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To fabricate low-consumption and high-resolution gas sensors, especially for methane (CH4) gas (which has absorption around wavelength of 3.3 μm), mid-infrared LEDs are required. Accordingly, to reduce Shockley Read Hall recombination and achieve high luminous intensity at 3.3 μm, an AlxIn1-xSb LED with dislocation filter layers was developed. Dislocation density of the active layer was significantly reduced from 3.5 × 108 to 1.1 × 108/cm2, and luminous efficiency was doubled compared to that of conventionally structured LEDs. To our knowledge, emission intensity at 3.3 μm under injection current of 100 mA is the highest of any commercial LEDs.

High detectivity AlInSb mid-infrared photodiode sensor was fabricated on GaAs substrate. By inserting two pairs of 20 nm dislocation filter layers with high Al composition into n-type buffer layer, threading dislocation density was reduced to 1/3 or less. Resulting photodiode sensor showed high resistivity-area product (RA) of $19\ \mathrm{M}\Omega\mu \mathrm{m}^{2}$ and high normal-incidence detectivity of $1.7\times 10^{9}\ \mathrm{cm}\ \surd \mathrm{Hz}/\mathrm{W}$ at $3.3\ \mu \mathrm{m}$ at room temperature. To the best of our knowledge, this photodiode shows the highest performance in highly mismatched alloy system, i.e. AlInSb on GaAs substrate.

We have systematically investigated highly mismatched AlInSb photodiodes grown on GaAs substrates operating in the mid-infrared range. A novel characterization method was introduced to analyze the recombination mechanism within an active layer of the devices, which revealed a high conductance stemming from the leaky behavior of dislocations. The introduction of a dislocation filter layer successfully reduced threading dislocations and improved resistance area product of photodiodes, leading to high detectivity at room temperature.

We investigated difference in the transport properties between Al0.1In0.9Sb/InSb and Al0.1In0.9Sb/InAs0.1Sb0.9 quantum wells (QWs). The resistivity of InSb QWs increases exponentially with decreasing temperature, while that of InAs0.1Sb0.9 QWs is much lower than that of InSb QWs, showing low resistivity even at low temperature. Energy band diagram calculations of InAsxSb1−x/Al0.1In0.9Sb quantum wells (QWs) revealed that the bottom of the conduction band of the InAsxSb1−x well moves downward with increasing As content x. The bottom of the InSb QWs lies above the Fermi level (EF), resulting in depletion of the QW, while that in InAs0.1Sb0.9 QWs lies under EF at low temperature. These calculation results support the experimental difference of the resistivity and sheet carrier density between two types of the QWs well.

In this paper, we report the performance of room temperature operated mid-infrared light emitting diode (LED) with an InSb buffer layer and AlInSb active/barrier layers, which showed to be suitable for non-dispersive infrared (NDIR) gas sensing. Characterization of the LED was performed and we found that good carrier confinement and crystalline quality was responsible for its high performance. High efficiency light extraction was obtained by adopting backside emission architecture together with surface roughening treatment and TiO 2 anti-reflection coating. The fabricated AlInSb LED showed 75% higher power conversion efficiency when compared with a commercially available device. The developed LED, together with a commercially available infrared (IR) detector equipped with band-pass optical filter (AK9710, manufactured by Asahi Kasei Microdevices) were coupled into a mirror system forming a light path length of 80 mm, which was tested for CO 2 gas sensing. For a non-absorbing environment, sensor output of 8 nA was obtained by driving the LED with peak current of 100 mA and, by exposing the system at CO 2 concentration of 1000 ppm signal reduction due to absorbance around 12% was obtained.

We investigated the electrical and optical properties of a highly mismatched AlInSb/GaAs photodiode sensor working in the mid-infrared range at room temperature. A substantial increase in the device performance was achieved by controlling the strain energy density in the dislocation filter layers and barrier layers to reduce the density of threading and interfacial dislocations, respectively. The resulting photodiode showed a high resistance-area product of 0.24 Ω cm2 and a peak detectivity of 2.2 × 109 cm Hz1/2 W–1 at 3.3 μm.We investigated the electrical and optical properties of a highly mismatched AlInSb/GaAs photodiode sensor working in the mid-infrared range at room temperature. A substantial increase in the device performance was achieved by controlling the strain energy density in the dislocation filter layers and barrier layers to reduce the density of threading and interfacial dislocations, respectively. The resulting photodiode showed a high resistance-area product of 0.24 Ω cm2 and a peak detectivity of 2.2 × 109 cm Hz1/2 W–1 at 3.3 μm.

We studied the effect of Sb4 irradiation on the growth of GaAs thin films on Si (111) substrates. GaAs thin films were grown by molecular beam epitaxy (MBE) system with As2 as a source. Sb4 was also supplied during the GaAs growth. We evaluated surface roughness with an atomic force microscope and crystallinity with an X-ray diffraction system. When GaAs is grown without Sb4 irradiation, crystallinity can be improved by subjecting it to high temperatures, although the surface becomes very rough. In contrast, GaAs grown with Sb4 irradiation showed both good crystallinity and a very flat surface. As the growth temperature increased, both crystallinity and surface flatness were improved, probably due to the enhanced migration with two-dimensional growth modes. Furthermore, plan-view observation with a transmission electron microscope (TEM) showed that Sb4 irradiation was very effective for reducing stacking faults.

We investigated the spin–orbit interaction (SOI) in Al 0.1 In 0.9 Sb/Sn-doped InAs 0.1 Sb 0.9 quantum wells (QWs) with different doping levels using the weak anti-localization effect in the magneto-resistance. The inelastic scattering time is close to the T −1 law predicted theoretically for electron–electron interaction, and the spin–orbit scattering time is temperature independent as expected for the D'yakonov–Perel mechanism. The carrier-density dependence of zero-field spin-splitting energy extracted from the fits of magneto-resistance was examined by the theoretical calculation. The result confirms that the Dresselhaus SOI is much larger than the Rashba SOI in our QWs. The dominance of the Dresselhaus term in SOI originates in the large weight factor of InSb-based alloy.

We examined the role of localized electrons in the accumulation layer of Sn-doped InSb quantum wells (QWs) with various wellwidths ( L w = 15 ∼ 150 nm ) . At liquid He temperatures, the samples with the sheet resistance ρ > ρ c = h / e 2 for L w 30 nm exhibit the variable-range hopping (VRH), while those with ρ ρ c f o r L w > 50 nm exhibit weak localization (WL), where ρ c is the quantum resistance. In particular, a part of the electrons (with density of N str = 8 × 1 0 10 cm − 2 ) from Sn donors are trapped at the interface states at low temperatures below 77 K. In the WL regime, we observed the small positive magnetoresistance (MR) peak arising from the weak anti-localization (WAL) in the presence of spin-orbit interaction (SOI). In contrast to the WAL in WL regime, the low-field MR in the VRH regime remains entirely negative surviving the SOI, indicating that the hopping MR due to the quantum interference (QI) is completely negative regardless of the SOI. This result supports the predictions based on the directed-path approach for forward-scattering paths ignoring the back-scattering return loops for the QI in the VRH.

We have investigated the magneto-transport properties in InAs / AlGaSbAs quantum well (QW), where the lattice mismatch is less than 0.5%. In tilted magnetic fields, the spin-resolved subband-Landau-level coupling has been clearly observed in the magneto-resistance due to the large g -factor of this QW. An anomaly in the Hall effect has been observed at high magnetic fields of the filling factor being less than unity, which is caused by the coexistence of electrons and holes in the system.

InAs 0.1 Sb 0.9 active layers sandwiched between Al 0.1 In 0.9 Sb insulating layers were grown on GaAs(100) substrates by molecular beam epitaxy (MBE) where the InAs 0.1 Sb 0.9 active layers had no lattice mismatch with the Al 0,1 In 0.9 Sb layers. Basic transport properties and electronic properties of the InAs 0.1 Sb 0.9 were studied as functions of InAs 0.1 Sb 0.9 thickness. Very large electron mobility of InAs 0.1 Sb 0.9 active layers and very small thickness dependence at

Transport properties were investigated for undoped Al 0.1 In 0.9 Sb/ InAs 0.1 Sb 0.9 quantum wells (QWs), and two-carrier analyses were applied to the magnetic-field variations of the Hall coefficient and magnetoresistance at 77 K. The Hall coefficient increases with magnetic field, which shows coexistence of electrons and holes. This behaviour is similar to AlGaAsSb/ InAs QWs, which have a type-II band structure. Additionally, the Hall coefficient turns to decrease in more than 1 T, and the behaviour was not observed in the deep InAs QWs. This indicated that there are other electrons with different mobility. These are thought to be electrons extended over the QW, accumulated near the hetero-interface, and thermally excited in the barrier layer.

We studied the properties of InSb single-crystal thin films sandwiched by Al 0.1 In 0.9 Sb layers (with 0.5% lattice mismatch between InSb and Al 0.1 In 0.9 Sb) grown by molecular beam epitaxy on a GaAs substrate. The electron mobility of these InSb thin films was significantly higher and the electron density was very small in thin regions of less than 0.5 μm compared to InSb thin films directly grown on the GaAs substrate. These results mean that the Al 0.1 In 0.9 Sb layers almost eliminated the large lattice mismatch effect observed at the InSb/GaAs hetero-interface. The dependence of electron mobility and electron density on temperature is also discussed with respect to the InSb thickness and Sn doping.

It was found that the crystal quality, electron mobility and electron density of InAs single-crystal thin films grown directly on GaAs (1 0 0) substrates have a strong dependence on the film thickness. Moreover, tin doping increased the electron mobility compared to that of undoped InAs thin films. In addition, the tin doping reduced the temperature dependence of electron mobility and electron density of the InAs thin films. It is concluded from these results that tin doping during MBE growth of InAs can produce InAs single-crystal thin films suitable for magnetic sensors with a wide range of operation temperatures.

The heterointerfaces in InAs and InSb thin films grown on GaAs were found to affect the temperature dependence of the film's electrical properties such as electron mobility, electron density, and resistivity. The InAs and InSb surfaces of the films, which act as heterointerfaces with air, were found to similarly affect the electrical properties. It was found that the electron mobility of both InAs and InSb films grown on GaAs substrates has a three-layer structure.

We studied the effects of an AlGaAsSb electron supply layer for InGaAs/InAlAs metamorphic high electron mobility transistors (mHEMTs) on GaAs substrate. By implementing an AlGaAsSb electron supply layer, we drastically improved the electron mobility of InGaAs/InAlAs heterostructures for mHEMTs. An AlGaAsSb electron supply layer for InGaAs/InAlAs heterostructures on GaAs substrates promises high-performance mHEMTs with low production cost.

Weak-field magnetoresistance (MR) in the variable-range hopping (VRH) in the presence of spin–orbit interaction (SOI) for 2DEGs at the hetero-interface of InSb quantum wells was examined in view of the quantum interference (QI) effect. Samples with the sheet resistance, ρ > ρ c = h / e 2 , exhibit VRH, while those with ρ ρ c exhibit weak localiz a tion (WL) at low temperatures, where h / e 2 is the quantum resistance. In the WL regime, a positive magnetoresistance (MR) peak due to the weak anti-localization (WAL) with SOI is clearly observed in low magnetic field. In contrast, the low-field hopping MR remains entirely negative surviving the SOI, indicating that the hopping MR due to the QI is completely negative regardless of the SOI. This result supports the predictions based on the directed-path approach for forward-scattering paths ignoring the back-scattering return loops for the QI in the VRH.

InAs0.1Sb0.9 active layers sandwiched between Al0.1In0.9Sb insulating buffer layers were grown on GaAs (100) substrates by molecular beam epitaxy. The basic transport properties at room temperature and quantum Hall effects at low temperature of the InAs0.1Sb0.9 were studied as a function of InAs0.1Sb0.9 thickness. The electron mobility of the InAs0.1Sb0.9 active layers had a very high value and very small thickness dependence at less than 500nm. The quantum Hall effects of the InAs0.1Sb0.9 were observed at thicknesses 15, 20, 30, 50, 70, and 100nm. The observation of the quantum Hall effect at thickness more than 50nm strongly suggests the existence of two-dimensional electron gas in the InAs0.1Sb0.9 layer sandwiched between Al0.1In0.9Sb layers.

La-NMR, Hall coefficient and sound velocity have been measured in order to investigate the correlation between the magnetic ordering, the prominent change of transport properties, the suppression of T c and the structural transformation around x∼1/8 in La 1.96−x Y 0.04 Sr x CuO 4. By the substitution of 0.04/2 Y for La-sites, the structural transformation to the low temperature tetragonal phase (LTT) is caused at 57±14 K for samples around x∼0.115. The. prominent decrease of the Hall coefficient followed by the sign reversal and the magnetic ordering are observed around x∼0.115 below temperatures T s and T N, respectively. T s vs x shows a bell shaped curve with the maximum value of 65 K at x∼00115 where most prominent suppression of T c appears. T N shows similar x dependence to T s with the maximum value of 40 K at x∼0.115. The change of the electronic state below T s and the suppression of T c become more prominent and the magnetic ordering is observed more wide range of x under the LTT phase.

The formation and evolution of rotational twin (TW) domains introduced by a stacking fault during molecular-beam epitaxial growth of GaAs on Si (111) substrates were studied by in situ x-ray diffraction. To modify the volume ratio of TW to total GaAs domains, GaAs was deposited under high and low group V/group III (V/III) flux ratios. For low V/III, there was less nucleation of TW than normal growth (NG) domains, although the NG and TW growth rates were similar. For high V/III, the NG and TW growth rates varied until a few GaAs monolayers were deposited; the mean TW domain size was smaller for all film thicknesses.

We have investigated transport properties in InAs/AlGaSbAs and InAsSb/AlInSb quantum wells (QW) in the quantum Hall regime. The carrier density in InAs QW is tuned by using a front gate bias, and the contour plot of resistance as a function of perpendicular magnetic field and gate voltage reveals the spin‐resolved subband‐Landau‐level coupling in tilted magnetic fields. An anomalous transport occurred by the coexistence of electrons and holes in the system has been observed both in InAs and InAsSb QWs.

Electron mobilities of InSb, InSb/AlInSb and InAsSb/AlInSb grown on GaAs(100) were compared as a function of layer thickness and temperature. InAs0.1Sb0.9 thin active layers sandwiched by Al0.1In0.9Sb layers showed the smallest thickness dependence and very large electron mobility at less than 500nm thickness. Basic transport properties and Sn doping effects of the InAs0.1Sb0.9 were studied.

The resistivity of InAs0.1Sb0.9/Al0.1In0.9Sb quantum wells (QWs) is much lower than that of InSb/Al0.1In0.9Sb QWs, staying low resistivity even at low temperature. Fundamental difference in low temperature transport properties between InSb/Al0.1In0.9Sb and InAs0.1Sb0.9/Al0.1In0.9Sb QWs was revealed, based on the band diagram calculations of these QWs. Band diagrams of InAsxSb1−x/Al0.1In0.9Sb QWs showed that the energy band of the InAsxSb1−x layer moves downward with increasing As content x. The QW is type I at x equal to 0, becomes type II at x equal to 0.1. The Fermi level (EF) of the InSb QWs lies in the band gap and below apart from the bottom of the conduction band, while EF of the InAs0.1Sb0.9 QWs is above the bottom of the conduction band of the well. The calculated sheet carrier densities are in good agreement with the experimental results. It well explains that the sheet carrier density difference between InSb and InAs0.1Sb0.9 QWs mainly originates from this band diagram difference and the position of EF.

The effect of doping on InSb/Al0.1In0.9Sb quantum wells (QWs) was investigated, and it was found that doping improves the electron mobility at low temperatures and leads to a weaker dependence of the resistivity with temperature. The dependence of the carrier density on the well width revealed trap states at the interfaces of the QW whose sheet density per interface was estimated to be about 4 × 1010 cm−2. The low mobility of undoped InSb QWs, in particular, at low temperature seems to have been caused by positively ionized impurity scattering at the interfacial trap states. Doping compensates for the trap states and enhances mobility by suppressing ionized impurity scattering. Thus, intentional doping is necessary for developing high-mobility InSb QW devices. The origin of the trap states is qualitatively discussed.

We investigated the transport properties of the Al 0.1 In 0.9 Sb/InAs 0.1 Sb 0.9 quantum wells (QWs). Intentional doping of donors to the QW is effective to decrease the sheet resistance and suppress its temperature dependence because the carrier density is maintained to be relatively high in low temperature. Additionally, although there exists a low mobility region near the heterointerface of the QW and a high mobility region far from the interface in this system, the doped electrons contribute to keep high mobility in low temperature because the increase of electrons prevents the accumulation of all electrons in the low mobility region.