2020年4月13日星期一

Effect of cavity-layer thicknesses on two-color emission in coupled multilayer cavities with InAs quantum dots

A GaAs/AlAs coupled multilayer cavity structure was grown on a (001) GaAs substrate. The top cavity contains self-assembled InAs quantum dots (QDs) as optical gain materials for two-color emission of cavity-mode light. The bottom cavity layer was grown with lateral thickness variation in the wafer to investigate the effects of the thickness difference between the two cavity layers quantitatively. The frequency difference was minimum, and the intensity ratio of the two-color emission was unity when the optical thicknesses of the two cavity layers were the same. The emission intensity ratio was explained in terms of the electric fields at the top cavity region containing the QDs.

Source:IOPscience

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2020年4月7日星期二

DH Lasers Fabricated by New III-V Semiconductor Material InAsPSb

Double heterostructure wafers composed of p-InAs0.82P0.10Sb0.08/n-InAs0.94P0.04Sb0.02/n-InAs0.82P0.12Sb0.06 were grown on (001) oriented n-InAs substrates by liquid phase epitaxy. Stripe geometry lasers were fabricated from these wafers. The emission wavelength and the threshold current density of these lasers at 77 K were 3.0 µm and about 3 kA/cm2, respectively. Their threshold current density (Jth) was quite sensitive to the ambient temperature; the characteristic temperature T0, defined as T0=ΔT/Δ In Jth was 23 K in the temperature range between 77 K and 145 K.

Source:IOPscience

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2020年3月29日星期日

Investigation of a near mid-gap trap energy level in mid-wavelength infrared InAs/GaSb type-II superlattices

In this report, we present results of an experimental investigation of a near mid-gap trap energy level in InAs10 ML/GaSb10 ML type-II superlattices. Using thermal analysis of dark current, Fourier transform photoluminescence and low-frequency noise spectroscopy, we have examined several wafers and diodes with similar period design and the same macroscopic construction. All characterization techniques gave nearly the same value of about 140 meV independent of substrate type. Additionally, photoluminescence spectra show that the transition related to the trap centre is temperature independent. The presented methodology for thermal analysis of dark current characteristics should be useful to easily estimate the position of deep energy levels in superlattice photodiodes.

Source:IOPscience

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2020年3月24日星期二

Low- and high-density InAs nanowires on Si(0 0 1) and their Raman imaging

Micro-Raman imaging along with other techniques are applied to study the morphology, structure and crystalline quality of various types of InAs nanowires (NWs). The NWs of low and high densities are formed using metal organic vapor phase epitaxy. Raman mapping is effectively used as a local probe to gain information about the structure and crystalline quality of low-density NWs where the conventional characterization techniques are not very useful. However, for high-density NWs, the image and crystalline quality obtained from the LO phonon strongly corroborate with scanning electron microscopy and x-ray diffraction (XRD) results, respectively. These low-density (104 cm−2) and high-density (108 cm−2) NWs are grown on Si(0 0 1) under various growth conditions such as catalyst-assisted and catalyst-free growth, growth on native oxide-covered and oxide-cleaned Si, grooved Si surfaces and also varying the V/III ratio and growth temperature. NWs (1 µm long and 50–100 nm wide) with high density and tapered NWs (50–80 µm long and 200–500 nm wide at the tip) with low density are formed under different growth conditions. The growth of hillock- and wire-like structures is observed under the same growth condition. Raman, XRD, scanning electron microscopy and atomic force microscopy analyses confirm that the hillocks are grown along the 〈0 0 1〉 direction, whereas the wires are grown along [1 1 0] directions in the plane of Si(0 0 1). Furthermore, the Raman analysis of these NWs confirms that the smaller NWs have much better crystalline quality (half-width of LO phonon frequency ~6 cm−1) compared to the larger NWs (half-width of LO phonon frequency ~15 cm−1) although both NWs are oriented with the Si(0 0 1) surface.

Source:IOPscience

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2020年3月18日星期三

Sub-100 nm Si nanowire and nano-sheet array formation by MacEtch using a non-lithographic InAs nanowire mask

We report a non-lithographical method for the fabrication of ultra-thin silicon (Si) nanowire (NW) and nano-sheet arrays through metal-assisted-chemical-etching (MacEtch) with gold (Au). The mask used for metal patterning is a vertical InAs NW array grown on a Si substrate via catalyst-free, strain-induced, one-dimensional heteroepitaxy. Depending on the Au evaporation angle, the shape and size of the InAs NWs are transferred to Si by Au-MacEtch as is (NWs) or in its projection (nano-sheets). The Si NWs formed have diameters in the range of ~25–95 nm, and aspect ratios as high as 250 in only 5 min etch time. The formation process is entirely free of organic chemicals, ensuring pristine Au–Si interfaces, which is one of the most critical requirements for high yield and reproducible MacEtch.

Source:IOPscience

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2020年3月11日星期三

Structural and electrical transport properties of MOVPE-grown pseudomorphic AlAs/InGaAs/InAs resonant tunneling diodes on InP substrates

We report metal–organic vapor-phase epitaxy (MOVPE) growth of pseudomorphic AlAs/InGaAs/InAs resonant tunneling diodes (RTDs) on InP substrates for the first time. X-ray diffraction (XRD) measurements and transmission electron microscopy (TEM) observations reveal that a uniform strained InAs subwell is coherently grown in the double-barrier (DB) structure. The AlAs/InGaAs/InAs RTDs exhibit excellent current–voltage characteristics with a high peak current density (JP) of around 2 × 105 A/cm2 and peak-to-valley ratio (PVR) of around 6. A comparison with control RTDs consisting of AlAs/In0.8Ga0.2As DB confirms the effectiveness of InAs subwell insertion for the improvement of PVR.

Source:IOPscience

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2020年3月5日星期四

Low Output-Conductance InAs-Channel Metal-Oxide-Semiconductor Field-Effect Transistors with SiO2 Gate Dielectrics

This study reports the development of InAs-channel MOSFETs using PECVD-deposited SiO2 gate dielectrics. Arsenic capping and desorption are applied to as-grown wafers to prevent the formation of native oxides before the gate dielectrics are then deposited. We believe that increased hole confinement in a layer structure effectively suppresses the impact ionization effect, and an output conductance as 18 mS/mm at a drain bias of 2 V is demonstrated. A 2 μm-gate-length device exhibits dc performances of IDSS = 154 mA/mm and gm = 189 mS/mm, and rf performances of fT = 14.5 GHz and fMAX = 24 GHz. The InAs-channel MOSFET has potential for application in high frequency circuit devices.

Source:IOPscience

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2020年2月25日星期二

Nanoimprint and selective-area MOVPE for growth of GaAs/InAs core/shell nanowires

We report on the technology and growth optimization of GaAs/InAs core/shell nanowires. The GaAs nanowire cores were grown selectively by metal organic vapor phase epitaxy (SA-MOVPE) on SiO2masked GaAs $(\bar {1}\bar {1}\bar {1})\mathrm{B}$ templates. These were structured by a complete thermal nanoimprint lithography process, which is presented in detail. The influence of the subsequent InAs shell growth temperature on the shell morphology and crystal structure was investigated by scanning and transmission electron microscopy in order to obtain the desired homogeneous and uniform InAs overgrowth. At the optimal growth temperature, the InAs shell adopted the morphology and crystal structure of the underlying GaAs core and was perfectly uniform.

Source:IOPscience

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2020年2月19日星期三

Rate-limiting mechanisms in high-temperature growth of catalyst-free InAs nanowires with large thermal stability

We identify the entire growth parameter space and rate-limiting mechanisms in non-catalytic InAs nanowires (NWs) grown by molecular beam epitaxy. Surprisingly huge growth temperature ranges are found with maximum temperatures close to ~600 °C upon dramatic increase of V/III ratio, exceeding by far the typical growth temperature range for catalyst-assisted InAs NWs. Based on quantitative in situ line-of-sight quadrupole mass spectrometry, we determine the rate-limiting factors in high-temperature InAs NW growth by directly monitoring the critical desorption and thermal decomposition processes of InAs NWs. Both under dynamic (growth) and static (no growth, ultra-high vacuum) conditions the (111)-oriented InAs NWs evidence excellent thermal stability at elevated temperatures even under negligible supersaturation. The rate-limiting factor for InAs NW growth is hence dominated by In desorption from the substrate surface. Closer investigation of the group-III and group-V flux dependences on growth rate reveals two apparent growth regimes, an As-rich and an In-rich regime defined by the effective As/In flux ratio, and maximum achievable growth rates of  > 6 µm h−1. The unique features of high-T growth and excellent thermal stability provide the opportunity for operation of InAs-based NW materials under caustic environment and further allow access to temperature regimes suitable for alloying non-catalytic InAs NWs with GaAs.

Source:IOPscience

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2020年2月12日星期三

Electroluminescence at 1.3 µm from InAs/GaAs quantum dots monolithically grown on Ge/Si substrate by metal organic chemical vapor deposition

We report the first demonstration of electroluminescence at 1.3 µm from InAs/GaAs quantum dots (QDs) monolithically grown on a Ge/Si substrate by metal organic chemical vapor deposition (MOCVD). High-density coalescence-free InAs/Sb:GaAs QDs emitting at 1.3 µm were obtained on a GaAs/Ge/Si wafer. The post-growth annealing of the GaAs buffer layer shows a significant improvement in the room-temperature (RT) photoluminescence (PL) intensity of QDs grown on a GaAs/Ge/Si wafer, comparable to those QDs grown on a reference GaAs substrate. Together, these results are promising for the realization of a QD laser on a Si substrate by MOCVD for silicon photonics application.

Source:IOPscience

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2020年1月20日星期一

Proper In deposition amount for on-demand epitaxy of InAs/GaAs single quantum dots*

The test-QD in-situ annealing method could surmount the critical nucleation condition of InAs/GaAs single quantum dots (SQDs) to raise the growth repeatability. Here, through many growth tests on rotating substrates, we develop a proper In deposition amount (θ) for SQD growth, according to the measured critical θ for test QD nucleation (θ c). The proper ratio θ/θ c, with a large tolerance of the variation of the real substrate temperature (T sub), is 0.964−0.971 at the edge and > 0.989 but < 0.996 in the center of a 1/4-piece semi-insulating wafer, and around 0.9709 but < 0.9714 in the center of a 1/4-piece N+ wafer as shown in the evolution of QD size and density as θ/θ c varies. Bright SQDs with spectral lines at 905 nm–935 nm nucleate at the edge and correlate with individual 7 nm–8 nm-height QDs in atomic force microscopy, among dense 1 nm–5 nm-height small QDs with a strong spectral profile around 860 nm–880 nm. The higher T sub in the center forms diluter, taller and uniform QDs, and very dilute SQDs for a proper θ/θ c: only one 7-nm-height SQD in 25 μm2. On a 2-inch (1 inch = 2.54 cm) semi-insulating wafer, by using θ/θ c = 0.961, SQDs nucleate in a circle in 22% of the whole area. More SQDs will form in the broad high-T sub region in the center by using a proper θ/θ c.

Source:IOPscience

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2020年1月13日星期一

Fabrication of two-color surface emitting device of a coupled vertical cavity structure with InAs quantum dots formed by wafer bonding

We fabricated a two-color surface emitting device of a coupled cavity structure, which is applicable to terahertz light source. GaAs/AlGaAs vertical multilayer cavity structures were grown on (001) and (113)B GaAs substrates and the coupled multilayer cavity structure was fabricated by wafer bonding them. The top cavity contains self-assembled InAs quantum dots (QDs) as optical gain materials for two-color emission of cavity-mode lights. The bonding position was optimized for the equivalent intensity of two-color emission. We formed a current injection structure, and two-color emission was observed by current injection, although no lasing was observed.

Source:IOPscience

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2020年1月7日星期二

Tuning the bandgap of InAs quantum dots by selective-area MOCVD

In-plane bandgap energy control of InAs quantum dots (QDs) grown on GaAs substrates is demonstrated using selective-area epitaxy. Transmission electron microscopy and cathodoluminescence are used for characterization of the selectively grown dots. A single-step growth of a thin InAs quantum well and InAs QDs emitting at 1010 and 1100 nm (at 77 K) on the same wafer is demonstrated. Non-uniform growth profile is reported for the selectively grown QDs in the mask openings. Surface migration of adatoms from higher order facets to (1 0 0) facets results in enhanced deposition rates closer to the edge of the openings and vapour phase diffusion of adatoms results in density variations across the openings over length scales greater than the surface migration length of the adatoms.

Source:IOPscience

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InAs on Insulator by Hydrogen Implantation and Exfoliation

InAs on insulator structures were successfully fabricated using wafer bonding and hydrogen implantation and exfoliation processes. Material was exfoliated from either a bulk InAs substrate or from a metamorphic InAs layer grown by MBE via a graded buffer layer on InP. The InAs from the bulk substrate exfoliates as a uniform planar layer with a large surface roughness, ~150 nm, which is similar to the estimated straggle. Under certain conditions, the InAs from the graded buffer layer, however, exfoliates non-uniformly, only transferring long wires of InAs that lie along a specific [110] direction. The size and spacing of these wires resemble the cross-hatch induced by the graded buffer layer growth indicating the exfoliation is influenced by dislocation strain fields. High resolution x-ray diffraction indicates that strain-free InAs is transferred in both cases, however, mosaic tilt is induced into the transferred layer by the hydrogen implantation step.


Source:IOPscience

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