James S. Speck
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View article: Evidence for Ga clusters in β-Ga2O3 from Raman spectroscopy and density functional theory
Evidence for Ga clusters in β-Ga2O3 from Raman spectroscopy and density functional theory Open
Monoclinic gallium oxide (β-Ga2O3) single crystals have a Raman mode at ∼250 cm−1 that is strongly correlated with free-electron density. Prior work attributed this peak to an electronic excitation of a shallow donor impurity band. However…
View article: Multi-fin β -Ga 2 O 3 Vertical FinFET with Interfin Field Oxide Exhibiting a Breakdown Voltage of 1.8kV and Power Figure of Merit of 1GW/cm 2
Multi-fin β -Ga 2 O 3 Vertical FinFET with Interfin Field Oxide Exhibiting a Breakdown Voltage of 1.8kV and Power Figure of Merit of 1GW/cm 2 Open
View article: Nanoscale imaging of reduced forward bias at V-pits in green-emitting nitride LEDs
Nanoscale imaging of reduced forward bias at V-pits in green-emitting nitride LEDs Open
Record wall-plug efficiencies in long-wavelength, nitride light-emitting diodes (LEDs) have recently been achieved in devices containing high V-pit densities. Numerical modeling suggests this may be due to improved electrical efficiencies …
View article: Effects of Epitaxial Layer Thickness on Heavy Ion-Induced Single-Event Burnout in Vertical β-Ga₂O₃ Schottky Barrier Diodes
Effects of Epitaxial Layer Thickness on Heavy Ion-Induced Single-Event Burnout in Vertical β-Ga₂O₃ Schottky Barrier Diodes Open
View article: Impact of threading dislocations on the V-defect assisted lateral carrier injection and recombination in InGaN quantum well LEDs
Impact of threading dislocations on the V-defect assisted lateral carrier injection and recombination in InGaN quantum well LEDs Open
The nonuniform hole distribution between InGaN quantum wells (QWs) of light emitting diodes (LEDs) has a negative impact on LED efficiency. The uniformity can be increased by using lateral hole injection through sidewalls of V-defects, whi…
View article: Origin of reduced efficiency in GaN-based micro-LEDs studied by scanning near-field optical microscopy
Origin of reduced efficiency in GaN-based micro-LEDs studied by scanning near-field optical microscopy Open
The quantum efficiency of micro-light emitting diodes (micro-LEDs) is lower than that of large area LEDs. This efficiency reduction is typically attributed to the nonradiative Shockley–Read–Hall recombination at the surface defects and cur…
View article: Trap-assisted Auger-Meitner recombination in GaN <i>p-i-n</i> diodes
Trap-assisted Auger-Meitner recombination in GaN <i>p-i-n</i> diodes Open
Most properties of semiconductor devices are dominated by shallow impurities. However, deep defects often play an important role, for instance, in recombination processes or high field transport. While a variety of techniques are available…
View article: 10.4% external quantum efficiency 294 nm UV LEDs at 20 A/cm<sup>2</sup> with a fully transparent tunnel junction
10.4% external quantum efficiency 294 nm UV LEDs at 20 A/cm<sup>2</sup> with a fully transparent tunnel junction Open
We report on the successful demonstration of an all metalorganic chemical vapor deposition (MOCVD) grown fully transparent tunnel junction (TJ) germicidal UV LED, resulting from the use of a lightly doped n - -AlGaN contact layer enabling …
View article: Increasing light extraction efficiency for UV LEDs with a low coverage p-GaN hole injection layer
Increasing light extraction efficiency for UV LEDs with a low coverage p-GaN hole injection layer Open
We report on the use of ultrathin low-coverage p-GaN hole injection islands on the top surface to improve the light extraction in UV LEDs, resulting in world-record UVB AlGaN UV LEDs emitting at 300 and 310 nm. With the optimization of the…
View article: The Influence of V-Defects, Leakage, and Random Alloy Fluctuations on the Carrier Transport in Red InGaN MQW LEDs
The Influence of V-Defects, Leakage, and Random Alloy Fluctuations on the Carrier Transport in Red InGaN MQW LEDs Open
Red InGaN-based light-emitting diodes (LEDs) exhibit lower internal quantum efficiencies (IQEs) than violet, blue, and green InGaN LEDs due to a reduction in radiative recombination rates relative to non-radiative recombination rates as th…
View article: Volumetric carrier injection in InGaN quantum well light emitting diodes
Volumetric carrier injection in InGaN quantum well light emitting diodes Open
InGaN/GaN quantum well (QW) light emitting diodes (LEDs) are essential components of solid-state lighting and displays. However, the efficiency of long wavelength (green to red) devices is inferior to that of blue LEDs. To a large degree, …
View article: Investigation of the cesium activation of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><mml:mrow><mml:mi>Ga</mml:mi><mml:mi mathvariant="normal">N</mml:mi></mml:mrow></mml:math> photocathodes by low-energy electron microscopy
Investigation of the cesium activation of photocathodes by low-energy electron microscopy Open
Low-energy electron microscopy (LEEM) was performed on p-GaN samples during in situ cesium deposition. LEEM images of electron reflectivity recorded as a function of the incident electron energy at different Cs coverages allowed to spatial…
View article: Properties of V-defect injectors in long wavelength GaN LEDs studied by near-field electro- and photoluminescence
Properties of V-defect injectors in long wavelength GaN LEDs studied by near-field electro- and photoluminescence Open
The efficiency of multiple quantum well (QW) light emitting diodes (LEDs) to a large degree depends on uniformity of hole distribution between the QWs. Typically, transport between the QWs takes place via carrier capture into and thermioni…
View article: Carrier diffusion in long wavelength InGaN quantum well LEDs after injection through V-defects
Carrier diffusion in long wavelength InGaN quantum well LEDs after injection through V-defects Open
The efficiency of operation of GaN-based light emitting diodes (LEDs) to a large degree relies on realization of a uniform hole distribution between multiple quantum wells (QWs) of the active region. Since the direct thermionic transport b…
View article: Pure edge-dislocation half-loops in low-temperature <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><mml:mrow><mml:mi>Ga</mml:mi><mml:mi mathvariant="normal">N</mml:mi></mml:mrow></mml:math> for V-defect formation
Pure edge-dislocation half-loops in low-temperature for V-defect formation Open
Lateral injection of carriers through semipolar crystallographic planes into c-plane QWs is one of the new frontiers in $\mathrm{III}$-$\mathrm{N}$ light-emitting diodes (LEDs), especially for long wavelengths. Strategic use of V-defects h…
View article: III-nitride m-plane violet narrow ridge edge-emitting laser diodes with sidewall passivation using atomic layer deposition
III-nitride m-plane violet narrow ridge edge-emitting laser diodes with sidewall passivation using atomic layer deposition Open
A novel deep-ridge laser structure with atomic-layer deposition (ALD) sidewall passivation was proposed that enhances the optical characteristics of 8-µm ridge width III-nitride violet lasers on freestanding m -plane GaN substrates. The in…
View article: Erratum: “Planarization of <i>p</i>-GaN surfaces on MOCVD grown V-defect engineered GaN-based LEDs” [Appl. Phys. Lett. <b>124</b>, 172102 (2024)]
Erratum: “Planarization of <i>p</i>-GaN surfaces on MOCVD grown V-defect engineered GaN-based LEDs” [Appl. Phys. Lett. <b>124</b>, 172102 (2024)] Open
View article: Dynamics of carrier injection through V-defects in long wavelength GaN LEDs
Dynamics of carrier injection through V-defects in long wavelength GaN LEDs Open
The efficiency of high-power operation of multiple quantum well (QW) light emitting diodes (LEDs) to a large degree depends on the realization of uniform hole distribution between the QWs. In long wavelength InGaN/GaN QW LEDs, the thermion…
View article: Optical analysis of III-nitride micro-light-emitting diodes with different sidewall treatments at low current density operation
Optical analysis of III-nitride micro-light-emitting diodes with different sidewall treatments at low current density operation Open
In this work, the optical efficiency of III-nitride blue micro-LEDs ( μ LEDs) ranged from 5 × 5 to 60 × 60 μ m 2 with different sidewall treatments at low current density range was investigated. The results showed dielectric sidewall passi…
View article: Current transport mechanisms of metal/TiO2/<i>β</i>-Ga2O3 diodes
Current transport mechanisms of metal/TiO2/<i>β</i>-Ga2O3 diodes Open
β-Ga2O3 is of great interest for power electronic devices with efficiency beyond current generation Si, 4H-SiC, and GaN devices due to its large breakdown electric field of ∼8 MV/cm. However, taking advantage of this large field strength i…
View article: Injection mechanisms in a <i>III</i>-nitride light-emitting diode as seen by self-emissive electron microscopy
Injection mechanisms in a <i>III</i>-nitride light-emitting diode as seen by self-emissive electron microscopy Open
We report on the investigation of an electrically biased high efficiency green III-nitride light-emitting diode (LED) by electron emission microscopy (EEM) using a low-energy electron microscope (LEEM). The surface of the LED was activated…
View article: Experimental evidence of hole injection through V-defects in long wavelength GaN-based LEDs
Experimental evidence of hole injection through V-defects in long wavelength GaN-based LEDs Open
Hole injection through V-defect sidewalls into all quantum wells (QWs) of long wavelength GaN light emitting diodes had previously been proposed as means to increase efficiency of these devices. In this work, we directly tested the viabili…
View article: Carrier localization in III-nitride versus conventional III-V semiconductors: A study on the effects of alloy disorder using landscape theory and the Schrödinger equation
Carrier localization in III-nitride versus conventional III-V semiconductors: A study on the effects of alloy disorder using landscape theory and the Schrödinger equation Open
International audience
View article: High external quantum efficiency (6.5%) InGaN V-defect LEDs at 600 nm on patterned sapphire substrates
High external quantum efficiency (6.5%) InGaN V-defect LEDs at 600 nm on patterned sapphire substrates Open
Highly efficient long-wavelength InGaN LEDs have been a research focus in nitride LEDs for their potential applications in displays and solid-state lighting. A key breakthrough has been the use of laterally injected quantum wells via natur…
View article: Corrigendum: Importance of shallow hydrogenic dopants and material purity of ultra-wide bandgap semiconductors for vertical power electron devices (2020 <i>Semicond. Sci. Technol.</i> 35 125018)
Corrigendum: Importance of shallow hydrogenic dopants and material purity of ultra-wide bandgap semiconductors for vertical power electron devices (2020 <i>Semicond. Sci. Technol.</i> 35 125018) Open
View article: Origins of the high-energy electroluminescence peaks in long-wavelength (∼495–685 nm) InGaN light-emitting diodes
Origins of the high-energy electroluminescence peaks in long-wavelength (∼495–685 nm) InGaN light-emitting diodes Open
We investigate the unexpected high-energy electroluminescence (EL) peaks observed in long-wavelength InGaN light-emitting diodes (LEDs) with ground state emission peaks between ∼495 and 685 nm by studying the EL spectra of LEDs with varyin…
View article: Effect of Mg doping on carrier recombination in GaN
Effect of Mg doping on carrier recombination in GaN Open
Time-resolved photoluminescence measurements have been performed on Mg-doped GaN for Mg concentrations in the low- to mid-1019 cm−3. As-grown and annealed (600–675 °C) samples were studied. In the as-grown samples, the nonradiative carrier…
View article: Atomic layer etching (ALE) of III-nitrides
Atomic layer etching (ALE) of III-nitrides Open
Atomic layer etching (ALE) was performed on (Al, In, Ga)N thin films using a cyclic process of alternating Cl2 gas absorption and Ar+ ion bombardment in an inductively coupled plasma etcher system. The etch damage was characterized by comp…
View article: First‐Principles Study of Twin Boundaries and Stacking Faults in <i>β</i>‐Ga<sub>2</sub>O<sub>3</sub>
First‐Principles Study of Twin Boundaries and Stacking Faults in <i>β</i>‐Ga<sub>2</sub>O<sub>3</sub> Open
This study uses density functional theory calculations to explore the energetics and electronic structures of planar defects in monoclinic β ‐Ga 2 O 3 , including twin boundaries (TBs) and stacking faults (SFs). TBs on the (001)A, (001)B, …
View article: Steady-state junction current distribution in p-n GaN diodes measured using low-energy electron microscopy (LEEM)
Steady-state junction current distribution in p-n GaN diodes measured using low-energy electron microscopy (LEEM) Open
We report on the measurement of the lateral distribution of the junction current of an electrical biased p-n GaN diode by electron emission microscopy using a low-energy electron microscope. The vacuum level at the surface of the diode was…