Selective Area Growth Research Articles

Selective Area Growth of GaN Nanowire: Partial Pressures and Temperature as the Key Growth Parameters

Selective area growth of Ga-polar GaN nanowires by metal organic chemical vapor deposition provides a path to achieve arrays of uniform nanowires with controllable dimensions. A systematic investigation on the growth parameters of GaN nanowires demonstrates that although a low V/III ratio and low precursor flows are necessary, V/III ratio is not a sufficient parameter to determine the morphology of GaN nanowires. Partial pressures of the constituent gases, on the other hand, can be used as a single parameter, at a particular growth temperature, to explain the resulting morphology. By correlating the partial pressures of precursors and H2 in the carrier gas with the morphology of the nanowires, we can then determine the flow rates for precursors and hence the range of V/III ratios required for achieving the growth of GaN nanowires.

Guest Editorial Introduction to the Special Issue on Semiconductor Optoelectronic Materials and Devices

This Special Issue of the IEEE Journal of Quantum Electronics on Semiconductor Optoelectronic Materials and Devices is dedicated to Prof. P. Daniel Dapkus and the impact he has had on the development of metal-organic chemical vapor deposition (MOCVD) for the growth and manufacture of advanced photonic devices. Prof. Dapkus has focused his career activities on the research and development of photonic materials and devices including semiconductor lasers, LEDs, solar cells, and detectors. While at Rockwell International, he led the group that demonstrated the potential and viability of MOCVD as the preferred technology for creating and manufacturing photonic devices. Prof. Dapkus, along with his colleagues Prof. Dupuis, Dr. H. Manasevit, and Prof. J. J. Coleman are widely considered to be the leading pioneers in the development of the MOCVD technique. Dapkus’ group at Rockwell International was the first to report lasing in AlGaAs/GaAs double heterostructures at room temperature in 1977. This work along with their demonstration of multiple quantum well laser diodes in 1978 has led to MOCVD becoming the dominant technique for the production of laser diodes and LEDs, along with other key photonic devices. As a Professor at USC, Dapkus’ lab investigated MOCVD fundamental growth mechanisms and selective area growth employing MOCVD. His lab made pioneering contributions to the technology of long-distance fiber-optic lasers, ultra-low-threshold datacom lasers, vertical cavity surface-emitting lasers, and photonic integrated circuits. In particular this work led to strained quaternary quantum wells became the preferred design in 1.3- and 1.55- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \textrm {m}$ </tex-math></inline-formula> laser diodes. The MOCVD technology and the quantum well material designs that were demonstrated with it now are dominant in the fabrication of devices for fiber-optic systems, data communications, facial recognition, space solar cells, solid-state lighting, and cell phone amplifiers.

Fabrication and evaluation of rib-waveguide-type wavelength conversion devices using GaN-QPM crystals

A GaN crystal comprises two polar structures along the c-axis direction, and functions as a quasi-phase-matching (QPM) crystal by fabricating a periodic inversion structure. We fabricated GaN-QPM crystals to design rib-waveguide-type devices for achieving highly efficient wavelength conversion. The QPM period required for wavelength conversion was calculated in the design phase of the device structure. GaN-QPM crystals with the obtained period were fabricated using double-polarity selective-area growth (DP-SAG). The GaN-QPM crystal was then used to fabricate a second-harmonic generation (SHG) device with a rib waveguide structure. Optical measurements revealed that the device achieved wavelength conversion from 840 to 420 nm. Further, the SHG device exhibited a wavelength conversion efficiency of 1.5 × 10–4% W−1. These results indicated that GaN-QPM crystals fabricated by DP-SAG can be used for wavelength conversion.

Photodetector Arrays Based on MBE‐Grown GaSe/Graphene Heterostructure

AbstractA selective area growth of hexagonal GaSe on prepatterned graphene substrate and fabrication of a photodetector array is reported. The GaSe film is grown on the graphene substrates using a molecular beam epitaxy system and characterized for structural and morphological properties using X‐ray diffraction, Raman, and atomic force microscopy techniques. Preliminary observations indicate the growth of hexagonal GaSe layers along (001) direction on graphene film under certain optimum growth conditions. Subsequently, GaSe‐based Schottky diode photodetectors are fabricated in a single‐element and 16 × 16 crossbar array geometries. Current–voltage characteristics of the diodes show a rectifying behavior with a turn‐on voltage and a low leakage current of ≈2 V and ≈20 nA, respectively. Photoresponse characteristics of the diode are investigated by measuring wavelength‐dependent spectral response and temporal photocurrent response under illumination of different lights, including 532 nm laser and white light, with varied incident intensities. The spectral responsivity of the detector is found to be as high as 98 A W–1 at a wavelength of 500 nm with a turning‐on profile corresponding to the band edge of GaSe. The photo mapping capability of the detector array is also demonstrated in this report.

Selective area growth of β-Ga2O3 by HCl-based halide vapor phase epitaxy

We demonstrated selective area growth of β-Ga2O3 by HCl-based halide vapor phase epitaxy on SiO2-masked (001) and (010) β-Ga2O3 substrates. Perfect growth selectivity was achieved under the presence of HCl etching gas in addition to the growth precursors. In both substrate cases, (100) facet dominated the grown shapes owing to their smallest surface energy density. High-aspect-ratio structures having (100) sidewall facets were observed for the stripe windows along [010] and [001] directions on the (001) and (010) substrates, respectively. These structures may be applicable to trenches and fins used for β-Ga2O3-based power devices.

Selective Growth of Energy-Band-Controllable In1−xGaxAsyP1−y Submicron Wires in V-Shaped Trench on Si

The In1−xGaxAsyP1−y submicron wires with adjustable wavelengths directly grown by metalorganic chemical vapor deposition on a V-groove-patterned Si (001) substrate are reported in this paper. To ensure the material quality, aspect ratio trapping and selective area growth methods are used. By changing the parameters in the epitaxy process, we realize the adjustment of the material energy band of In1−xGaxAsyP1−y submicron wires. By further optimizing the growth conditions, we realize high-quality submicron wires. The morphology of the submicron wires is characterized by scanning electron microscopy and transmission electron microscopy. Through high-resolution X-ray diffraction measurement, it is disclosed that the lattice of the optimized In1−xGaxAsyP1−y part matches that of InP. A PL spectrum test shows that the PL spectrum peak is from 1260 nm to 1340 nm. The In1−xGaxAsyP1−y can be used as a well material or barrier material in a quantum well, which would promote the development of silicon-based lasers.

Selective-Area Epitaxy of InGaAsP Buffer Multilayer for In-Plane InAs Nanowire Integration.

In order to use III–V compound semiconductors as active channel materials in advanced electronic and quantum devices, it is important to achieve a good epitaxial growth on silicon substrates. As a first step toward this, we report on the selective-area growth of GaP/InGaP/InP/InAsP buffer layer nanotemplates on GaP substrates which are closely lattice-matched to silicon, suitable for the integration of in-plane InAs nanowires. Scanning electron microscopy reveals a perfect surface selectivity and uniform layer growth inside 150 and 200 nm large SiO2 mask openings. Compositional and structural characterization of the optimized structure performed by transmission electron microscopy shows the evolution of the major facet planes and allows a strain distribution analysis. Chemically uniform layers with well-defined heterointerfaces are obtained, and the topmost InAs layer is free from any dislocation. Our study demonstrates that a growth sequence of thin layers with progressively increasing lattice parameters is effective to efficiently relax the strain and eventually obtain high quality in-plane InAs nanowires on large lattice-mismatched substrates.

Selective area epitaxy of PbTe-Pb hybrid nanowires on a lattice-matched substrate

Topological quantum computing is based on braiding of Majorana zero modes encoding topological qubits. A promising candidate platform for Majorana zero modes is semiconductor-superconductor hybrid nanowires. The realization of topological qubits and braiding operations requires scalable and disorder-free nanowire networks. Selective area growth of in-plane InAs and InSb nanowires, together with shadow-wall growth of superconductor structures, have demonstrated this scalability by achieving various network structures. However, the noticeable lattice mismatch at the nanowire-substrate interface, acting as a disorder source, imposes a serious obstacle along with this roadmap. Here, combining selective area and shadow-wall growth, we demonstrate the fabrication of PbTe-Pb hybrid nanowires - another potentially promising Majorana system - on a nearly perfectly lattice-matched substrate CdTe, all done in one molecular beam epitaxy chamber. Transmission electron microscopy shows the single-crystal nature of the PbTe nanowire and its atomically sharp and clean interfaces to the CdTe substrate and the Pb overlayer, without noticeable inter-diffusion or strain. The nearly ideal interface condition, together with the strong screening of charge impurities due to the large dielectric constant of PbTe, hold promise towards a clean nanowire system to study Majorana zero modes and topological quantum computing.

Red InGaN micro-light-emitting diodes (&amp;gt;620 nm) with a peak external quantum efficiency of 4.5% using an epitaxial tunnel junction contact

We present efficient red InGaN 60 × 60 μm2 micro-light-emitting diodes (μLEDs) with an epitaxial tunnel junction (TJ) contact. The TJ was grown by metal-organic chemical vapor deposition using selective area growth. The red TJ μLEDs show a uniform electroluminescence. At a low current density of 1 A/cm2, the emission peak wavelength is 623 nm with a full-width half maximum of 47 nm. The peak external quantum efficiency (EQE) measured in an integrating sphere is as high as 4.5%. These results suggest a significant progress in exploring high efficiency InGaN red μLEDs using TJ technology.

Doubling the mobility of InAs/InGaAs selective area grown nanowires

Selective area growth (SAG) of nanowires and networks promise a route toward scalable electronics, photonics, and quantum devices based on III-V semiconductor materials. The potential of high-mobility SAG nanowires however is not yet fully realised, since interfacial roughness, misfit dislocations at the nanowire/substrate interface and nonuniform composition due to material intermixing all scatter electrons. Here, we explore SAG of highly lattice-mismatched InAs nanowires on insulating GaAs(001) substrates and address these key challenges. Atomically smooth nanowire/substrate interfaces are achieved with the use of atomic hydrogen (a-H) as an alternative to conventional thermal annealing for the native oxide removal. The problem of high lattice mismatch is addressed through an ${\mathrm{In}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$ buffer layer introduced between the InAs transport channel and the GaAs substrate. The Ga-In material intermixing observed in both the buffer layer and the channel is inhibited via careful tuning of the growth temperature. Performing scanning transmission electron microscopy and x-ray diffraction analysis along with low-temperature transport measurements we show that optimized In-rich buffer layers promote high-quality InAs transport channels with the field-effect electron mobility over 10 000 ${\mathrm{cm}}^{2}$ ${\mathrm{V}}^{\ensuremath{-}1}$ ${\mathrm{s}}^{\ensuremath{-}1}$. This is twice as high as for nonoptimized samples and among the highest reported for InAs selective area grown nanostructures.

Disk-Shaped GaN Quantum Dots Embedded in AlN Nanowires for Room-Temperature Single-Photon Emitters Applicable to Quantum Information Technology

We demonstrate an optically pumped single-photon emitter operating at room temperature based on disk-shaped GaN/AlN quantum dots embedded in the nanowire (dot-in-wire) structure, which can act as an optical source for future quantum information technologies. The disk-like geometry of the quantum dot (QD) leads to well-defined strain distribution and controllable optical properties of the QD structure, which is revealed by theoretical calculations using a continuous elasticity model. Site-controlled GaN/AlN dot-in-wires are grown by selective area growth on prepatterned Ti/N-polar AlN/Si substrates using molecular beam epitaxy. The internal quantum efficiency of GaN QDs is 31.1%, and their photoluminescence (PL) wavelengths are in good agreement with the calculation. Measured by a micro-PL spectroscopy integrated with a Hanbury-Brown and Twiss setup, the second-order correlation at zero time delay (g(2)(0)) reaches 0.19 at room temperature for the site-controlled GaN/AlN dot-in-wires. Our work provides a promising approach to realize high-performance single-photon emission devices on-demand for application in quantum information technology.

Integration of Topological Insulator Josephson Junctions in Superconducting Qubit Circuits.

The integration of semiconductor Josephson junctions (JJs) in superconducting quantum circuits provides a versatile platform for hybrid qubits and offers a powerful way to probe exotic quasiparticle excitations. Recent proposals for using circuit quantum electrodynamics (cQED) to detect topological superconductivity motivate the integration of novel topological materials in such circuits. Here, we report on the realization of superconducting transmon qubits implemented with (Bi0.06Sb0.94)2Te3 topological insulator (TI) JJs using ultrahigh vacuum fabrication techniques. Microwave losses on our substrates, which host monolithically integrated hardmasks used for the selective area growth of TI nanostructures, imply microsecond limits to relaxation times and, thus, their compatibility with strong-coupling cQED. We use the cavity-qubit interaction to show that the Josephson energy of TI-based transmons scales with their JJ dimensions and demonstrate qubit control as well as temporal quantum coherence. Our results pave the way for advanced investigations of topological materials in both novel Josephson and topological qubits.

Selective Area Growth of GaN Using Polycrystalline γ-Alumina as a Mask for Discrete Micro-GaN Array

Selective Area Growth of GaN Using Polycrystalline γ-Alumina as a Mask for Discrete Micro-GaN Array

Theory of MBE Growth of Nanowires on Reflecting Substrates

Selective area growth (SAG) of III-V nanowires (NWs) by molecular beam epitaxy (MBE) and related epitaxy techniques offer several advantages over growth on unpatterned substrates. Here, an analytic model for the total flux of group III atoms impinging NWs is presented, which accounts for specular re-emission from the mask surface and the shadowing effect in the absence of surface diffusion from the substrate. An expression is given for the shadowing length of NWs corresponding to the full shadowing of the mask. Axial and radial NW growths are considered in different stages, including the stage of purely axial growth, intermediate stage with radial growth, and asymptotic stage, where the NWs receive the maximum flux determined by the array pitch. The model provides good fits with the data obtained for different vapor–liquid–solid and catalyst-free III-V NWs.

A New Strategy for Selective Area Growth of Highly Uniform InGaAs/InP Multiple Quantum Well Nanowire Arrays for Optoelectronic Device Applications (Adv. Funct. Mater. 3/2022)

Infrared Photodetectors In article number 2103057, Ziyuan Li, Lan Fu, and co-workers develop a new crystal facet engineering strategy to achieve epitaxial growth of highly uniform InGaAs/InP multiple quantum well nanowire arrays. This leads to the demonstration of a low threshold room temperature nanowire laser and broadband infrared photodetector with high responsivity and fast response time, promising for optical communication applications.

Selective-Area Growth of Gan and Algan Nanowires on N-Polar Gan Templates with 4° Miscut by Plasma-Assisted Molecular Beam Epitaxy

Selective-Area Growth of Gan and Algan Nanowires on N-Polar Gan Templates with 4° Miscut by Plasma-Assisted Molecular Beam Epitaxy

AlGaInAs Multi-Quantum Well Lasers on Silicon-on-Insulator Photonic Integrated Circuits Based on InP-Seed-Bonding and Epitaxial Regrowth

The tremendous demand for low-cost, low-consumption and high-capacity optical transmitters in data centers challenges the current InP-photonics platform. The use of silicon (Si) photonics platform to fabricate photonic integrated circuits (PICs) is a promising approach for low-cost large-scale fabrication considering the CMOS-technology maturity and scalability. However, Si itself cannot provide an efficient emitting light source due to its indirect bandgap. Therefore, the integration of III-V semiconductors on Si wafers allows us to benefit from the III-V emitting properties combined with benefits offered by the Si photonics platform. Direct epitaxy of InP-based materials on 300 mm Si wafers is the most promising approach to reduce the costs. However, the differences between InP and Si in terms of lattice mismatch, thermal coefficients and polarity inducing defects are challenging issues to overcome. III-V/Si hetero-integration platform by wafer-bonding is the most mature integration scheme. However, no additional epitaxial regrowth steps are implemented after the bonding step. Considering the much larger epitaxial toolkit available in the conventional monolithic InP platform, where several epitaxial steps are often implemented, this represents a significant limitation. In this paper, we review an advanced integration scheme of AlGaInAs-based laser sources on Si wafers by bonding a thin InP seed on which further regrowth steps are implemented. A 3 µm-thick AlGaInAs-based MutiQuantum Wells (MQW) laser structure was grown onto on InP-SiO2/Si (InPoSi) wafer and compared to the same structure grown on InP wafer as a reference. The 400 ppm thermal strain on the structure grown on InPoSi, induced by the difference of coefficient of thermal expansion between InP and Si, was assessed at growth temperature. We also showed that this structure demonstrates laser performance similar to the ones obtained for the same structure grown on InP. Therefore, no material degradation was observed in spite of the thermal strain. Then, we developed the Selective Area Growth (SAG) technique to grow multi-wavelength laser sources from a single growth step on InPoSi. A 155 nm-wide spectral range from 1515 nm to 1670 nm was achieved. Furthermore, an AlGaInAs MQW-based laser source was successfully grown on InP-SOI wafers and efficiently coupled to Si-photonic DBR cavities. Altogether, the regrowth on InP-SOI wafers holds great promises to combine the best from the III-V monolithic platform combined with the possibilities offered by the Si photonics circuitry via efficient light-coupling.

Effects of activation method and temperature to III-nitride micro-light-emitting diodes with tunnel junction contacts grown by metalorganic chemical vapor deposition

The optical and electrical characteristics of InGaN blue and green micro-light-emitting diodes (μLEDs) with GaN tunnel junction (TJ) contacts grown by metalorganic chemical vapor deposition (MOCVD) were compared at different activation temperatures among three activation methods from the literature, namely, sidewall activation, selective area growth (SAG), and chemical treatment before sidewall activation. The devices with chemical treatment before activation resulted in uniform electroluminescence and higher light output power, compared to the devices with sidewall activation and SAG. Moreover, the green μLEDs showed greater optical degradation at elevated activation temperatures, whereas the blue μLEDs yielded trivial difference with activation temperatures from 670 to 790 °C. The 5 × 5 μm2 devices with chemical treatment before activation and SAG yielded almost identical voltage at 20 A/cm2, and the voltage penalty significantly decreased with activation temperature in the case of devices with sidewall activation. The devices with chemical treatment before activation resulted in higher external quantum efficiency (EQE) and wall-plug efficiency (WPE) in low current density range compared to the devices with SAG. The enhancements in EQE and WPE were observed in different μLED sizes, suggesting that chemical treatment before sidewall activation enables the use of TJ contacts grown by MOCVD and is advantageous for applications that require high brightness and efficiency.

Fabrication and optical characterization of GaN quasi-phase matching crystal by double polarity selective area growth in metal organic vapor phase epitaxy

The fabrication of ultra-violet (UV) second-harmonic generation (SHG) (UV-SHG) devices requires GaN quasi-phase matching (GaN-QPM) crystals with periodically arranged polar GaN. For fabricating GaN-QPM crystals, the double polarity selective area growth (DP-SAG) using carbon mask technique is employed. However, the growth of narrow (2–4 [Formula: see text]m) pitch pattern GaN-QPM crystals, which is necessary for UV-SHG devices, has not been reported using this technique. Herein, we report the successful fabrication of 4 [Formula: see text]m pitch pattern GaN-QPM. We fabricated a thick GaN-QPM crystal at the optimized V/III ratio. Through optical characterization, we observed SHG generation from the GaN-QPM crystal fabricated using DP-SAG.

Electrical Properties of Selective-Area-Grown Superconductor-Semiconductor Hybrid Structures on Silicon

We present a superconductor-semiconductor material system that is both scalable and monolithically integrated on a silicon substrate. It uses selective area growth of Al-InAs hybrid structures on a planar III-V buffer layer, grown directly on a high resistivity silicon substrate. We characterized the electrical properties of this material system at millikelvin temperatures and observed a high average field-effect mobility of $\mu \approx 3200\,\mathrm{cm^2/Vs}$ for the InAs channel, and a hard induced superconducting gap. Josephson junctions exhibited a high interface transmission, $\mathcal{T} \approx 0.75 $, gate voltage tunable switching current with a product of critical current and normal state resistance, $I_{\mathrm{C}}R_{\mathrm{N}} \approx 83\,\mathrm{\mu V}$, and signatures of multiple Andreev reflections. These results pave the way for scalable and high coherent gate voltage tunable transmon devices and other superconductor-semiconductor hybrids fabricated directly on silicon.