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We demonstrate a superluminescent diode fabricated on a nonpolar ${m}$ -plane GaN substrate by employing a linearly tapered waveguide design. A high electrical −3dB modulation bandwidth ( $f_{\mathbf {3dB}}$ ) of 2.5 GHz at a current density of 30 kA/cm2 is achieved. The high modulation bandwidth is attributed to the shorter carrier recombination lifetime, the linear gain curve in the nonpolar ${m}$ -plane quantum wells, and the ability to operate at high current densities while effectively suppressing lasing. We derive a general expression for the −3dB bandwidth as a function of current density for SLDs using a similar approach to that for laser diodes. The −3dB bandwidth of a nonpolar superluminescent diode increases exponentially with current density. The experimental results are consistent with the derived expression for $f_{\mathbf {3dB}}$ vs . current density.

Multiphysics processes such as recombination dynamics in the active region, carrier injection and transport, and internal heating may contribute to thermal and efficiency droop in InGaN/GaN light-emitting diodes (LEDs). However, an unambiguous methodology and characterization technique to decouple these processes under electrical injection and determine their individual roles in droop phenomena is lacking. In this work, we investigate thermal and efficiency droop in electrically injected single-quantum-well InGaN/GaN LEDs by decoupling the inherent radiative efficiency, injection efficiency, carrier transport, and thermal effects using a comprehensive rate equation approach and a temperature-dependent pulsed-RF measurement technique. Determination of the inherent recombination rates in the quantum well confirms efficiency droop at high current densities is caused by a combination of strong non-radiative recombination (with temperature dependence consistent with indirect Auger) and saturation of the radiative rate. The overall reduction of efficiency at elevated temperatures (thermal droop) results from carriers shifting from the radiative process to the non-radiative processes. The rate equation approach and temperature-dependent pulsed-RF measurement technique unambiguously gives access to the true recombination dynamics in the QW and is a useful methodology to study efficiency issues in III-nitride LEDs.

We report high-voltage regrown nonpolar ${m}$ -plane p-n diodes on freestanding GaN substrates. A high blocking voltage of 540 V at ~1 mA/cm $^{\textsf {2}}$ (corresponding to an electric field of E ~ 3.35 MV/cm), turn- ON voltages between 2.9 and 3.1 V, specific on-resistance of 1.7 $\text{m}\Omega \cdot \textsf {cm}^{\textsf {2}}$ at 300 A/cm $^{\textsf {2}}$ , and a minimum ideality factor of 1.7 were obtained for the regrown diodes. Our results suggest that Si, O, and C interfacial impurity levels up to $\textsf {2}\times \textsf {10}^{\textsf {17}}$ cm $^{-\textsf {3}}$ , $\textsf {8}\times \textsf {10}^{\textsf {17}}$ cm $^{-\textsf {3}}$ , and $\textsf {1}\times \textsf {10}^{\textsf {19}}$ cm $^{-\textsf {3}}$ , respectively, at the metallurgical junction of ${m}$ -plane, p-n diodes do not result in very early breakdown in the reverse bias although the off-state leakage current in the forward bias is affected. The impact of the growth interruption/regrowth on diode performance is also investigated.

GaN-based vertical-cavity surface-emitting lasers (VCSELs) have drawn interest in recent years for their potential applications in data storage, laser printing, solid-state lighting, optical communications, sensing, and displays. Several research groups have demonstrated electrically injected GaN-based VCSELs utilizing different growth and fabrication techniques to address the many challenges associated with III-nitride materials. One such challenge is fabrication of highquality conductive epitaxial distributed Bragg reflectors (DBRs). A relatively new approach that yields high-index-contrast lattice-matched epitaxial DBRs is to introduce subwavelength air-voids (nanopores) in alternating layers of doped/undoped GaN. These nanoporous layers can be achieved by the controlled anodic electrochemical etching of highly doped n-type GaN in acids. The selective formation of the nanopores in the doped layers effectively lowers the refractive index compared to the adjacent undoped GaN layers, resulting in a refractive index difference of ~0.83, allowing high reflectance (>99%) with only ~16 pairs. Here, we will present electrically injected nonpolar m-plane GaN-based VCSELs with lattice-matched nanoporous GaN bottom DBRs and top dielectric DBRs. Lasing under pulsed operation at room temperature was observed at 409 nm with a linewidth of ~0.6 nm and a maximum output power of ~1.5 mW. The nonpolar m-plane orientation offers low transparency, high material gain, and anisotropic gain characteristics. The VCSELs were linearly polarized with a polarization ratio of ~0.94 and polarization-pinned emission along the a-direction. The mode profiles, thermal properties, and lasing yield of the VCSELs are also discussed.

We demonstrate a high-speed nonpolar ${m}$ -plane InGaN/GaN micro-scale light-emitting diode (LED) with a record electrical −3 dB modulation bandwidth of 1.5 GHz at a current density of 1 kA/cm2. A differential carrier lifetime (DLT) of 200 ps at 1 kA/cm2 was extracted using a rate-equation model. The short DLT is attributed to the high electron–hole wave function overlap in polarization-free nonpolar InGaN/GaN quantum wells, which leads to a higher spontaneous emission rate at low current densities compared to polar $c$ -plane quantum wells. LEDs with improved high-speed performance at low current densities will help to reduce power dissipation and increase efficiency in Gb/s visible-light communication systems.

We utilize a rate equation approach and RF measurement technique to study carrier dynamics in InGaN/GaN LEDs. Study of carrier dynamics aids in understanding efficiency challenges and design of high-speed, efficient micro-LEDs for visible-light communication and micro-LED display applications.

III-nitride high-speed optoelectronics are emerging for a variety of applications, including visible-light communication (VLC) in light-fidelity (Li-Fi) networks, optical communication using photonic-integrated circuits, and micro-pixel LED displays. III-nitride materials offer efficient light emission and the potential to route, modulate, and detect light on a single chip. Previous research into III-nitride optoelectronics has mainly focused on developing emitters with high efficiencies and large optical output powers, which are needed for conventional lighting and data storage applications. Here, we present the more recent development of III-nitride high-speed emitters, including planar micro-LEDs, nanowire-based micro-LEDs, and superluminescent diodes. We demonstrate record-high modulation bandwidths by growing devices on nonpolar and semipolar orientations of GaN, which are free from the polarization-related effects that limit the modulation bandwidths of $c$ -plane III-nitride. We also combine a rate equation model with an RF measurement technique to extract the carrier dynamics in the devices [1].

We investigate the impact of high-dose gamma-ray irradiation on the electrical performance of Ga-polar and N-polar GaN-based p–n diodes grown by metalorganic chemical vapor deposition. We compare the current density–voltage (J–V), capacitance–voltage (C–V), and circular transfer length method characteristics of the p–n diodes fabricated on Ga-polar and N-polar orientations before and after irradiation. The relative turn-on voltage increases for the Ga-polar diodes with an increasing irradiation dose, while it increases initially and then starts to decrease for the N-polar diodes. The p-contact total resistance increases for Ga-polar and decreases for N-polar samples, which we attribute to the formation of point defects and additional Mg activation after irradiation. The J–V characteristics of most of the tested diodes recovered over time, suggesting the changes in the J–V characteristics are temporary and potentially due to metastable occupancy of traps after irradiation. X-ray photoelectron spectroscopy and photoluminescence measurements reveal the existence of different types of initial defects and surface electronic states on Ga-polar and N-polar samples. Gallium vacancies (VGa) are dominant defects in Ga-polar samples, while nitrogen vacancies (VN) are dominant in N-polar samples. The presence of a higher concentration of surface states on Ga-polar surfaces than N-polar surfaces was confirmed by calculating the band bending and the corresponding screening effect due to opposite polarization bound charge and ionized acceptors at the surface. The difference in surface stoichiometry in these two orientations is responsible for the different behavior in electrical characteristics after gamma-ray interactions.

Steady-state photocapacitance (SSPC) was conducted on nonpolar m-plane GaN n-type Schottky diodes to evaluate the defects induced by inductively coupled plasma (ICP) dry etching in etched-and-regrown unipolar structures. An ∼10× increase in the near-midgap Ec – 1.9 eV level compared to an as-grown material was observed. Defect levels associated with regrowth without an etch were also investigated. The defects in the regrown structure (without an etch) are highly spatially localized to the regrowth interface. Subsequently, by depth profiling an etched-and-regrown sample, we show that the intensities of the defect-related SSPC features associated with dry etching depend strongly on the depth away from the regrowth interface, which is also reported previously [Nedy et al., Semicond. Sci. Technol. 30, 085019 (2015); Fang et al., Jpn. J. Appl. Phys. 42, 4207–4212 (2003); and Cao et al., IEEE Trans. Electron Devices 47, 1320–1324 (2000)]. A photoelectrochemical etching (PEC) method and a wet AZ400K treatment are also introduced to reduce the etch-induced deep levels. A significant reduction in the density of deep levels is observed in the sample that was treated with PEC etching after dry etching and prior to regrowth. An ∼2× reduction in the density of Ec – 1.9 eV level compared to a reference etched-and-regrown structure was observed upon the application of PEC etching treatment prior to the regrowth. The PEC etching method is promising for reducing defects in selective-area doping for vertical power switching structures with complex geometries [Meyers et al., J. Electron. Mater. 49, 3481–3489 (2020)].

The increasing demand for wireless data communication and popularity of solid-state lighting has prompted research into visible-light communication (VLC) systems using GaN-based light-emitting diodes (LEDs). VLC is a promising candidate for next-generation (5G and beyond) network systems. To support multi-Gb/s data rates, VLC systems will require efficient LEDs with large modulation bandwidths. Conventional lighting-class LEDs cannot achieve high-speed operation due to their large chip size, large active region volume, and phosphor-converted output. Conversely, micro-scale LEDs (micro-LEDs) offer a viable path to high-speed operation. Furthermore, conventional c-plane LEDs suffer from polarization-related electric fields, which reduce the overlap between the electron and hole wave functions and lower the carrier recombination rate. Since modulation bandwidth is proportional to the carrier recombination rate, the overlap between the wave functions should be maximized for high-speed operation. Nonpolar and semipolar orientations have significantly reduced polarization effects and wave function overlaps approaching unity. These orientations can enable high-efficiency LEDs with simultaneously large modulation bandwidths. In this work, we introduce VLC and discuss progress on the growth, fabrication, and characterization of high-speed micro-LEDs. Polar (0001), nonpolar (10-10), and semipolar (20-2-1) InGaN/GaN micro-LEDs on free-standing GaN substrates are investigated for their small-signal modulation characteristics as a function of current density, temperature, device area, and active region design. Record modulation bandwidths above 1 GHz are achieved for the nonpolar and semipolar orientations. We also present a small-signal method for determining the RC characteristics, differential carrier lifetime, carrier escape lifetime, and injection efficiency of the LEDs under electrical injection.

GaN is an attractive material for high-power electronics due to its wide bandgap and large breakdown field. Verticalgeometry devices are of interest due to their high blocking voltage and small form factor. One challenge for realizing complex vertical devices is the regrowth of low-leakage-current p-n junctions within selectively defined regions of the wafer. Presently, regrown p-n junctions exhibit higher leakage current than continuously grown p-n junctions, possibly due to impurity incorporation at the regrowth interfaces, which consist of c-plane and non-basal planes. Here, we study the interfacial impurity incorporation induced by various growth interruptions and regrowth conditions on m-plane p-n junctions on free-standing GaN substrates. The following interruption types were investigated: (1) sample in the main MOCVD chamber for 10 min, (2) sample in the MOCVD load lock for 10 min, (3) sample outside the MOCVD for 10 min, and (4) sample outside the MOCVD for one week. Regrowth after the interruptions was performed on two different samples under n-GaN and p-GaN growth conditions, respectively. Secondary ion mass spectrometry (SIMS) analysis indicated interfacial silicon spikes with concentrations ranging from 5e16 cm-3 to 2e18 cm-3 for the n-GaN growth conditions and 2e16 cm-3 to 5e18 cm-3 for the p-GaN growth conditions. Oxygen spikes with concentrations ~1e17 cm-3 were observed at the regrowth interfaces. Carbon impurity levels did not spike at the regrowth interfaces under either set of growth conditions. We have correlated the effects of these interfacial impurities with the reverse leakage current and breakdown voltage of regrown m-plane p-n junctions.

We report the fabrication and electro-optic characterization of nonpolar GaN-based superluminescent diodes with a tapered waveguide design. The devices were grown and fabricated on freestanding m-plane GaN. An electrical −3dB modulation bandwidth of 2.5 GHz is reported at the highest current density.

We demonstrate a high-speed nonpolar InGaN/GaN micro-LED with a record −3dB bandwidth of 1.5 GHz at a current density of 1 kA/cm2. The high-speed at low current density is attributed to the large electron-hole wavefunction overlap in nonpolar QWs leading to a shorter carrier lifetime.

Free-standing nonpolar GaN substrates provide an excellent platform for the fabrication of high-speed blue and green light-emitting diodes (LEDs), which are attractive for visible-light communication, plastic optical fiber communication, and short-range under water optical communication. Nonpolar LEDs on free-standing GaN exhibit a large electron-hole wave function overlap, low extended defect density, and favorable thermal properties. Here, we demonstrate high-speed nonpolar InGaN/GaN LEDs with a peak emission wavelength between 455 and 465 nm on free-standing nonpolar GaN substrates. A large frequency modulation bandwidth of 524 MHz is demonstrated at a current density of 10 kA/cm 2 .

We investigate a mechanism causing shorting of large area GaSb diodes grown on GaSb substrates using molecular beam epitaxy (MBE). The source of these shorts is determined to be large crystallographic defects on the surface of the diodes that are formed around droplets of gallium ejected from the gallium Knudsen cells during MBE. The gallium droplets cause defects in the crystal structure, and, as the epitaxy continues, the gallium is incorporated into the surrounding material. The shape of the defects is pyramidal with a central void extending from the epi-surface to the gallium core. Processing a GaSb diode with these surface defects results in the top-side contact metal migrating into the defect and shorting the diode. This prevents realization of large area diodes that are critical to applications such as photovoltaics and detectors. The diodes in this study are electrically characterized and the defect formation mechanism is investigated using cross-section transmission electron microscopy and electron dispersive spectroscopy.

Superior electronic material properties of GaN semiconductors compared to Si will enable the foundational diodes and transistors for the next revolution in power management technology. To date, high-performance GaN diodes have been demonstrated with breakdown voltages near 5 kV and specific on-resistances of less than 5 mΩ-cm2 [1]. However, a viable GaN vertical power switching transistor is the missing element necessary to realize advanced power management systems utilizing GaN. While GaN transistors are now ubiquitous in RF systems, their lateral device architecture inherently limits these devices to niche applications in power systems. Rather, high-voltage systems rely on vertical device architectures where current flow is normal to the semiconductor surface. Vertical power electronics devices such as junction field effect transistors (JFETs) require selective areas of p-type semiconductor surrounded by lightly-doped n-type semiconductor. For Si power devices, p-type regions are implanted in n-type drift regions to create p/n junctions that act as a gate and pinch-off current. Ion implantation presents challenges in GaN and requires specialized equipment and processes, including high-pressure and high-temperature annealing, for dopant activation [2]. Our previous work using metal-organic chemical vapor deposition (MOCVD) where p-type GaN was regrown on a lightly-doped, non-etched n-type drift layer demonstrated planar p/n diodes with the same electrical performance as continuously-grown devices. However, when dry-etching processes are used before the regrowth of the p-type GaN layer, as would be needed to define a regrown area, planar diodes demonstrate higher forward and reverse leakage currents, and lower breakdown voltage. Deep Level Optical Spectroscopy (DLOS) was used to identify the source of the higher forward and reverse leakage currents observed in diodes with p-type anodes re-grown on inductively coupled plasma (ICP) dry-etched n-type drift layers. We will report DLOS studies of various diode structures that show the formation of a mid-gap trap located ~ 1.7 eV below the conduction band in dry-etched, lightly doped (Nd-Na = 2x1016 cm-3) drift layers. We also will show that various wet-chemical treatments of the dry-etched n-type drift layer prior to p-anode regrowth results in diodes with 1 to 2 orders of magnitude lower reverse leakage current. DLOS measurements of regrown diodes showed a 3 times reduction in the density of the mid-gap deep level trap following wet-chemical treatment. These studies establish the connection between high reverse and forward leakage currents with residual damage caused by dry-etching and that this damage can be mitigated by with wet-chemical treatments prior to regrowth of the p-anode. The information, data, or work presented herein was funded in part by the Advanced Research Projects Agency – Energy (ARPA-E), U.S. Department of Energy under the PNDIODES programs directed by Dr. Isik Kizilyalli. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA-0003525. H. Ohta et al., J. J. Appl. Phys., 57, 04FG09 (2018). T.J. Anderson et al., Elec. Lett., 50(3), 197 (2014).

We demonstrate the first electrically injected nonpolar m-plane GaN-based vertical-cavity surface-emitting lasers (VCSELs) with lattice-matched nanoporous bottom DBRs. Lasing under pulsed operation at room temperature was observed near 409 nm with a linewidth of ~0.6 nm and a maximum output power of ~1.5 mW. The VCSELs were linearly polarized and polarization-locked in the a-direction, with a polarization ratio of 0.94. The high polarization ratio and polarization pinning reveal that the optical scattering from the nanoporous DBRs is negligible. A high characteristic temperature of 357 K resulted from the slightly negative offset between the peak gain and cavity mode wavelengths.

The increasing demand for wireless data communication and popularity of solid-state lighting has prompted research into visible-light communication (VLC) systems using GaN-based light-emitting diodes (LEDs). VLC is a promising candidate for next-generation (5G and beyond) light-fidelity (Li-Fi) network systems. To support multi-Gb/s data rates, VLC systems will require efficient LEDs with large modulation bandwidths. Conventional lighting-class LEDs cannot achieve high-speed operation due to their large chip size, large active region volume, and phosphor-converted output. Conversely, micro-scale LEDs (micro-LEDs) offer a viable path to high-speed operation due to their lower parasitic capacitance and ability for operation at high current densities where the carrier lifetime is significantly reduced. Furthermore, conventional c-plane LEDs suffer from polarization-related electric fields, which reduce the overlap between the electron and hole wave functions and lower the carrier recombination rate. Since modulation bandwidth is proportional to the carrier recombination rate (inversely proportional to the carrier lifetime), the overlap between the wave functions should be maximized for high-speed operation. Nonpolar and semipolar orientations have significantly reduced polarization effects and wave function overlaps approaching unity. These orientations can enable high-efficiency LEDs with simultaneously large modulation bandwidths, especially at relatively low current densities. In this work, we introduce VLC and discuss progress on the growth, fabrication, and characterization of high-speed micro-LEDs. Polar (0001), nonpolar (1010), and semipolar (2021) InGaN/GaN micro-LEDs on free-standing GaN substrates are investigated for their small-signal modulation characteristics as a function of current density, temperature, device area, and active region design. We demonstrate that the modulation bandwidths are well correlated with the wave function overlap in the active region by examining the orientation-dependence of the bandwidth. Record modulation bandwidths for GaN-based LEDs above 1 GHz are achieved for the nonpolar and semipolar orientations. We also show the modulation characteristics of an electrically injected nanowire-based LED, which achieves a modulation bandwidth of 1.2 GHz. Finally, we present a small-signal modeling method for determining the RC characteristics, differential carrier lifetime, carrier escape lifetime, and injection efficiency of the LEDs under electrical injection and discuss the results in the context of efficiency droop. Figure 1: Bandwidth vs. current density for the nonpolar LEDs (open black triangles), semipolar LED (open blue circles), and polar c-plane LED (open green squares) compared to other reported polar c-plane LEDs on sapphire or with a flip-chip design and compared to semipolar (1122) LEDs. The bandwidth characteristics for a nanowire-based LED are also included. Also shown are the crystal orientations used in the orientation-dependent bandwidth study. Figure 1

We extract the injection efficiency as a function of current density in single-quantum-well semipolar ( 20 2 ¯ 1 ¯) InGaN/GaN light-emitting diodes (LEDs) using small-signal RF measurements and rate equation analysis of the dominant carrier mechanisms. The rate equations are used to derive a small-signal equivalent circuit that yields expressions for the modulation response and the input impedance of the LED. Simultaneous fitting of the modulation response and the input impedance of the circuit to the measured modulation response and the input impedance of the LED gives the differential carrier lifetime, the net differential carrier escape time from the active region, and the differential recombination lifetime in the cladding layers. The extracted lifetimes are used to calculate the injection efficiency of the LED at various current densities. Carrier leakage from the active region results in an injection efficiency below one at low current densities. At high current densities, the injection efficiency approaches one due to the higher recombination rate in the quantum well (QW) and the lower carrier leakage. Analysis of the lifetimes shows that the higher recombination rate in the QW results in a slower increase in the carrier population in the QW compared to that in the cladding layers. However, the recombination current in the QW is generally higher than that in the cladding, leading to high injection efficiency at high current densities. The data are consistent with a Coulomb-enhanced capture process. The high injection efficiency obtained at high current densities rules out injection-related mechanisms as the primary cause of efficiency droop in semipolar ( 20 2 ¯ 1 ¯) InGaN/GaN LEDs.

InGaN/GaN light-emitting diodes (LEDs) with large modulation bandwidths are desirable for visible-light communication. Along with modulation speed, the consideration of the internal quantum efficiency (IQE) under operating conditions is also important. Here, we report the modulation characteristics of semipolar (202¯1¯) InGaN/GaN (LEDs) with single-quantum well (SQW) and multiple-quantum-well (MQW) active regions grown on free-standing semipolar GaN substrates with peak internal quantum efficiencies (IQEs) of 0.93 and 0.73, respectively. The MQW LEDs exhibit on average about 40–80% higher modulation bandwidth, reaching 1.5 GHz at 13 kA/cm2, but about 27% lower peak IQE than the SQW LEDs. We extract the differential carrier lifetimes (DLTs), RC parasitics, and carrier escape lifetimes and discuss their role in the bandwidth and IQE characteristics. A coulomb-enhanced capture process is shown to rapidly reduce the DLT of the MQW LED at high current densities. Auger recombination is also shown to play little role in increasing the speed of the LEDs. Finally, we investigate the trade-offs between the bandwidth and efficiency and introduce the bandwidth-IQE product as a potential figure of merit for optimizing speed and efficiency in InGaN/GaN LEDs.

High-speed InGaN/GaN blue light-emitting diodes (LEDs) are needed for future gigabit-per-second visible-light communication systems. Large LED modulation bandwidths are typically achieved at high current densities, with reports close to 1 GHz bandwidth at current densities ranging from 5 to 10 kA/cm2. However, the internal quantum efficiency (IQE) of InGaN/GaN LEDs is quite low at high current densities due to the well-known efficiency droop phenomenon. Here, we show experimentally that nonpolar and semipolar orientations of GaN enable higher modulation bandwidths at low current densities where the IQE is expected to be higher and power dissipation is lower. We experimentally compare the modulation bandwidth vs. current density for LEDs on nonpolar (101¯0), semipolar (202¯1¯), and polar 0001 orientations. In agreement with wavefunction overlap considerations, the experimental results indicate a higher modulation bandwidth for the nonpolar and semipolar LEDs, especially at relatively low current densities....

GaSb thermophotovoltaic cells fabricated using Molecular Beam Epitaxy (MBE) and ion implantation techniques are studied. Challenges including different defect formation mechanisms using MBE and ion-induced defects using ion implantation were investigated by cross-sectional Transmission Electron Microscopy (XTEM), X-Ray Diffraction spectroscopy (XRD) and Scanning Electron Microscopy (SEM). For MBE grown TPVs, several approaches were used to suppress defects, including substrate preparation and using different MBE reactors. For ion-implanted TPVs, different implant doses and energies were tested to minimize the crystal damage and various Rapid Thermal Anneal (RTA) process recipes were studied to maximize the crystal recovery. Large area TPV cells with 1 × 1 cm dimensions were fabricated using these techniques, then electrically and optically characterized. Ideality factors and dark saturation currents were measured and compared for various TPVs.

We report the carrier dynamics and recombination coefficients in single-quantum-well semipolar $(20\bar 2\bar 1)$ InGaN/GaN light-emitting diodes emitting at 440 nm with 93% peak internal quantum efficiency. The differential carrier lifetime is analyzed for various injection current densities from 5 $A/cm^2$ to 10 $kA/cm^2$, and the corresponding carrier densities are obtained. The coupling of internal quantum efficiency and differential carrier lifetime vs injected carrier density ($n$) enables the separation of the radiative and nonradiative recombination lifetimes and the extraction of the Shockley-Read-Hall (SRH) nonradiative ($A$), radiative ($B$), and Auger ($C$) recombination coefficients and their $n$-dependency considering the saturation of the SRH recombination rate and phase-space filling. The results indicate a three to four-fold higher $A$ and a nearly two-fold higher $B_0$ for this semipolar orientation compared to that of $c$-plane reported using a similar approach [A. David and M. J. Grundmann, Appl. Phys. Lett. 96, 103504 (2010)]. In addition, the carrier density in semipolar $(20\bar 2\bar 1)$ is found to be lower than the carrier density in $c$-plane for a given current density, which is important for suppressing efficiency droop. The semipolar LED also shows a two-fold lower $C_0$ compared to $c$-plane, which is consistent with the lower relative efficiency droop for the semipolar LED (57% vs. 69%). The lower carrier density, higher $B_0$ coefficient, and lower $C_0$ (Auger) coefficient are directly responsible for the high efficiency and low efficiency droop reported in semipolar $(20\bar 2\bar 1)$ LEDs., The text is 13 pages and includes 5 figures

This work describes a small-signal microwave method for determining the differential carrier lifetime and transport effects in electrically injected InGaN/GaN light-emitting diodes (LEDs). By considering the carrier diffusion, capture, thermionic escape, and recombination, the rate equations are used to derive an equivalent small-signal electrical circuit for the LEDs, from which expressions for the input impedance and modulation response are obtained. The expressions are simultaneously fit to the experimental data for the input impedance and modulation response for nonpolar InGaN/GaN micro-LEDs on free-standing GaN substrates. The fittings are used to extract the transport related circuit parameters and differential carrier lifetimes. The dependence of the parameters on the device diameter and current density is reported. We also derive approximations for the modulation response under low and high injection levels and show that the transport of carriers affects the modulation response of the device, espe...

Ultra-low resistance ohmic contacts on n-GaSb with specific transfer resistances down to 0.12 Ω-mm and specific contact resistances of ~1.1e-6 Ω-cm2 have been successfully fabricated on semi-insulating (SI) GaAs substrates using the Interfacial Misfit Dislocation (IMF) technique. The IMF technique enables epitaxial growth of GaSb layers on semi-insulating GaAs substrates resulting in vertical current confinement not possible on unintentionally ~ 1e17 cm-3 p-doped bulk GaSb. Results for low resistance ohmic contacts using NiGeAu, PdGeAu, GeAuNi and GeAuPd metallizations for various temperatures are reported. The low annealing temperature of NiGeAu and PdGeAu metallizations show promising results, but the lifetime of a device with these contacts have not yet been studied.

Low resistance ohmic contacts have been successfully fabr icated on n-GaSb layers grown by MBE on semi-insulating (SI) GaAs substrates using the Interfacial Misfit Dislocation (IMF) technique. Although intended for photovoltaic applications, the results are applicable to many antimonide-based devices. The IMF technique enables the growth of epitaxial GaSb layers on semi-insulating GaAs substrates resulting in vertical current confinement not possible on unintentionally doped ~ 1e17 cm -3 p-doped bulk GaSb. Results for low resistance ohmic contacts using NiGeAu, PdGeAu, GeAuNi and GeAuPd metallizations for various temp eratures are reported. Specifi c transfer resistances down to 0.12 Ÿ -mm and specific contact resistances of < 2e-6 Ÿ -cm 2 have been observed. Keywords: Ohmic contacts, GaSb, GaAs, Interfacial Misfit Di slocation, TLM pattern, Sp ecific contact resistance 1. INTRODUCTION Antimonide semiconductors such as GaSb and InSb have a great potential to provide heterojunction structures that absorb or emit light in the longer wavelength IR regime. The GaSb lattice parameter is matched with various ternary and quaternary III-V compounds covering bandgaps from 0.3 eV to 1.58 eV

Low resistance ohmic contacts were fabricated on n-type GaSb grown by molecular beam epitaxy. N-type GaSb epilayers with different doping concentrations and thicknesses were fabricated and studied in order to investigate the current transport mechanism between the metal contacts and the semiconductor. Different metallization schemes were implemented to achieve the lowest possible contact resistance. Rapid thermal annealing was performed at various temperatures to achieve the optimal gold penetration into the GaSb epilayers for low resistance. Ohmic contact fabrication and electrical characterization are discussed in detail. The microstructure analysis of the semiconductor and metal contact interfaces was performed using cross-section transmission electron microscopy and energy dispersive spectroscopy. Specific contact resistances as low as 3 × 10−6 Ω cm2 were obtained.

Characteristics of ion implantation induced damage in GaSb, and its removal by rapid thermal annealing, are investigated by cross-sectional transmission electron microscopy. Rapid thermal annealing (RTA) has been implemented on implanted GaSb for various temperatures and durations with the semiconductor capped, which avoids Sb out-diffusion and Ga agglomeration during the process. The RTA damage induced in the GaSb wafer was studied by scanning electron microscopy and energy dispersive x-ray spectroscopy. The results of the microscopy study were then used to optimize the RTA recipe and the Si3N4 capping layer thickness to achieve doping activation while minimizing crystalline damage. Results indicate a lattice quality that is close to pristine GaSb for samples annealed at 600 °C for 10 s using 260 nm thick Si3N4 capping layer. Secondary ion mass spectrometry measurement indicates that the implanted Be does not migrate in the GaSb at the used annealing temperature. Finally, electrical characteristics of diodes fabricated from the implanted material are presented that exhibit low series resistance and high shunt resistance suitable for photovoltaic applications.

Ultra low resistance ohmic contacts are fabricated on n-GaSb grown by molecular beam epitaxy. Different doping concentrations and n-GaSb thicknesses are studied to understand the tunneling transport mechanism between the metal contacts and the semiconductor. Different contact metallization and anneal process windows are investigated to achieve optimal penetration depth of Au in GaSb for low resistances. The fabrication, electrical characterization, and microstructure analysis of the metal-semiconductor interfaces created during ohmic contact formation are discussed. The characterization techniques include cross-sectional transmission electron microscopy and energy dispersive spectroscopy. Specific transfer resistances down to 0.1 Ω mm and specific contact resistances of 1 × 10−6 Ω cm2 are observed.