offset and parasitic channel formation in the barrier layer. We demonstrate a double heterostructure to realize a β-(AlxGa1-x)2O3/Ga2O3/(AlxGa1-x)2O3 quantum well, where electrons can be transferred from below and above the β-Ga2O3 quantum well. The confined 2DEG charge density of 3.85 × 1012 cm−2 was estimated from the low-temperature Hall measurement, which is higher than that achievable in a single heterostructure. Hall mobilities of 1775 cm2/V·s at 40 K and 123 cm2/V·s at room temperature were measured. Modulation-doped double heterostructure field effect transistors showed a maximum drain current of IDS = 257 mA/mm, a peak transconductance (gm) of 39 mS/mm, and a pinch-off voltage of −7.0 V at room temperature. The three-terminal off-state breakdown measurement on the device with a gate-drain spacing (LGD) of 1.55 μm showed a breakdown voltage of 428 V, corresponding to an average breakdown field of 2.8 MV/cm. The breakdown measurement on the device with a scaled gate-drain spacing of 196 nm indicated an average breakdown field of 3.2 MV/cm. The demonstrated modulation-doped β-(AlxGa1-x)2O3/Ga2O3 double heterostructure field effect transistor could act as a promising candidate for high power and high frequency device applications.

We demonstrate zero-bias spectral responsivity in MBE-grown β-Ga2O3 planar UV-C detector with good linearity up to optical power density of 4.6 mW cm−2. Devices with asymmetrical metal contacts were realized on 150 nm thick β-Ga2O3 films on sapphire. The device exhibited a spectral responsivity of 1.4 mA W−1 at 255 nm under zero-bias condition, dark current

In this work, we demonstrate a high mobility two-dimensional electron gas (2DEG) formed at the β-(AlxGa1-x)2O3/Ga2O3 interface through modulation doping. Shubnikov-de Haas (SdH) oscillations were observed in the modulation-doped β-(AlxGa1-x)2O3/Ga2O3 structure, indicating a high-quality electron channel formed at the heterojunction interface. The formation of the 2DEG channel was further confirmed by the weak temperature dependence of the carrier density, and the peak low temperature mobility was found to be 2790 cm2/Vs, which is significantly higher than that achieved in bulk-doped Beta-phase Gallium Oxide (β-Ga2O3). The observed SdH oscillations allowed for the extraction of the electron effective mass in the (010) plane to be 0.313 ± 0.015 m0 and the quantum scattering time to be 0.33 ps at 3.5 K. The demonstrated modulation-doped β-(AlxGa1-x)2O3/Ga2O3 structure lays the foundation for future exploration of quantum physical phenomena and semiconductor device technologies based on the β-Ga2O3 material system.

We report (010)-oriented β-Ga2O3 bevel-field-plated mesa Schottky barrier diodes grown by low-pressure chemical vapor deposition (LPCVD) using a solid Ga precursor and O2 and SiCl4 sources. Schottky diodes with good ideality and low reverse leakage were realized on the epitaxial material. Edge termination using beveled field plates yielded a breakdown voltage of −190 V, and maximum vertical electric fields of 4.2 MV/cm in the center and 5.9 MV/cm at the edge were estimated, with extrinsic R ON of 3.9 mΩcm2 and extracted intrinsic R ON of 0.023 mΩcm2. The reported results demonstrate the high quality of homoepitaxial LPCVD-grown β-Ga2O3 thin films for vertical power electronics applications, and show that this growth method is promising for future β-Ga2O3 technology.

We report silicon delta doping in Gallium Oxide (\b{eta}-Ga2O3) grown by plasma assisted molecular beam epitaxy using a shutter pulsing technique. We describe growth procedures that can be used to realize high Si incorporation in an oxidizing oxygen plasma environment. Delta doping was used to realize thin (12 nm) low-resistance layers with sheet resistance of 320 Ohm/square (mobility of 83 cm^2/Vs, integrated sheet charge of 2.4x10^14 cm^-2). A single delta-doped sheet of carriers was employed as a channel to realize a field effect transistor with current ID,MAX =292 mA/mm and transconductance gM = 27 mS/mm., Comment: 5 figures