Showing papers by "Stephen J. Pearton published in 2019"

Radiation damage effects in Ga2O3 materials and devices

Abstract: The strong bonding in wide bandgap semiconductors gives them an intrinsic radiation hardness. Their suitability for space missions or military applications, where issues of radiation tolerance are critical, is widely known. Especially β-Ga2O3, an ultra-wide bandgap material, is attracting interest for power electronics and solar-blind ultraviolet detection. Beside its superior thermal and chemical stabilities, the effects of radiation damage on Ga2O3 are of fundamental interest in space-based and some terrestrial applications. We review the effect on the material properties and device characteristics of proton, electron, X-ray, gamma ray and neutron irradiation of β-Ga2O3 electronic and optoelectronic devices under conditions relevant to low earth orbit of satellites containing these types of devices.

Editors' Choice—Hydrogen Centers in β-Ga2O3: Infrared Spectroscopy and Density Functional Theory

Abstract: β-Ga2O3 is a transparent conducting oxide with a wide bandgap (4.9 eV) whose properties are generating widespread interest. It has been found that hydrogen can play a key role in the conductivity of Ga2O3 by passivating deep defects and acting as a shallow donor. Recent vibrational spectroscopy experiments have found a dominant hydrogen center with a polarized O-H line at 3437 cm−1. These experiments along with theoretical analysis assign this line to a defect consisting of two equivalent H atoms trapped at a relaxed Ga vacancy. An expansion of this research has involved annealing treatments as well as measurements at different crystal orientations. These results have discovered a reservoir of "hidden" hydrogen in Ga2O3 whose identification involves a variety of hydrogen centers associated with the Ga vacancy, as well as other possible species.

Vertical geometry 33.2 A, 4.8 MW cm2 Ga2O3 field-plated Schottky rectifier arrays

Abstract: The performance of arrays consisting of 21 β-Ga2O3 field-plated rectifiers fabricated on thick epitaxial layers (n-type carrier concentration ∼1.6 × 1016 cm−3) grown on conducting substrates (carrier concentration 3 × 1019 cm−3) is reported. We show that by interconnecting the output of 21 smaller (0.4 × 0.4 mm2 to 1 × 1 mm2, total area 0.09 cm2) individual rectifiers using e-beam deposited Au, we can achieve a high total forward output current of 33.2 A, at 4.25 V in the single-sweep voltage mode, and a low forward turn-on voltage of 2.9 V (defined at 100 A cm−2) and maintain a reverse breakdown voltage of 240 V (defined at 1 μA cm−2). The current density was 376 A cm−2, and the on-state resistance was 0.012 Ω cm2. The total forward current was 10 A at 1.9 V and 22 A at 3 V. The power figure-of-merit for the array, VB2/RON, was 4.8 MW cm−2, with a reverse recovery time of individual rectifiers of 32 ns. The on/off ratio of the rectifier array was in the range of 105–1010 for +1 V/−1 to −100 V.

Operation Up to 500 °C of Al 0.85 Ga 0.15 N/Al 0.7 Ga 0.3 N High Electron Mobility Transistors

Abstract: AlGaN channel high electron mobility transistors (HEMTs) are the potential next step after GaN channel HEMTs, as the high aluminum content channel leads to an ultra-wide bandgap, higher breakdown field, and improved high temperature operation. Al0.85Ga0.15N/Al0.7Ga0.3N (85/70) HEMTs were operated up to 500 °C in ambient causing only 58% reduction of dc current relative to 25 °C measurement. The low gate leakage current contributed to high gate voltage operation up to +10 V under Vds = 10 V, with $\text{I}_{\mathrm{ ON}}/\text{I}_{\mathrm{ OFF}}$ ratios of $> 2 \times 10^{11}$ and 3 $\times \,\,10^{6}$ at 25 and 500 °C, respectively. Gate-lag measurements at 100 kHz and 10% duty cycle were ideal and only slight loss of pulsed current at high gate voltages was observed. Low interfacial defects give rise to high quality pulsed characteristics and a low subthreshold swing value of 80 mV/dec at room temperature. Herein is an analysis of AlGaN-channel HEMTs and their potential future for high power and high temperature applications.

Damage Recovery and Dopant Diffusion in Si and Sn Ion Implanted β-Ga2O3

Abstract: 1U.S. Naval Research Laboratory, Washington, DC 20375, USA 2Department of Chemical Engineering, University of Florida, Gainesville, Florida 32611, USA 3Department of Physics, University of Arizona, Tempe, Arizona, USA 4Department of Electrical and Computer Engineering, University of Florida, Gainesville, Florida 32611, USA 5Department of Materials Science and Engineering, University of Florida, Gainesville, Florida 32611, USA 6Tamura Corp. and Novel Crystal Technology, Sayama-city, Saitama 350-1328, Japan

Thermal Simulations of High Current β-Ga2O3 Schottky Rectifiers

Abstract: The temperature rise and distribution in large area β-Ga2O3 rectifiers is simulated using self-consistent solution of the partial differential equations governing the physics in the electrical and thermal domains with the Florida Object Oriented Device and Process simulator (FLOODS) TCAD simulator. The effect of forward voltage (0−2.5V) and power (0−5.5W) was examined for the different epitaxial layer and bulk substrate thicknesses, as well as edge termination and heat sink geometry. A higher maximum temperature is seen for the devices with thicker bulk substrates, while the effect of Joule heating was more evident in the thinner epilayer structures since the resistance decreases and the power generation increases, resulting in a higher temperature. The maximum temperature rise was ∼170K under high power conditions. The heat sink simulation results show a drop in the maximum temperature, where a Cu fin heat sink reduced the maximum temperature by 26.76%. © The Author(s) 2019. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. [DOI: 10.1149/2.0361907jss]

2D Material-Based Vertical Double Heterojunction Bipolar Transistors with High Current Amplification

Abstract: DOI: 10.1002/aelm.201800745 been applied to various types of semiconductor devices, such as lasers, solar cells, high electron mobility transistors, and heterojunction bipolar transistors (HBTs).[3–6] Notably, with a bipolar junction transistor, which is a three-terminal transistor fabricated by connecting two P–N homojunction diodes, there is a trade-off between the current gain and high-frequency ability because of these problems.[3,7] In sharp contrast, HBTs realized using the heterostructure can avoid these trade-offs and improve device performance.[8] HBTs, due to their high power efficiency, uniformity of threshold voltage, and low 1/f noise characteristics, have been widely used in high power amplifiers and high frequency switching devices.[3] It is challenging to realize high-quality hetero-interfaces in heterojunction devices, including HBTs owing to the various growth limitations involving mitigation of diffusion of both dopants and lattice elements. If present, these constraints contribute to performance degradation or even the complete loss of the benefits of incorporating the heterojunction.[3] For instance, III–V compound semiconductors such as GaAs/AlGaAs and GaN/AlGaN used in conventional heterojunction-based devices require high vacuum and high-cost growth equipment such as metalorganic vapor deposition (MOCVD) and molecular beam epitaxy (MBE). This growth is difficult to achieve when the difference of the lattice constants is too significant. Additionally, obstacles such as dislocation defects, strain caused by lattice mismatch, cross-contamination, and inter-diffusion are difficult to overcome. These problems cause device performance deterioration in the form of increased leakage current, a decrease of breakdown voltage, and an increase of recombination rate in HBT devices.[1–3] 2D materials (2DMs) have been studied in various fields over the past decade because of their excellent electrical, thermal, and mechanical properties.[9–13] In particular, heterostructures based on 2DMs have attracted interest because of their weak interlayer bonding, quantum effect, and tunneling, which are differentiated from conventional 3D bulk materials.[10,14] Weak van der Waals interactions of 2DMs can not only easily separate each layer, but can also layer materials regardless of lattice mismatch.[11] Additionally, because 2DMs have a sharp interface and no dangling bonds, heterostructures using 2DMs can solve problems such as atomic diffusion and dislocation propagation, which have been regarded as limitations of existing 3D bulk materials.[11,12] Selection of 2DMs provides The heterojunction bipolar transistor (HBT) differs from the classical homojunction bipolar junction transistor in that each emitter-base-collector layer is composed of a different semiconductor material. 2D material (2DM)based heterojunctions have attracted attention because of their wide range of fundamental physical and electrical properties. Moreover, strain-free heterostructures formed by van der Waals interaction allows true bandgap engineering regardless of the lattice constant mismatch. These characteristics make it possible to fabricate high-performance heterojunction devices such as HBTs, which have been difficult to implement in conventional epitaxy. Herein, NPN double HBTs (DHBTs) are constructed from vertically stacked 2DMs (n-MoS2/p-WSe2/n-MoS2) using dry transfer technique. The formation of the two P–N junctions, base-emitter, and base-collector junctions, in DHBTs, was experimentally observed. These NPN DHBTs composed of 2DMs showed excellent electrical characteristics with highly amplified current modulation. These results are expected to extend the application field of heterojunction electronic devices based on various 2DMs.

Comparison of Dual-Stack Dielectric Field Plates on β-Ga2O3 Schottky Rectifiers

Abstract: The effects of bilayer field plates with various dielectric (SiO2/SiNx, Al2O3/ SiNx, HfO2/ SiNx) on Ga2O3 Schottky rectifier performance were investigated. The rectifiers were fabricated on 10 μm thick, Si doped (n = 2.8 × 1016 cm−3) β-Ga2O3 epitaxial layers grown by hydride vapor phase epitaxy on Ga2O3 Sn-doped substrates (n = 4.8 × 1018 cm−3) grown by edge-defined, film-fed growth. Temperature-dependent forward current-voltage characteristics were used to extract the average Schottky barrier height of 1.14 eV ± 0.03 eV for Ni, average ideality factor of 1.02 ± 0.02, and the Richardson’s constant of 48.1 A/cm2K2. The reverse breakdown and leakage current were the two characteristics predominantly affected by the field plate dielectrics. The highest reverse breakdown reached was 730 V for rectifiers with Al2O3/ SiNx, which was significantly higher than 562 V and 401 V for rectifiers with SiO2/ SiNx and HfO2/ SiNx, respectively. The on-resistance ranged from 3.8-5.0 × 10−3 -cm2, which was dependent on diode size, with diameters from 50 to 200 μm. This led to a power figure-of-merit (VB/RON) of 140 MW-cm2. Design of the field plate is crucial in determining where reverse breakdown occurs. © The Author(s) 2019. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. [DOI: 10.1149/2.0391907jss]

Effects of InAlN underlayer on deep traps detected in near-UV InGaN/GaN single quantum well light-emitting diodes

Abstract: Two types of near-UV light-emitting diodes (LEDs) with an InGaN/GaN single quantum well (QW) differing only in the presence or absence of an underlayer (UL) consisting of an InAlN/GaN superlattice (SL) were examined. The InAlN-based ULs were previously shown to dramatically improve internal quantum efficiency of near-UV LEDs, via a decrease in the density of deep traps responsible for nonradiative recombination in the QW region. The main differences between samples with and without UL were (a) a higher compensation of Mg acceptors in the p-GaN:Mg contact layer of the sample without UL, which correlates with the presence of traps with an activation energy of 0.06 eV in the QW region, (b) the presence of deep electron traps with levels 0.6 eV below the conduction band edge (Ec) (ET1) and at Ec 0.77 eV (ET2) in the n-GaN spacer underneath the QW, and the presence of hole traps (HT1) in the QW, 0.73 eV above the valence band edge in the sample without UL (no traps could be detected in the sample with UL), and (c) a high density of deep traps with optical ionization energy close to 1.5 eV for the LEDs without UL. Irradiation with 5 MeV electrons led to a strong decrease in the electroluminescence (EL) intensity in the LEDs without UL, while for the samples with UL, such irradiation had little effect on the EL signal at high driving current, although the level of driving currents necessary to have a measurable EL signal increased by about an order of magnitude. This is despite the 5 times higher starting EL signal of the sample with UL. Irradiation also led to the appearance in the LEDs with UL of the ET1 and HT1 deep traps, but with concentration much lower than without the UL, and to a considerable increase in the Mg compensation ratio.

Diffusion of implanted Ge and Sn in β-Ga2O3

Abstract: The n-type dopants, Ge and Sn, were implanted into bulk (−201) β-Ga2O3 at multiple energies (60, 100, 200 keV) and total doses of ∼1014 cm−2 and annealed at 1100 °C for 10–120 s under either O2 or N2 ambients. The Ge-implanted samples showed almost complete recovery of the initial damage band under these conditions, with the disordered region decreasing from 130 to 17 nm after 1100 °C anneals. Fitting of secondary ion mass spectrometry profiles was used to obtain the diffusivity of both Ge and Sn, with values at 1100 °C of 1.05 × 10−11 cm s−1 for Ge and 2.7 × 10−13 cm s−1 for Sn for annealing under O2 ambients. Some of the dopant is lost to the surface during these anneals, with a surface outgas rate of 1–3 × 10−7 s−1. By sharp contrast, the redistribution of both dopants was almost completely suppressed during annealing in N2 ambients under the same conditions, showing the strong influence of point defects on dopant diffusivity of these implanted dopants in β-Ga2O3.

Valence- and Conduction-Band Offsets for Atomic-Layer-Deposited Al 2 O 3 on (010) (Al 0.14 Ga 0.86 ) 2 O 3

Abstract: The wide-bandgap ternary (AlxGa1−x)2O3 forms a heterostructure system with Ga2O3 that is attracting attention for modulation-doped field-effect transistors. The options for gate dielectric on (AlxGa1−x)2O3 are limited by the need for adequate band offsets at the heterointerface. Al2O3 deposited by atomic layer deposition (ALD) is one option due to its large bandgap (6.9 eV). We measured the valence-band offset at the Al2O3/(Al0.14Ga0.86)2O3 heterointerface using x-ray photoelectron spectroscopy (XPS). Al2O3 was deposited by ALD onto single-crystal β-(Al0.14Ga0.86)2O3 (bandgap 5.0 eV) grown by molecular beam epitaxy (MBE). The valence-band offset was determined to be 0.23 ± 0.04 eV (straddling gap, type I alignment) for ALD Al2O3 on β-(Al0.14Ga0.86)2O3. The conduction-band offset was 1.67 ± 0.30 eV, providing good electron confinement.

Optimization of Edge Termination Techniques for β-Ga2O3 Schottky Rectifiers

Abstract: To realize the potential of Gallium oxide (Ga2O3) Schottky rectifiers fabricated for high voltage and fast switching applications, various edge termination techniques to maximize the breakdown voltage (Vbr) are studied and examined via simulations using the FLOODS/FLOOPS TCAD simulator. The simulated Schottky rectifiers consist of a Si-doped (n = 1.0 × 1015 – 1.3 × 1017 cm−3) β-Ga2O3 epitaxial layer grown on Sn-doped (n = 4.8 × 1018 cm−3) Ga2O3 substrates. The optimization of field plate geometry for Schottky barrier diodes (SBD) was investigated using the device breakdown characteristics as the figure-of-merit. Various field plate dielectrics (SiO2, SiNx, Al2O3, and HfO2) were explored while the field plate structure was concurrently varied to obtain a normalized breakdown field (VNbr) of ∼3 for a step (graduated form) dielectric with Al2O3 as the dielectric. Edge termination via the formation of resistive areas at the anode contact periphery via ion (argon) implantation was also examined for the SBDs since other edge termination techniques are ineffective due to lack of p-type doping in Ga2O3. The configuration of the implanted region was investigated and a VNbr of over 5 was achieved for diodes with an unbounded resistive region and an implantation depth of 50–100 nm. © The Author(s) 2019. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. [DOI: 10.1149/2.0141912jss]

Extreme Temperature Operation of Ultra-Wide Bandgap AlGaN High Electron Mobility Transistors

Abstract: High Aluminum content channel (Al0.85Ga0.15N/ Al0.7Ga0.3N) High Electron Mobility Transistors (HEMTs) were operated from room temperature to 500°C in ambient. The devices exhibited only moderate reduction, 58%, in on-state forward current. Gate lag measurements at 100 kHz and 10% duty only showed a slight reduction in pulsed current from DC at 500°C and high gate voltages. Interfacial trap densities were $2 \times 10^{11}$ over the range 25–300°C and $3 \times 10^{12}$ cm $^{-2}$ from 300–500°C from the subthreshold swing. These low interfacial trap densities and the near ideal gate lag measurement indicate high-quality epi layers. The insulating properties of the barrier layer led to low gate induced drain leakage current of $\sim 10^{-12}$ A/mm and $\sim 10^{-8}$ A/mm at 25 and 500°C, respectively. Low leakage current was enabled by the high Schottky barrier of the Ni/Au gate, 1.1 eV and 3.3 eV at 25 and 500°C, respectively. These properties of the AlGaN channel HEMTs demonstrate their potential for high power and high temperature operation.

Valence and Conduction Band Offsets for InN and III-Nitride Ternary Alloys on (−201) Bulk β-Ga2O3

Abstract: Valence and conduction band offsets of the InN/β-Ga2O3 type-I heterojunction have been determined to be −0.55 ± 0.11 eV and −3.35 ± 0.11 eV, respectively, using X-ray photoelectron spectroscopy. The InN layers were grown using atomic layer epitaxy on (−201) oriented commercial β-Ga2O3 substrates. Combining this data with published band offsets for the GaN and AlN heterojunctions to β-Ga2O3 has allowed us to predict the band offsets for the AlGaN, AlInN, and InGaN ternary alloys to β-Ga2O3. The conduction band offsets for InGaN and AlInN to β-Ga2O3 increased for high In concentration and, similarly, the valence band offsets for AlGaN and AlInN to β-Ga2O3 decreased at high Al concentration. © The Author(s) 2019. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. [DOI: 10.1149/2.0281907jss]

60Co gamma ray damage in homoepitaxial β-Ga2O3 Schottky rectifiers

Abstract: β-Ga2O3 Schottky rectifiers consisting of thick (10 μm) epitaxial drift regions on conducting substrates are shown to have a high tolerance to 60Co gamma ray irradiation. This is due to the low carrier removal rate of <1 cm−1 for gamma rays, which contrasts to values of 300–500 cm−1 for MeV protons and alpha particles in the same rectifier structures. Changes in diode ideality factor, Schottky barrier height, on-resistance, on-off ratio, and reverse recovery time are all minimal for fluences up to 2 × 1016 cm−2 (absorbed dose of 100 kGy (Si)). These results are consistent with previous reports on gamma-irradiation of Ga2O3 metal oxide semiconductor field effect transistors (MOSFETs) where changes were ascribed to damage in the gate dielectric and not to the Ga2O3 itself.

Effect of thermal annealing for W/β-Ga2O3 Schottky diodes up to 600 °C

Abstract: The electrical and structural properties of sputter-deposited W Schottky contacts with Au overlayers on n-type Ga2O3 are found to be basically stable up to 500 °C. The reverse leakage in diode structures increases markedly (factor of 2) for higher temperature annealing of 550–600 °C. The sputter deposition process introduces near-surface damage that reduces the Schottky barrier height in the as-deposited state (0.71 eV), but this increases to 0.81 eV after a 60 s anneal at 500 °C. This is significantly lower than conventional Ni/Au (1.07 eV), but W is much more thermally stable, as evidenced by Auger electron spectroscopy of the contact and interfacial region and the minimal change in contact morphology. The contacts are used to demonstrate 1.2 A switching of forward current to −300 V reverse bias with a reverse recovery time of 100 ns and a dI/dt value of 2.14 A/μs. The on/off current ratios were ≥106 at −100 V reverse bias, and the power figure-of-merit was 14.4 MW cm−2.

Electron injection-induced effects in Si-doped β-Ga2O3

Abstract: The impact of electron injection, using 10 keV beam of a Scanning Electron Microscope, on minority carrier transport in Si-doped β-Ga2O3 was studied for temperatures ranging from room to 120°C. In-situ Electron Beam-Induced Current technique was employed to determine the diffusion length of minority holes as a function of temperature and duration of electron injection. The experiments revealed a pronounced elongation of hole diffusion length with increasing duration of injection. The activation energy, associated with the electron injection-induced elongation of the diffusion length, was determined at ∼ 74 meV and matches the previous independent studies. It was additionally discovered that an increase of the diffusion length in the regions affected by electron injection is accompanied by a simultaneous decrease of cathodoluminescence intensity. Both effects were attributed to increasing non-equilibrium hole lifetime in the valence band of β-Ga2O3 semiconductor.

Impact of electron injection and temperature on minority carrier transport in alpha-irradiated ß-Ga2O3 Schottky rectifiers

Abstract: The effect of electron injection on minority carrier transport in Si-doped β-Ga2O3 Schottky rectifiers with 18 MeV alpha particle exposure (fluences of 1012–1013 cm−2) was studied from room temperature to 120°C. Electron Beam-Induced Current technique in-situ in Scanning Electron Microscope was used to find the diffusion length of holes as a function of duration of electron injection and temperature for alpha-particle irradiated rectifiers and compared with non-irradiated reference devices. The activation energy for electron injection-induced effect on diffusion length for the alpha-particle irradiated sample was determined to be ∼ 49 meV as compared to ∼74 meV for the reference sample. The decrease in activation energy of the electron injection effect on diffusion length for irradiated sample is attributed to radiation-induced generation of additional shallow recombination centers closer to the conduction band edge. © The Author(s) 2019. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives 4.0 License (CC BY-NC-ND, http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial reuse, distribution, and reproduction in any medium, provided the original work is not changed in any way and is properly cited. For permission for commercial reuse, please email: oa@electrochem.org. [DOI: 10.1149/2.0101907jss]

Valence and conduction band offsets for sputtered AZO and ITO on (010) (Al0.14Ga0.86)2O3

Abstract: AlxGa1−x)2O3/Ga2O3 metal-oxide semiconductor field effect transistors are emerging as candidates for rf and power electronics, but a drawback is the high contact resistances on these wide bandgap semiconductors. A potential solution is to use narrower gap transparent conducting oxides such as IZO and ATO to reduce the interfacial resistance. In this paper, we report the measurement of the valence band offset of the AZO/(Al0.14Ga0.86)2O3 and ITO/(Al0.14Ga0.86)2O3 heterointerfaces using x-ray Photoelectron Spectroscopy. The single-crystal β-(Al0.14Ga0.86)2O3 was grown by molecular beam epitaxy. The bandgaps of the sputter-deposited AZO and ITO were determined by reflection electron energy loss spectroscopy to be 3.2±0.20 and 3.5±0.20 eV, respectively, while high resolution XPS data of the O 1s peak and onset of elastic losses was used to establish the (Al0.14Ga0.86)2O3 bandgap as 5.0±0.30 eV. The valence band offsets were −0.59 eV±0.10 eV and −1.18±0.20 eV, respectively, for AZO and ITO. The conduction band offsets were 1.21±0.25 eV for AZO, and 0.32±0.05 eV for ITO. Both were of the straddling gap, type I alignment on β-(Al0.14Ga0.86)2O3 and all the offsets are negative, consistent with achieving improved electron transport across the heterointerface.

Will surface effects dominate in quasi-two-dimensional gallium oxide for electronic and photonic devices?

Abstract: There is currently great interest in ultra-wide bandgap semiconductors for their applicability in power switching electronics with improved efficiency compared to current technologies and also to solar-blind UV detection. One of the most promising materials is Ga2O3, available in large area bulk crystals and as exfoliated nano-layers (nanobelts, nanomembranes, and nanosheets). One aspect of this material that has not been widely recognized is the sensitivity of its surface to environment. The goal of this brief focus article is to provide some insight into the mechanisms and defects that underlie this effect and explain inconsistencies in the literature.

Deep trap analysis in green light emitting diodes: Problems and solutions

Abstract: Some green light emitting diodes (LEDs) based on GaN/InGaN multiquantum-well (MQW) structures exhibit strong frequency and temperature dependence of capacitance and prominent changes in capacitance–voltage profiles with temperature that make it difficult to obtain reliable deep level transient spectroscopy (DLTS) measurements. DLTS performed at low probing signal frequency and with constant capacitance between the measurements by controlling applied bias mitigates these issues. This allows measurement of deep electron and hole traps in specific quantum wells (QWs) in the MQW structure. The dominant electron and hole traps detected have levels near Ec− (0.45–0.5) eV and Ev+ (0.6–0.63) eV. Their density increases significantly after aging for a long period (2120 h) at high driving current and elevated temperature. The reason for the observed anomalies in DLTS spectra of these green LEDs is the high density of states in the QWs with activation energies near 0.08, 0.12–0.14, and 0.3 eV, detected in admittance spectra, and, for the 0.08 eV and 0.3 eV, these states are likely related to defects.

Hydrogen in Ga2O3

Abstract: Hydrogen has a strong influence on the electrical properties of transparent conducting oxides where it can give rise to shallow donors and can passivate deep compensating defects. This chapter surveys the properties of the hydrogen impurity in Ga2O3. Vibrational spectroscopy has shown that the introduction of H into Ga2O3 produces a dominant hydrogen center with a strongly polarized vibrational line at 3437 cm− 1. Theory has investigated several O-H structures and assigns the 3437 cm−1 line to a defect with two equivalent H atoms that are trapped at a Ga vacancy. Annealing treatments in an H2 ambient can also produce a reservoir of “hidden” hydrogen in Ga2O3 that can be converted into other hydrogen species by annealing in an inert ambient.

Dry etching of Ga2O3

Abstract: This chapter introduces the basics of plasma-based etching of Ga2O3. It begins with a summary of different etching mechanisms and techniques and then provides a review of the literature on dry etching rates, plasma chemistries, ion-induced damage as measured by electrical, optical, and chemical means. The threshold ion energy for initiation of etching of Ga2O3 is quantified and regimes for achieving high etch rates needed for mesa formation in Ga2O3-based devices and also low damage, low rate conditions for active layer patterning are identified.

A Reconfigurable, Pulse-shaping Potentiometric Readout System for Bio-Sensing Transistors

Abstract: This paper presents a new multi-modality readout system for potentiometric electrochemical sensors. The design adopts a pulse modulation at the gate and drain of the Bio-FET sensors to reduce the effects of charge accumulation between the surface of the electrodes and the ion analytes. The adjustable duration and amplitude of stimuli signals provide flexibility for different biosensing applications and a wide range of detectable concentration. Also, an oscillator-based architecture is proposed for digitization and integration. The counting time can be adjusted to enhance the resolution of the readout system. The proposed potentiometric sensing system was tested with 0.1-10 mM Potassium Ferricyanide (K 3 [Fe(CN) 6 ]), and the results are interpreted in the micro-LCD on the board. The design offers the opportunity for a handheld medical device with fast and real-time monitoring of biomarkers and ion analytes.

Effect of Annealing on the Band Alignment of ALD SiO2 on (AlxGa1-x)2O3 for x = 0.2 - 0.65

Abstract: 1Department of Chemical Engineering, University of Florida, Gainesville, Florida 32611, USA 2Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, USA 3Universität Leipzig, Felix-Bloch-Institut für Festkörperphysik, 04103 Leipzig, Germany 4US Naval Research Laboratory, Washington DC 20375 USA 5Department of Materials Science and Engineering, University of Florida, Gainesville, Florida 32611, USA