2017年11月19日星期日

Dry etching of deep air holes in GaAs/AlGaAs-based epi-wafer having InAs quantum dots for fabrication of photonic crystal laser

Abstract

Photonic crystal (PhC) structures are often fabricated on epi-wafers with a heterostructure to realize various micro- or nanophotonic devices by dry etching processes. We discuss the dry etching process for a GaAs/AlGaAs-based epi-wafer using a resist mask to fabricate a proposed PhC laser. The epi-wafer has multiple stacked layers of InAs quantum dots (QDs) with a high density of 6 × 1010 cm−2, which cause the reduction of the diameter of the etched air holes. A higher density and more stacked layers of QDs intensify the reduction effect. By enhancing the physical etching effect, the verticality of the profile of the air holes etched in the epi-wafer with a five stacked InAs QD layers is greatly improved. The results show that the improved etching conditions make it feasible to fabricate the proposed PhC laser structure.
Source:IOPscience
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2017年10月30日星期一

Structural and surface characteristics of room temperature and low temperature swift heavy ion implanted InAs and InSb wafers

Abstract

The effect of low temperature swift heavy ion (LT-SHI) implantation on InAs(1 0 0) and InSb(1 0 0) wafers have been investigated. SHI implantation was carried out with 70 MeV silicon (Si5+) ions with fluences of 1 × 1010, 1 × 1011, 1 × 1012 and 1 × 1013 ions/cm2 at room temperature (RT) and liquid nitrogen temperature (LNT). The X-ray diffraction peak intensity of the LT-SHI implanted sample increases with respect to the ion fluences, while the full width half maximum (FWHM) value decreases correspondingly with the increase of ion fluences for both InAs and InSb samples. Whereas the X-ray diffraction peak intensity decreases with respect to the increase of ion fluences for the samples implanted at RT. Scanning electron microscopy (SEM) was used in cross-sectional mode to analyze the penetration depth of silicon ions in InAs and InSb wafers. Atomic force microscopy revealed that the average surface roughness values (Rrms) of InAs and InSb samples implanted at LNT, decreased with the increase of ion fluences while an opposite effect has been observed in the case of RT implanted samples. The present study has confirmed the improvement in the structural and surface properties of InAs and InSb wafers when they are subjected to LT-SHI implantation with 70 MeV silicon (Si5+) ions.
Source:ScienceDirect
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2017年10月22日星期日

A review of thermal processing in the subsecond range: semiconductors and beyond

Abstract

Thermal processing in the subsecond range comprises modern, non-equilibrium annealing techniques which allow various material modifications at the surface without affecting the bulk. Flash lamp annealing (FLA) is one of the most diverse methods for short-time annealing with applications ranging from the classical field of semiconductor doping to the treatment of polymers and flexible substrates. It still continues to extend its use to other material classes and applications, and is becoming of interest for an increasing number of users. In this review we present a short, but comprehensive and consistent picture of the current state-of-the-art of FLA, sometimes also called pulsed light sintering. In the first part we take a closer look at the physical and technological background, namely the electrical and optical specifications of flash lamps, the resulting temperature profiles, and the corresponding implications for process-relevant parameters such as reproducibility and homogeneity. The second part briefly considers the various applications of FLA, starting with the classical task of defect minimization and ultra-shallow junction formation in Si, followed by further applications in Si technology, namely in the fields of hyperdoping, crystallization of thin amorphous films, and photovoltaics. Subsequent chapters cover the topics of doping and crystallization in Ge and silicon carbide, doping of III–V semiconductors, diluted magnetic semiconductors, III–V nanocluster synthesis in Si, annealing of transparent conductive oxides and high-k materials, nanoclusters in dielectric matrices, and the use of FLA for flexible substrates.
Source:IOPscience
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Researchers create high performance infrared camera based on type-II InAs/GaSb superlattices


Researchers at Northwestern University have created a new infrared camera based on Type-II InAs/GaSb superlattices that produces much higher resolution images than previous infrared cameras.

Created by Manijeh Razeghi, Walter P. Murphy Professor of Electrical Engineering and Computer Science, and researchers in the Center for Quantum Devices in the McCormick School of Engineering and Applied Science, the long wavelength infrared focal plane array camera provides a 16-fold increase in the number of pixels in the image and can provide  in the dark. Their results were recently published in the journal , Volume 97, Issue 19, 193505 (2010).

The goal of the research is to offer a better alternative to existing long wavelength  (LWIR) cameras, which, with their thermal imaging capabilities, are used in everything from electrical inspections to security and nighttime surveillance. Current LWIR cameras are based on mercury  (MCT) materials, but the Type-II superlattice is mercury-free, more robust, and can be deposited with better uniformity. This will significantly increase yield and reduce camera cost once the technology goes commercial.

"Not only does it prove Type-II superlattices as a viable alternative to MCT, but also it widens the field of applications for infrared cameras," Razeghi said. "The importance of this work is similar to that of the realization of mega-pixel visible cameras in the last decade, which shaped the world's favor for digital cameras."

Type-II InAs/GaSb superlattices were first invented by Nobel laureate Leo Esaki in the 1970s, but it has taken time for the material to mature. The LWIR detection mechanism relies on quantum size effects in a completely artificial layer sequence to tune the wavelength sensitivity and demonstrate high efficiency. Razeghi's group has been instrumental in pioneering the recent development of Type-II superlattices, having demonstrated the world's first Type-II–based 256×256  just a few years ago.

"Type-II is a very interesting and promising new material for infrared detection," Razeghi said. "Everything is there to support its future: the beautiful physics, the practicality of experimental realization of the material. It has just taken time to prove itself, but now, the time has come."

Tremendous obstacles, especially in the fabrication process, had to be overcome to ensure that the 1024×1024 Type-II superlattice–based camera would have equivalent performance as the previously realized 320×256 cameras. Operating at 81 K, the new camera can collect 78 percent of the light and is capable of showing temperature differences as small as 0.02° C.


Source:PHYS
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2017年9月25日星期一

Evolution of Raman spectra in n-InAs wafer with annealing temperature

Highlights

The LO Raman peaks of annealed (1 0 0) n-InAs wafers disappear with increasing annealing temperature, indicating the elimination of surface electron accumulation layers.
Amorphous In2O3 and As2O3 phases are formed at InAs surface during annealing and a thin crystalline As layer at the interface between the oxidized layer and InAs wafer is also generated.
The thickness of surface electron accumulation layers decreases with increasing annealing temperature since the amount of generated As adatoms acting as acceptor impurities increases.

Abstract

The influence of annealing temperature on the optical properties of surface electron accumulation layers in n-type (1 0 0) InAs wafers has been investigated by Raman spectroscopy. It exhibits that Raman peaks due to scattering by unscreened LO phonons disappear with increasing temperature, which indicates that the electron accumulation layer in InAs surface is eliminated by annealing. The involved mechanism was analyzed by X-ray photoelectron spectroscopy, X-ray diffraction and high-resolution transmission electron microscopy. The results show that amorphous In2O3 and As2O3 phases are formed at InAs surface during annealing and, meanwhile, a thin crystalline As layer at the interface between the oxidized layer and the wafer is also generated which leads to a decrease in thickness of the surface electron accumulation layer since As adatoms introduce acceptor type surface states.

PACS

68.47.Fg
78.30.Fs
68.35.Ja

Keywords

Surface charge accumulation layer
InAs
Annealing
Raman

Source:ScienceDirect
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2017年9月6日星期三

Wet etch methods for InAs nanowire patterning and self-aligned electrical contacts

Abstract

Advanced synthesis of semiconductor nanowires (NWs) enables their application in diverse fields, notably in chemical and electrical sensing, photovoltaics, or quantum electronic devices. In particular, indium arsenide (InAs) NWs are an ideal platform for quantum devices, e.g. they may host topological Majorana states. While the synthesis has been continously perfected, only a few techniques have been developed to tailor individual NWs after growth. Here we present three wet chemical etch methods for the post-growth morphological engineering of InAs NWs on the sub-100 nm scale. The first two methods allow the formation of self-aligned electrical contacts to etched NWs, while the third method results in conical shaped NW profiles ideal for creating smooth electrical potential gradients and shallow barriers. Low temperature experiments show that NWs with etched segments have stable transport characteristics and can serve as building blocks of quantum electronic devices. As an example we report the formation of a single electrically stable quantum dot between two etched NW segments.
Source:IOPscience
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2017年8月13日星期日

A modified gradient approach for the growth of low-density InAs quantum dot molecules by molecular beam epitaxy

Highlights

A gradient approach for low density vertically stacked quantum dots is presented.
Only for the bottom quantum dot layer Indium is deposited with a spatial gradient.
The strain field induces a gradient in quantum dot density also in the top layer.
Approach works for a narrow range of Indium amounts in the top layer.

Abstract

Two vertically stacked quantum dots that are electronically coupled, so called quantum dot molecules, are of great interest for the realization of solid state building blocks for quantum communication networks. We present a modified gradient approach to realize InAs quantum dot molecules with a low areal density so that single quantum dot molecules can be optically addressed. The individual quantum dot layers were prepared by solid source molecular beam epitaxy depositing InAs on GaAs(100). The bottom quantum dot layer has been grown without substrate rotation resulting in an In-gradient across the surface, which translated into a density gradient with low quantum dot density in a certain region of the wafer. For the top quantum dot layer, separated from the bottom quantum dot layer by a 6 nm thick GaAs barrier, various InAs amounts were deposited without an In-gradient. In spite of the absence of an In-gradient, a pronounced density gradient is observed for the top quantum dots. Even for an In-amount slightly below the critical thickness for a single dot layer, a density gradient in the top quantum dot layer, which seems to reproduce the density gradient in the bottom layer, is observed. For more or less In, respectively, deviations from this behavior occur. We suggest that the obvious influence of the bottom quantum dot layer on the growth of the top quantum dots is due to the strain field induced by the buried dots.

Keywords


A1. Nanostructures
A3. Molecular beam epitaxy
B2. Semiconducting III-V materials
B2. Semiconducting gallium arsenide
Source:ScienceDirect
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2017年8月10日星期四

PAPER Electrical transport in ion beam created InAs nanospikes

Abstract

Ion beam irradiation has previously been demonstrated as a method for creating nanowire-like semiconductor nanostructures, but no previous studies have reported on the electrical properties of those structures. In this work we describe the creation and in situ transmission electron microscopy electrical characterization of nanoscale InAs spike structures on both InAs and InP substrates fabricated using a focused ion beam erosion method. Those InAs 'nanospikes' are found to possess internal structures with varying amounts of ion damaged and single crystalline material. Nanospike electrical behavior is analyzed with respect to model electronic structures and is similar to cases of barrier limited conduction in nanowires. The different electrical responses of each nanospike are found to be the result of variation in their structure, with the conductivity of InAs nanospikes formed on InAs substrates found to increase with the degree of nanospike core crystallinity. The conductivity of InAs nanospikes formed on InP substrates does not show a dependence on core crystallinity, and may be controlled by the other internal barriers to conduction inherent in that system.
Source:IOPscience
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2017年8月1日星期二

Interruption-assisted epitaxy of faceted p-InAs on buffered GaSb for terahertz emitters

Abstract

We demonstrate molecular beam epitaxy growth of p-InAs layers on GaAs-buffered GaSb that may be suitable for terahertz applications. GaAs buffer deposition is initiated by applying growth interruption. Reflection high-energy electron diffraction shows that GaAs growth proceeds to a quasi-two-dimensional growth mode. The scheme allows growth of a p-InAs layer 600 nm to 1.0 µm thick. Growth performed without GaAs and growth interruption resulted in decomposition of the p-InAs. When the scheme is used, the ensuing p-InAs first follows quasi-two-dimensional growth before favoring faceted islanding. Under 800-nm-wavelength femtosecond laser excitation, the p-InAs layer generates terahertz signals 70% of that of bulk p-InAs.
Source:IOPscience
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2017年7月27日星期四

A novel method of making high-quality vertical nanowires

A novel method of making high-quality vertical nanowires
Researchers in Japan have developed a novel way of growing high quality ferromagnetic nanowires in and on semi-conducting nanowire templates. Electron micrograph (a) shows a typical InAs nanowire template array, and (b) a heterojunction MnAs/InAs nanowire array. The ferromagnetic nanowires grow either inside (in the middle) or on top of the semiconducting nanowires, providing interesting electronic properties for future applications. Credit: Japan Society of Applied Physics (JSAP)

Researchers at Hokkaido University describe a novel method of making high quality vertical nanowires with full control over their size, density and distribution over a semi-conducting substrate. The findings are reported in the Japanese Journal of Applied Physics.

Nanowires hold interesting properties that are not found in bulk materials, making them useful in components for novel electronic and photonic devices. There is much interest in the development of vertical, free-standing nanowires, as their versatility shows great promise. However, most current designs use bottom-up fabrication techniques that result in vertical nanowires being randomly distributed on semi-conducting substrates, limiting their usability.

Now, Ryutaro Kodaira, Shinjiro Hara and co-workers at Hokkaido University have demonstrated a novel method of making high quality vertical nanowires with full control over their size, density and distribution over a semi-conducting substrate.

The team created an indium arsenide (InAs) nanowire template from which to grow the desired heterojunction nanowires, which were composed of ferromagnetic manganese arsenide (MnAs) and  InAs. In the fabrication process, they first produced the InAs nanowire template by precisely patterning circular openings in silicon dioxide thin films, which were deposited by plasma sputtering onto wafers. Next the researchers grew single InAs nanowires in each circular hole. The MnAs nanowires formed either inside (in the middle) or on top of the InAs nanowires, by a process known as 'endotaxy' – orientated crystal growth inside another crystal.

The MnAs nanowires had a hexagonal structure, exhibiting no defects or dislocations, and no contamination with other elements. The interface between the semi-conducting InAs nanowires and the ferromagnetic MnAs nanowires provides interesting possibilities for future devices. Indeed, Kodaira and Hara's team have already been using their new nanowires to carefully characterize magnetotransport properties of the nanowires for the potential fabrication of vertical spintronic device applications.

The nanowires could prove invaluable in next-generation sensing devices for electronic, photonic and bio-chemical applications. The new nanowires created by the team could widen the versatility of the  to even nano-scale spintronics.

More information: Ryutaro Kodaira et al. Synthesis and structural characterization of vertical ferromagnetic MnAs/semiconducting InAs heterojunction nanowires, Japanese Journal of Applied Physics (2016). DOI: 10.7567/JJAP.55.075503 

Provided by: Japan Society of Applied Physics



Source: Iopscience
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2017年7月19日星期三

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

Abstract

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.
Keywords:InAs wafer,
Source: Iopscience
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2017年7月7日星期五

Wafer-bonded coupled multilayer cavity with InAs quantum dots for two-color emission

Abstract

A GaAs/AlAs coupled multilayer cavity structure with InAs quantum dots (QDs) was fabricated by wafer-bonding of two cavity structures grown individually. The wafer-bonding technique is important to control the spatial distribution of nonlinear polarization for strong terahertz emission by the differential frequency generation of the two cavity modes of the coupled cavity. Three layers of self-assembled InAs QDs were inserted in a cavity grown on a (001) GaAs substrate as optical gain materials for two-color emission of the cavity mode lights. The other cavity with a GaAs cavity layer was grown on a (113)B GaAs substrate. Two-color emissions with a 3.8 THz frequency difference were successfully observed from the wafer-bonded coupled cavity by cw optical pumping at room temperature.
Keywords:InAs, InAs QDs,
Source:iopscience
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2017年6月28日星期三

Gate-induced transition between metal-type and thermally activated transport in self-catalyzed MBE-grown InAs nanowires

Electronic transport properties of InAs nanowires are studied systematically. The nanowires are grown by molecular beam epitaxy on a SiOx-covered GaAs wafer, without using foreign catalyst particles. Room-temperature measurements revealed relatively high resistivity and low carrier concentration values, which correlate with the low background doping obtained by our growth method. Transport parameters, such as resistivity, mobility, and carrier concentration, show a relatively large spread that is attributed to variations in surface conditions. For some nanowires the conductivity has a metal-type dependence on temperature, i.e. decreasing with decreasing temperature, while other nanowires show the opposite temperature behavior, i.e. temperature-activated characteristics. An applied gate voltage in a field-effect transistor configuration can switch between the two types of behavior. The effect is explained by the presence of barriers formed by potential fluctuations.

Keywords:InAs nanowires;

Source:iopscience


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