GaAs Devices Research Articles

Aligned Semiconducting Carbon Nanotubes for Commercial Logic and RF Electronics

Carbon nanotubes are exceptional semiconductors that offer larger current densities and faster switching than conventional Si and GaAs devices, making nanotubes promising for meeting the performance and energy efficiency needs of next-generation electronics. However, the successful commercialization of carbon nanotubes necessitates the control over semiconducting purity, alignment, packing density, and scalability. The simultaneous control of these characteristics has been a major challenge preventing the integration of nanotubes in industrial electronics and the full exploitation of their electronic properties. This talk will present an overview of recent technological developments and methods that progress towards these goals.In these methods, semiconducting (purity of >99.99%) carbon nanotubes are deposited on target substrates via scalable alignment methods at room temperatures. These individual methods separately enable the deposition of quasi-aligned (±28°) nanotube arrays (~50 nanotubes µm-1) demonstrated across 100 mm substrates, highly-aligned (±6°) nanotube arrays (~100 nanotubes µm-1) demonstrated across 100 mm substrates, and the selective-area deposition of highly-aligned nanotube (±7°) arrays (~up to 250 nanotubes µm-1). The nanotube arrays with high packing density (~250 nanotubes μm-1) yield exceptional current densities of 2 mA μm-1 and transconductances of 1 mS μm-1 at VD of -0.6V. Importantly, due to the low-temperature nature of the deposition processes, these techniques offer a direct path towards the alignment of carbon nanotubes directly on Si and other materials, such as GaN or plastics, to enable high-performance 3D integrated circuits.

Statistical study of electromigration in gold interconnects

During operation of integrated circuits, electromigration gradually degrades the metallic interconnects, eventually leading to complete failure. In recent decades, electromigration has been studied mainly for the widely used aluminum and copper interconnects, however, gold interconnects used for GaAs devices also experience significant electromigration degradation. We present physics-based modeling and simulation of electromigration in gold interconnects. A comprehensive analysis of the statistical properties of electromigration failure and the influence of varying temperature and geometric properties is performed. The previously published experimental observations on the behavior of the mean failure time and the associated standard deviation are in agreement with the obtained simulation results. In particular, the simulation reproduces an 85% decrease of the standard deviation for a via surface of 31.36μm2 compared to the value for a via surface of 6.76μm2.

Enhancing Photoresponse of GaAs-Based Photodetector by Plasmon Grating Structures

Nanostructured metal–semiconductor-metal photodetectors (MSM-PDs) can assist in future high-speed communication devices for achieving high responsivity characteristics. However, such devices suffer from low responsivity due to low absorption, and the large band gap limits its detection range. Herein, we propose a GaAs-based photodetector with enhanced photoresponse by plasmonic Au-GaAs grating structure. The design of a grating structure on the surface of n-GaAs can excite a plasmon mode to enhance the photoelectric performance of photodetectors. Consequently, under 795 nm incident light irradiation, the grating hybrid detector exhibits a nearly 4.2-fold increase in photocurrent compared to the bare GaAs device. The enhanced absorption can be up to 99% and a specific responsivity of 240 mA/W is realized. These results can thus provide a potential scheme to fabricate high-performance GaAs detector for numerous applications.

Epitaxial lift-off method for GaAs solar cells with high Al content AlGaAs window layer

The epitaxial GaAs substrate lift-off (ELO) technique is widely used to produce thin film III–V semiconductor optoelectronic devices. However, the hydrofluoric (HF) acid used in the process forbids the incorporation of active AlGaAs device layers with high Al content due to its selective etching. In this work, a new ELO method is presented, which allows for the protection of AlGaAs layers against the HF acid attack. The method is used here to prepare and analyse thin film GaAs solar cells containing Al0.85Ga0.15As window layer. We employ a sacrificial GaAs buffer and device perimeter pre-processing that covers the exposed edges with back contact metals and electroplated Cu. A comparison of the epitaxially lifted GaAs solar cells with identical cells prepared by substrate etching demonstrates identical photovoltaic figures of merit and confirms the viability of the AlGaAs protection approach. In addition to applications in thin film photovoltaics, this ELO method can be applied to solid-state lasers and single-photon emitters employing AlGaAs-based Bragg reflectors, among other III–V semiconductor optoelectronic devices.

Microstructural impact on electromigration reliability of gold interconnects

Interconnect segments of gold metallization used for GaAs devices are susceptible to significant electromigration degradation and have a microstructure with thousands of grains. In this work, a complete physics-based analysis of electromigration in gold is presented. A novel approach for the numerically efficient simulation of an interconnect containing a large number of grains is introduced. By building grain compounds containing hundreds of grains and equipping them with appropriate models, the dependence of statistical failure features on the variation of geometric properties is investigated. The experimentally observed dependence of the mean failure time and the associated standard deviation of the failure times on the interconnect geometry is well reproduced by our simulations.

Thermoreflectance Study of GaAs and GaAs Passivated by the Method of Plasma Enhanced Chemical Vapor Deposition

Being the second-generation semiconductor material, GaAs is widely used in high-power devices. In this paper, a new method of multi-temperature points linear fitting for the light intensity values of the surface of GaAs collected at different temperatures, which range from 40 °C to 100 °C and the temperature rise interval is 20 °C, was used in order to obtain the thermoreflectance property. Meanwhile, the thermoreflectance property of the passivated GaAs was analyzed because the surface of GaAs is very easy to be oxidized, which will affect the performance and stability of GaAs devices. Finally, we obtained the thermoreflectance coefficient of GaAs and the passivated GaAs in visible spectrum and near-ultraviolet illumination wavelengths. The result shows that the optical response of GaAs was changed by the presence of the passivation layer significantly because of the interference effects. The study solves the problem of selecting the appropriate illumination wavelength in the study of the thermoreflectance property of GaAs. Therefore, the research is of great significance for accurate temperature measurement of GaAs semiconductor power devices.

Precise prediction of optical behaviour of mechanically stressed edge emitting GaAs devices

The presence of a thermally annealed metallization layer on top of a GaAs slab waveguide proofed to be of strong impact on the optical device behavior. Induced by the stress on the chip the elasto-optical effect imprinted a strong variation on the refractive index that led to anti-guiding and guiding effects. In order to enable precise prediction of the optical behavior we present a 3D mechanical device simulation which provides detailed insights to the overall stress state. The results are then used in a 2D in-house developed optical simulation that allows precise analysis of the microscopic optical behavior. Therefore, the accumulated stress effects are represented by an effective temperature difference between semiconductor and metallization, which allows a strong simplification of the model setup. The results are validated by comparison to the experimental derived data. As the simulation proves to be highly accurate, the stress load on the device can be calculated vice versa from the optical behavior.

Response testing of Schottky-barrier GaAs detectors with alpha particles

The development of new radiation detectors for harsh environments relies on the study of different materials and processes. In this work Gallium arsenide Schottky-barrier detectors were produced by thin film deposition on 500 μm thick GaAs wafers. Several tests of enclosure were made, and best results were obtained using commercial SSB detector fixture. Testing with NIM electronics and 241 Am alpha-particle source were made to obtain the characteristics of produced detectors. Simulations have shown that GaAs devices are resistant to ion radiation, however signal-to-noise ratio must be improved.

(110)-Oriented GaAs Devices and Spalling as a Platform for Low-Cost III-V Photovoltaics

We demonstrate the growth of GaAs solar cells by hydride vapor phase epitaxy (HVPE) on epi-ready and previously spalled (110) GaAs wafers as an advance towards a potentially low-cost (110)-based device platform. Controlled spalling offers a fracture-based path to substrate cost amortization, enabling device exfoliation and substrate reuse, but the faceted surface generated during the spalling of (100)-oriented GaAs presents hurdles to direct regrowth of subsequent devices. Spalling of (110) substrates instead eliminates faceting by aligning the substrate surface with the predominant crystal cleavage plane. III–V epitaxy of solar cells is significantly less developed on (110)-oriented substrates, however. Here, we develop (110)-based GaAs solar cells grown by HVPE on epi-ready substrates, demonstrating equal performance to devices grown on the more standard (100) orientation. We also characterize the surface of spalled, (110)-oriented substrates, revealing flat terraces separated by steps with sub-micron-scale height on average. Finally, we present an initial device grown on a previously spalled surface without additional surface re-preparation with nearly 16% efficiency under a simulated AM1.5G spectrum. Together, these results provide preliminary evidence of a potentially low-cost path to enable terrestrial III–V photovoltaics via the (110) substrate orientation.

Synchrotron Radiation Study of Gain, Noise, and Collection Efficiency of GaAs SAM-APDs with Staircase Structure.

In hard X-ray applications that require high detection efficiency and short response times, such as synchrotron radiation-based Mössbauer absorption spectroscopy and time-resolved fluorescence or photon beam position monitoring, III–V-compound semiconductors, and dedicated alloys offer some advantages over the Si-based technologies traditionally used in solid-state photodetectors. Amongst them, gallium arsenide (GaAs) is one of the most valuable materials thanks to its unique characteristics. At the same time, implementing charge-multiplication mechanisms within the sensor may become of critical importance in cases where the photogenerated signal needs an intrinsic amplification before being acquired by the front-end electronics, such as in the case of a very weak photon flux or when single-photon detection is required. Some GaAs-based avalanche photodiodes (APDs) were grown by a molecular beam epitaxy to fulfill these needs; by means of band gap engineering, we realised devices with separate absorption and multiplication region(s) (SAM), the latter featuring a so-called staircase structure to reduce the multiplication noise. This work reports on the experimental characterisations of gain, noise, and charge collection efficiencies of three series of GaAs APDs featuring different thicknesses of the absorption regions. These devices have been developed to investigate the role of such thicknesses and the presence of traps or defects at the metal–semiconductor interfaces responsible for charge loss, in order to lay the groundwork for the future development of very thick GaAs devices (thicker than 100 m) for hard X-rays. Several measurements were carried out on such devices with both lasers and synchrotron light sources, inducing photon absorption with X-ray microbeams at variable and controlled depths. In this way, we verified both the role of the thickness of the absorption region in the collection efficiency and the possibility of using the APDs without reaching the punch-through voltage, thus preventing the noise induced by charge multiplication in the absorption region. These devices, with thicknesses suitable for soft X-ray detection, have also shown good characteristics in terms of internal amplification and reduction of multiplication noise, in line with numerical simulations.

Indentation fracture toughness of semiconducting gallium arsenide at elevated temperatures

In this study, the temperature evolution of the fracture toughness in single-crystal gallium arsenide (GaAs) was investigated on the (001) plane using Vickers indentation. The highest temperature considered was 95 °C, corresponding to the typical maximum operating temperature of common GaAs semiconductor devices. Experimental results showed a decrease in hardness and an increase in toughness between 25 and 95 °C. GaAs cleavage planes were mostly composed of {110} and {100}, and predominantly aligned with the indenter’s diagonal. Measured crack lengths were used to calculate the fracture toughness. Interestingly, the size of the primary cracks on {110} was found to be unaffected by temperature, while higher temperatures led to an increased formation of secondary {001} cracks and 〈110〉 slip. An Arrhenius-type model was found to describe the observed temperature dependence of the fracture toughness. This improved understanding of the mechanism underlying the mechanical properties of GaAs during fracture is particularly useful for the failure analysis of GaAs semiconductor devices, and highlights the importance of selecting appropriate crystallographic orientations if failure in GaAs devices is to be avoided.

Wide bandgap semiconductor conversion devices for radioisotope microbatteries

Five mesa p+-i-n+ photodiodes (each of 0.126 mm2 area) were investigated as conversion devices for X-ray-voltaics, in order to understand the comparative effects between different semiconductor materials, device structures, and X-ray incident power, and to explore them for use in future radioisotope microbatteries. Three semiconductor materials (AlInP, InGaP, and GaAs) and three i layer thicknesses of one material, AlInP (2 μm, 6 μm, and 10 μm), were investigated under the illumination of various controlled X-ray incident powers. The highest short circuit current was achieved with the GaAs device due to its thickest active layer and highest linear absorption coefficients at the most numerous incident X-ray photon energies (Mo Kα at 17.48 keV; Mo Kβ at 19.6 keV). The highest open circuit voltage was achieved with the 10 μm AlInP device due to its widest bandgap (cf. InGaP and GaAs) and its highest short circuit current (cf. the 2 μm and the 6 μm AlInP devices). The greatest output X-ray power was recorded with the InGaP device due to its highest fill factor (i.e. relatively low series and high shunt resistance) compared to the rest of the devices, although the GaAs device had the highest theoretical output X-ray power. A method for selecting the most suitable semiconductor material and device structure of conversion devices for radioisotope microbatteries (for exhibiting the highest power output) is presented considering the incident X-ray spectrum, while highlighting the importance of non-ideal device effects (reduced charge collection efficiency, increased series resistance, and reduced shunt resistance).

Analysis on Influence of Hydrogen Content Exceeding Standard in GaAs Device

Aiming at the problem of hydrogen content exceeding the standard in GaAs device, the influence mechanism of hydrogen content exceeding the standard on the device is analyzed, the failure model of hydrogen content exceeding the standard in GaAs device in engineering is given, the source of hydrogen is analyzed, and the protective measures of hydrogen content exceeding the standard are given. It is of certain guiding significance for future engineering application.

FAPbBr3 perovskite quantum dots as a multifunctional luminescent-downshifting passivation layer for GaAs solar cells

Solar cells based on GaAs often include a wide-bandgap semiconductor as a window layer to improve surface passivation. Such devices often have poor photon-to-electron conversion efficiency at higher photon energies due to parasitic absorption. In this article, we deposit FAPbBr3 perovskite quantum dots on the AlInP window layer of a GaAs thin-film solar cell to improve the external quantum efficiency (EQE) across its entire absorption range, resulting in an 18% relative enhancement of the short-circuit current density. Luminescent downshifting from the quantum dots to the GaAs device contributes to a large effective enhancement of the internal quantum efficiency (IQE) at shorter wavelengths. Additionally, improved surface passivation of the window layer results in a 14–16% broadband increase of the IQE. These mechanisms combined with increased overall photon collection (antireflective effects) results in a doubling of the EQE in the ultraviolet region of the solar spectrum. Our results show a promising application of perovskite nanocrystals to improve the performance of well-established thin-film solar cell technologies.

Proton Radiation Hardness of Perovskite Solar Cells Utilizing a Mesoporous Carbon Electrode

When designing spacefaring vehicles and orbital instrumentation, the onboard systems such as microelectronics and solar cells require shielding to protect them from degradation brought on by collisions with high‐energy particles. Perovskite solar cells (PSCs) have been shown to be much more radiation stable than Si and GaAs devices, while also providing the ability to be fabricated on flexible substrates. However, even PSCs have their limits, with higher fluences being a cause of degradation. Herein, a novel solution utilizing a screen‐printed, mesoporous carbon electrode to act bi‐functionally as an encapsulate and the electrode is presented. It is demonstrated that the carbon electrode PSCs can withstand proton irradiation up to 1 × 1015 protons cm−2 at 150 KeV with negligible losses (<0.07%) in power conversion efficiency. The 12 μm thick electrode acts as efficient shielding for the perovskite embedded in the mesoporous TiO2. Through Raman and photoluminescence spectroscopy, results suggest that the structural properties of the perovskite and carbon remain intact. Simulations of the device structure show that superior radiation protection comes in conjunction with good device performance. This work highlights the potential of using a carbon electrode for future space electronics which is not limited to only solar cells.

Design and development of a coaxial cryogenic probe for precision measurements of the quantum Hall effect in the AC regime

<p class="Abstract"><span lang="EN-US">The quantum Hall effect is the basis for the realisation of the resistance and impedance units in the International System of units since 2019. This paper describes a cryogenic probe that allows to set graphene Hall devices in quantisation conditions in a helium bath (4.2 K) and magnetic fields up to 6 T, to perform precision measurements in the AC regime with impedance bridges. The probe has a full coaxial wiring, isolated from the probe structure, and holds the device in a TO-8 socket. First, characterization experiments are reported on a GaAs device, showing quantisation at 5.5 T. <span>In the AC regime, <em>multiple-series</em> connections will be employed to minimize the residual error, quantified by electrical modelling of the probe</span>.</span></p>

A nanowire optical nanocavity for broadband enhancement of spontaneous emission

To deliver an optimal performance for photonic quantum technologies, semiconductor quantum dots should be integrated in a carefully designed photonic structure. Here, we introduce a nanowire optical nanocavity designed for free-space emission. Thanks to its ultrasmall mode volume, this simple structure offers a large acceleration of spontaneous emission (predicted Purcell factor of 6.3) that is maintained over a 30-nm bandwidth. In addition, a dielectric screening effect strongly suppresses the emission into the 3D continuum of radiation modes. The fraction of spontaneous emission funneled into the cavity mode reaches 0.98 at resonance and exceeds 0.95 over a 100-nm spectral range. Close-to-optimal collection efficiency is maintained over an equivalent bandwidth and reaches a predicted value of 0.54 at resonance for a first lens with a numerical aperture (NA) of 0.75. As a first experimental demonstration of this concept, we fabricate an Au–SiO2–GaAs device embedding isolated InAs quantum dots. We measure a maximal acceleration of spontaneous emission by a factor as large as 5.6 and a bright quantum dot emission (collection efficiency of 0.35 into NA = 0.75). This nanowire cavity constitutes a promising building block to realize advanced sources of quantum light for a broad range of material systems.

Characteristics of Avalanche Charge Domain in High-Power GaAs Devices

The formation of avalanche charge domain in high-power GaAs device has been studied numerically. According to the numerical simulation results of the distribution of electric field in the bulk of the device, the variation rules of peak electric field within the domain and the domain width with the bias electric field, the carrier concentration, and the device length are obtained, respectively, and by the comparison of the variation rules with and without considering carrier impact ionization, the effect of the carrier impact ionization on the peak electric field and the domain width have been obtained. It shows that 1) the peak electric field is mainly determined by the bias electric field, the carrier concentration and the device length, and the domain width is mainly determined by the carrier concentration and the device length; 2) the carrier impact ionization and avalanche multiplication have a significant effect on the peak electric field and domain width; and 3) the value of the peak electric field and domain width are closely related to the position of domain in the direction of domain motion. Based on the variation of peak electric field and domain width, the formation of avalanche charge domain is discussed. Our results can deepen the understanding of breakover mechanism of GaAs devices and contribute to the optimization of GaAs devices performance.

Impact of Channel Thickness on the Performance of GaAs and GaSb DG-JLMOSFETs: An Atomistic Tight Binding Based Evaluation

In this paper, the performance of GaAs and GaSb based sub-10 nm double-gate junctionless metal-oxide-semiconductor field-effect transistors (DG-JLMOSFETs) have been studied for high-performance switching applications. The quantum transmitting boundary method (QTBM) has been considered for electron transport, and the band structures are accounted for sp3d5s* tight-binding modeling. The channel thickness, t <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ch</sub> is varied from 1.7 to 4.7 nm to evaluate the device figure of merits (FOMs). The thinner channel’s device shows a lower OFF-state current, while the ticker channel device allows a higher ON-state current. The threshold voltage is approximately 0.4 V for GaAs DG-JLMOSFETs with t <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ch</sub> = 1.7 nm, whereas it reduces to ~0.05 V for that of t <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ch</sub> = 4.7 nm. Similar characteristics have been shown in GaSb devices. Besides, a significant impact of t <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ch</sub> on the subthreshold swing (SS) and drain-induced barrier lowering (DIBL) is found in GaSb DG-JLMOSFETs compared with those of GaAs devices. The devices show a higher leakage-power dissipation in both channel materials and low-intrinsic delay for thicker t <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ch</sub> due to a substantial amount of energy drop. The above results indicate that III-V-based DG-JLMOSFETs are very promising for next-generation high-performance switching technology.

Time-domain photocurrent spectroscopy based on a common-path birefringent interferometer.

We present diffraction-limited photocurrent (PC) microscopy in the visible spectral range based on broadband excitation and an inherently phase-stable common-path interferometer. The excellent path-length stability guarantees high accuracy without the need for active feedback or post-processing of the interferograms. We illustrate the capabilities of the setup by recording PC spectra of a bulk GaAs device and compare the results to optical transmission data.