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Abstract: Heterostructures consisting of an InGaSb quantum well situated between AlGaSb barriers were grown by molecular beam epitaxy. Calculations indicate a type-I band structure with substantial valence and conduction band offsets that can allow for the confinement of either electrons or holes in the InGaSb. Quantum wells with n-type conduction were achieved using modulation doping, with Te located in the barrier above the quantum well. A set of barrier layers was found which resulted in a sample with an In0.2Ga0.8Sb quantum well that exhibited an electron mobility of 3900cm2/Vs as grown. After removal of upper barrier layers including the Te by selective etching, the conductivity switched to p-type, with hole mobilities near 800cm2/Vs. This design could allow the integration of low-power n- and p-channel field-effect transistors for complementary logic applications. [Copyright &y& Elsevier]

Abstract: C60 uniformly doped and δ-doped GaAs layers are grown by migration enhanced epitaxy method. Crystalline and electrical characteristics of the layers are investigated by reflection high energy electron diffraction, X-ray diffraction and capacitance–voltage (C–V) measurements. C60 high-concentration doping is found to introduce 2D defects, and X-ray diffraction pole-figure measurements show that the rotational domains appear predominantly on {111}A plane. This indicates that C60 molecules are mainly incorporated on the dangling bonds of Ga atoms due to the high binding energy between C60 molecules and Ga atoms. C60 uniformly doped GaAs layers show highly resistive characteristics, suggesting that C60 molecules cannot be decomposed into isolated C atoms in the GaAs lattice, and they behave as if they were electron traps or strong recombination centers. C–V profiles of Cr–Au/C60 δ-doped GaAs Schottky diode suggest that C60 molecules in GaAs lattice produce electron traps which can be charged or discharged by applied electrical field. [Copyright &y& Elsevier]

Abstract: MBE-grown single-crystal Gd2O3 epitaxially on GaN has exhibited excellent thermal stability, withstanding rapid thermal annealing (RTA) at 1100°C. The high-κ dielectric Gd2O3 thin film 10nm thick has a monoclinic phase with a high degree of crystallinity, characterized by X-ray diffraction using synchrotron radiation. The orientation relationship is and . Interface between Gd2O3 and GaN remains atomically sharp after the RTA, as demonstrated using X-ray reflectivity and high-resolution transmission electron microscopy. Gd2O3/GaN metal-oxide-semiconductor capacitors show well-behaved capacitance–voltage characteristics with small dispersion and hysterisis, a high dielectric constant of ∼17, and a low electrical leakage current density of 4.6×10−9 A/cm2 at 1MV/cm. [Copyright &y& Elsevier]

Abstract: Depletion-mode In0.2Ga0.8As/GaAs metal-oxide-semiconductor field-effect transistors (MOSFETs) were fabricated with molecular beam epitaxy (MBE) grown Al2O3/Ga2O3(Gd2O3) as the gate dielectric in two comparable processes. In the “metal-gate-last” process, a 12μm gate-length depletion-mode n-channel InGaAs/GaAs MOSFET with a Ga2O3(Gd2O3) gate oxide 6nm thick shows an accumulated drain current density of 135mA/mm at V g=2V. In the other process of “metal-gate-first” process, the device with same gate dielectric, channel, and gate length exhibits a larger drain current density of 175mA/mm at the same gate bias. In addition, there is a broader transfer characteristics and higher extrinsic peak transconductance of 48mS/mm in the metal-gate-first process. MOS capacitors from both processes have exhibited excellent capacitance–voltage (C–V) characteristics with minor dispersion, negligible hysteresis, and κ values of 13.7–13.9 in Ga2O3(Gd2O3). [Copyright &y& Elsevier]

Abstract: Transport properties were investigated for undoped Al0.1In0.9Sb/ InAs0.1Sb0.9 quantum wells (QWs), and two-carrier analyses were applied to the magnetic-field variations of the Hall coefficient and magnetoresistance at 77K. 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 1T, 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. [Copyright &y& Elsevier]

Abstract: InAs0.1Sb0.9 active layers sandwiched between Al0.1In0.9Sb insulating layers were grown on GaAs(100) substrates by molecular beam epitaxy (MBE) where the InAs0.1Sb0.9 active layers had no lattice mismatch with the Al0.1In0.9Sb layers. Basic transport properties and electronic properties of the InAs0.1Sb0.9 were studied as functions of InAs0.1Sb0.9 thickness. Very large electron mobility of InAs0.1Sb0.9 active layers and very small thickness dependence at <500nm were observed. The large lattice mismatch effect observed for InSb active layers grown directly on GaAs substrates and for an InSb active layer sandwiched between Al0.1In0.9Sb was almost completely eliminated. [Copyright &y& Elsevier]

Abstract: Quantum wells of GaSb were grown by molecular beam epitaxy on GaAs substrates. The buffer layer and barrier layers consisted of relaxed AlAs x Sb1− x . The composition of the AlAs x Sb1− x was varied to produce compressive biaxial strains in the GaSb. The confinement and strain in the GaSb quantum wells lift the degeneracy in the valence band, resulting in lower in-plane effective mass and higher mobility. A three-fold enhancement of mobility was achieved, with room-temperature mobilities as high as 1350cm2/Vs and 77K values as high as 10,400cm2/Vs for strains near 1%. These quantum wells should be suitable for high-performance p-channel field-effect transistors for complementary circuits operating at extremely low power. [Copyright &y& Elsevier]

Abstract: The elaboration of Gallium nitride (GaN)-based high electron mobility transistors (HEMTs) structures is comparatively investigated on cubic SiC/Si(111) templates and on silicon substrates. As compared with silicon, 3C-SiC/Si(111) template is less sensitive to the detrimental nitridation effect of ammonia, and it allows a reduction of the stress in GaN films due to both lower lattice and thermal expansion coefficient mismatch. Crack-free GaN layers and AlGaN/GaN HEMTs with total thicknesses exceeding 2μm were successfully grown by molecular beam epitaxy on optimized 0.8-μm-thick 3C-SiC/Si templates elaborated by chemical vapor deposition. A threading dislocation density below 5×109 cm−2 and a two-dimensional electron gas with a sheet carrier concentration of 1.1×1013 cm−2 and an electron mobility of 2050cm2/Vs at room temperature have been obtained. The feasibility of the 3C-SiC/Si(111) approach is demonstrated by the structural and electrical quality of these structures, as well as the characteristics of transistors that are at least equivalent to reference transistors realized on bulk silicon substrates. [Copyright &y& Elsevier]

Abstract: The electrical characteristics of magnesium (Mg)-doped GaAs epitaxial layers grown with different substrate temperatures have been investigated by Hall effect and capacitance–voltage (C–V) measurements at room temperature. The carrier concentration obtained by Hall measurements was decreased from 1.4×1019 to 3.4×1016 cm−3 when increasing the substrate temperature in the range 460–540°C, and thus the maximum attainable doping density was N A–N D=1.4×1019 cm−3. The depth profiles of doping density, obtained by C–V measurements, show that carriers largely out-diffused toward the surface. This could be attributed to the surface segregation effect, which was predominant in the samples with a high doping density than those with a low doping density. Mg-doped GaAs layers have higher mobility than Be-doped GaAs layers around N A–N D=1018 cm−3. Thus, it is expected that Mg could be effectively used as p-type dopants for highly doped nanostructured semiconductors. [Copyright &y& Elsevier]

Abstract: The regrowth of AlGaN/GaN high electron mobility transistor (HEMT) structures on semi-insulating (SI) GaN templates, after exposure to air, results in the presence of parasitic conducting channels at regrowth interface (RI). Air contamination of the SI GaN templates is responsible for n-type doping and explains this parallel conduction. The parasitic conducting channel results in poor pinch-off characteristics (I leakage∼1mA/mm at bias gate–source voltage above pinch-off voltage) and poor inter-device isolation and makes necessary to equip reactors with acceptor sources to compensate the n-type doping at the RI. To overcome this, we developed a new method of local Fe doping used in GaN templates for inhibiting RI pollution and proved to be efficient. Using this annihilation method permits to reduce by several orders of magnitude buffer leakage current. Such HEMT structures regrown by metalorganic vapor phase epitaxy (MOVPE) or by molecular beam epitaxy (MBE) exhibit two-dimensional electron gas (2DEG) with 300K mobilities above 2000cm2/Vs at carrier densities 9–10×1012 cm−2 with a perfect charge control. [Copyright &y& Elsevier]

Abstract: In this work, we show that, by carefully designing the subsurface Fe doping profile in SI-GaN templates grown by MOVPE and by optimizing the MBE regrowth conditions, a highly resistive GaN buffer can be achieved on these epi-ready GaN-on-sapphire templates without any addition of acceptors during the regrowth. As a result, high-quality high electron mobility transistors can be fabricated. Furthermore, we report on the excellent properties of two-dimensional electron gas and device performances with electron mobility greater than 2000cm2/Vs at room temperature and off-state buffer leakage currents as low as 5μA/mm at 100V. [Copyright &y& Elsevier]

Abstract: We compared the magnetization curves between as-grown and free standing GaMnAs samples, which were obtained from the same epitaxially grown wafer, to study the influence of epitaxial strain on their ferromagnetic properties. We found that the magnetization and coercive field for the free standing sample have significantly increased about twice as large as those of the as-grown GaMnAs. In addition, the uniaxial ferromagnetic anisotropies, which would not be expected on the basis of crystal symmetry, are remarkably different between the two samples. These results undoubtedly demonstrate that the magnetic properties are strongly influenced by the epitaxially induced strain. [Copyright &y& Elsevier]

Abstract: The growth of dilute nitride alloys of GaInSb by plasma-assisted molecular beam epitaxy is reported. The principle of lattice matching GaInNSb alloys to GaSb(001) substrates is demonstrated. High resolution X-ray diffraction rocking curves and reciprocal space maps indicate the high crystalline quality of the GaInNSb layers and illustrate a lattice match to GaSb with nitrogen and indium incorporations of 1.8% and 8.4%, respectively. The rms roughness of a nominally lattice matched GaInNSb/GaSb(001) layer was determined from atomic force microscopy to be . [Copyright &y& Elsevier]

Abstract: We investigated the contact resistance of a non-alloyed Ti/Pt/Au ohmic electrode to obtain thermally stable source–drain resistance of cryogenically cooled high electron mobility transistors (HEMTs) fabricated on (411)A-oriented InP substrates by molecular beam epitaxy. A contact resistance of , which strongly depended on InAlAs spacer and barrier layers, was achieved at 16K (25% below the value at 300K) for the non-alloyed Ti/Pt/Au ohmic electrode formed on the HEMT structure with 3-nm-thick InAlAs spacer and 10-nm-thick InAlAs barrier layers. For a 195-nm-gate HEMT, we achieved a maximum transconductance of at 16K (26% above the value at 300K), which, to our knowledge, is one of the highest values for HEMTs ever reported. This extremely high was attributed to not only 33% lower source–drain resistance ( at 16K) because of thermally stable and low contact resistance but also 19% lower transit time under the gate (0.39ps at 16K) because of phonon scattering suppression compared with the 300K values. [Copyright &y& Elsevier]

Abstract: In nanostructures, the surface-to-volume ratio is increased, and surface state problems become more serious, making success of the future III–V nanoelectronics strongly dependent on surface passivation. To solve this problem, we have been investigating a passivation scheme using a Si interlayer called Si interface control layer (Si ICL) [H. Hasegawa, Thin Solid Films 367 (2000) 58]. However, main efforts have been limited on (001) surfaces. This paper investigates the applicability of the Si ICL approach to (111)B surfaces. An ultrathin (1nm) silicon layer was grown by MBE on GaAs and AlGaAs (111)B surfaces with (2×2), and (1×1) surface reconstructions. Surfaces were characterized by in situ X-ray photoelectron spectroscopy (XPS) technique. Si layers grew epitaxially with Si–Ga bonds at the Si/GaAs interface and Si–As termination on top, suggesting surfactant roles played by As atoms. On nitridation of Si layer by nitrogen radicals at room temperature, Si–As bonds were replaced by Si–N bonds leading to partial nitridation of the Si layer. Unlike the case of the As-stabilized GaAs (001)-(2×4) surface, large reduction of band bending by 250–420meV took place on (111)B surfaces, indicating large reduction of surface states. The results indicate effectiveness of the Si ICL passivation on (111)B surface. [Copyright &y& Elsevier]

Abstract: Electronic g-factors are investigated in selectively doped n-AlGaAs/GaAs heterojunctions with embedded InGaAs quantum dots (QDs). By measuring the magneto-resistivity and analyzing the separation of spin split peaks of the Shubnikov–de Haas (SdH) oscillations, the magnitudes of g-factors are estimated. It is found that the g-factor for a sample with InGaAs QDs is lower than that for the reference sample without QDs. We also compare the SdH oscillations with a semi-empirical model and estimate the exchange interaction of 2D electrons, which mainly dominates the g-factor in a strong magnetic field. It is found that exchange energy for the sample with QDs is lower than that of the reference sample, suggesting that the presence of QDs weakens the exchange interaction of nearby 2D electrons. [Copyright &y& Elsevier]

Abstract: The influence of the nitrogen doping in GaMnAs on the magnetic properties was investigated. The GaMnNAs film was grown by molecular beam epitaxy with a nitrogen plasma source. The GaMnNAs film with a large amount of nitrogen showed super-paramagnetic behaviour. The Arrott-plot and the Curie–Weiss plot also support the paramagnetism. The high concentration of nitrogen caused suppression of the ferromagnetism. One of the possibilities of the suppression is due to the band gap bowing effect, which causes the anti-bonding state of 3d-Mn to locate in the valence band in high nitrogen concentration. [Copyright &y& Elsevier]

Abstract: AlGaN/GaN high electron mobility transistor (HEMT) structures were grown on 4H-SiC (0001) vicinal substrates with vicinal angles of 0.4°, 1° and 2° inclined toward , as well as 0° (just substrate) by radio-frequency plasma-assisted molecular beam epitaxy (rf-MBE). It was found that the mobility was enhanced by increasing the vicinal angle, particularly, the mobility in the sample grown on a 2°-off substrate exhibited 8600cm2/Vs in contrast to that grown on a just sample (3310cm2/Vs) at 30K. In addition, the anisotropic two-dimensional electron gas (2DEG) mobility of the vicinal samples was clearly found, where the mobility at 30K along the direction (parallel to the macro step) and that along direction (perpendicular to the macro step) were 5490 and 1600cm2/Vs, respectively, for the 1°-off sample. The enhancement of the 2DEG mobility is considered to be due to the improvement of film qualities by using vicinal substrates. [Copyright &y& Elsevier]

Abstract: InAs layers grown by molecular beam epitaxy at 150-350°C were characterized by electron probe microanalysis (EPMA), high resolution X-ray diffraction (HRXRD), Hall measurements, and secondary ion mass spectrometry (SIMS). EPMA revealed that the As mole fractions in the layers grown at 150–200°C are higher by about 0.5% than those in the layers grown at 300–350°C. HRXRD measurements revealed that the layers grown at 150–200°C have larger lattice spacings than the InAs substrate by about 0.02%. Hall measurements revealed that the free-electron concentration in the layer grown at 200°C is as high as 1.4×1019 cm−3 while such a high concentration of impurities cannot be detected by SIMS. Upon annealing at higher temperatures than 250°C, both the lattice spacing and the free-electron concentration of the layer grown at 200°C were observed to decrease. These phenomena can be reasonably attributed to antisite As. [Copyright &y& Elsevier]

Abstract: We studied the properties of InSb single-crystal thin films sandwiched by Al0.1In0.9Sb layers (with 0.5% lattice mismatch between InSb and Al0.1In0.9Sb) 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 0.5μm compared to InSb thin films directly grown on the GaAs substrate. These results mean that the Al0.1In0.9Sb 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. [Copyright &y& Elsevier]

Abstract: In this work we show how in situ measurements of wafer curvature helps for monitoring the strain relaxation in group-III-nitride layers grown by molecular beam eptixay on silicon. In particular, we show the efficiency of GaN/AlN interlayers for growing high quality AlGaN/GaN heterostructures with residual stress that largely compensates the one appearing upon cooling down to room temperature. [Copyright &y& Elsevier]

Abstract: We report the growth and characterization results of AlGaN/GaN heterostructures using quasi AlGaN as a barrier layer, which is formed by AlN/GaN super-lattice. It is found that the surface morphology of the heterostructure is greatly improved, where monolayer steps on the surface are clearly observed. Simultaneously, electric properties in such structures are superior to those using the conventional alloy AlGaN caplayers. Low sheet resistance (less than 200Ω/□) is obtained from our samples with high Al composition (>40%) in average, which shows the great merit of our growth method to the conventional technique. It is expected that the technique can be applied to the high power and high frequency device applications. [Copyright &y& Elsevier]

Abstract: Surface diffusion is one of the most common phenomena during the thin-film growth. The microstructure of the thin film depends on the rate of surface diffusion of the adatoms. In this paper, we theoretically show the effect of external field on surface diffusion barrier using gallium nitride as an example. We show, via density functional calculation, that the desorption energy of surface adsorbed atom and activation barrier for surface diffusion process can be altered by application of external field. Finally, based on the arguments of the electronic effect, we analyze the origin of the effect of the external field and its orientation on desorption energy and activation barrier for surface diffusion. [Copyright &y& Elsevier]

Abstract: We present experimental results on a technique for alloy composition grading within distributed Bragg reflectors (DBRs) for use in vertical-cavity, surface-emitting lasers (VCSELs). This technique, implemented using molecular beam epitaxy (MBE), employs multiple group-III sources, with different fluxes, to realize a set of Al x Ga1− x As compositions without changing cell temperatures. By varying the source combination and layer thickness, different functional forms of compositional grading, such as linear and parabolic, can be closely approximated. This method, in combination with modulated doping profiles, was used to grow 980nm VCSELs with low threshold currents, high output powers, and threshold voltages less than 1.45V. [Copyright &y& Elsevier]

Abstract: Different growth modes have been identified in thick (⩾500nm) AlGaN and InGaN layers grown by plasma-assisted molecular beam epitaxy as a function of parameters such as the growth temperature or the III–V ratio. Al mole fractions between 0% and 60% have been explored in AlGaN alloys, finding that a two-dimensional growth only occurs above a critical temperature under a metal-stable regime. This critical temperature increases with the Al content and depends strongly on the strain induced by the substrate and previous layers. A thermodynamical model is proposed to explain this behaviour. InGaN layers were also grown with In compositions in the 0–10% range. In this case, a metal-stable regime may induce In accumulation at the surface preventing the InGaN growth. Thus, slightly N-rich conditions are needed to reach an efficient In incorporation. To broaden the photodetection range of III-nitrides, photoconductors have been fabricated on both ternary alloys aiming to obtain high responsivity, solar-blind UV detectors (AlGaN) and narrow-band visible detectors (InGaN). [Copyright &y& Elsevier]

Abstract: We study the transport properties of molecular beam epitaxial films with and , 0.5 and 7%. We find that the hole concentration decreases with increasing Cr content, which can be attributed to increasing hole localisation in the impurity band. Our data indicate that carrier hopping or tunnelling are the main conduction mechanisms in the samples. We find no evidence of ferromagnetic ordering in the films co-doped with Mn and Cr. [Copyright &y& Elsevier]

Abstract: It was found that the crystal quality, electron mobility and electron density of InAs single-crystal thin films grown directly on GaAs (100) 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. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: InP high electron mobility transistor (HEMT) structures with In0.53Ga0.47As channels and In0.52Al0.48As barriers were grown by molecular beam epitaxy. A GaTe source was used as an n-type dopant. Conventional structures with 50–100Å InAlAs(Te) layers and Te-delta-doped structures were investigated. Both types of structures exhibited good transport characteristics, with mobilities of 8000–10,000cm2/V-s and sheet densities of 1–4×1012/cm2. Fluorination studies showed similar behavior for Si- and Te-doped HEMT structures, with donor deactivation resulting in substantial reductions in mobility and carrier density after exposure to fluorine. [Copyright &y& Elsevier]

Abstract: We have investigated the scattering mechanisms limiting the low-temperature electron mobility in unintentionally doped In0.75Al0.25As/In0.75Ga0.25As metamorphic quantum wells grown on GaAs (001) substrates. We found that the mobility is limited by background impurity scattering for densities lower than 2.0×1011 cm−2, and by the combination of this mechanism and alloy disorder scattering for higher densities. From such analysis we estimate an alloy disorder scattering potential of about 0.5±0.1eV. Moreover we show that when a strained InAs layer is located in the centre of the In0.75Ga0.25As well, the alloy disorder scattering can be reduced, yielding mobilities up to 320000cm2/Vs at a carrier concentration of 3.1×1011 cm−2. [Copyright &y& Elsevier]

Abstract: We have investigated nitrogen- (N-) induced scatterings in GaAsN, AlGaAsN and InGaAsN systems by conventional parameter fitting analysis for temperature dependence of Hall electron mobility. It has been revealed that the temperature dependence of the Hall electron mobility of GaAsN and AlGaAsN are completely different in low-temperature range below 200K, and an influence by an unknown scattering mechanism induced by N incorporation in GaAsN is considerably larger than that in AlGaAsN, in spite of the fact that lattice mismatches of the two systems are almost equal. The results strongly indicate that an inhomogeneous N spatial distribution in GaAsN is closely related with increase of the unknown scattering contribution induced by N incorporation. Temperature dependence of the Hall electron mobility and N-induced scattering contribution in InGaAsN show a tendency similar to those in the AlGaAsN, because of the preferential bond formation of In–N bonds during InGaAsN growth. The results strongly suggest that N atoms should be bonded with In atoms preferentially such as clusters and such clusters distributed randomly in order to compensate the strong local strain induced by N incorporation for the high-quality InGaAsN growth. [Copyright &y& Elsevier]

Abstract: In this paper, we report on the properties of AlGaN/GaN/AlGaN HEMT structures grown by molecular beam epitaxy on resistive Si(111) substrates. The properties of the AlGaN buffer layer and the AlGaN/GaN HEMTs are presented. Finally, the static performances of long gate length devices demonstrate their interest for power applications. [Copyright &y& Elsevier]

Abstract: In this work, AlGaN/GaN high electron mobility transistors have been grown by ammonia source molecular beam epitaxy (MBE) on silicon (111), silicon carbide and GaN templates on sapphire. The structural and electrical properties of these layers have been studied in order to determine the impact of substrate choice and buffer layer on active layer quality. Furthermore, an intercalated AlN layer grown on a GaN template is shown to enhance the insulating properties of the buffer. [Copyright &y& Elsevier]

Abstract: Using plasma-assisted molecular beam epitaxy (MBE), GaN x Sb1− x films have been grown onto GaSb and GaAs substrates over a range of growth temperatures (310–460°C). The films showed excellent crystalline quality and a nitrogen incorporation of 0–1.75% measured by X-ray diffraction. These materials should enable access to wavelengths in the 2–4μm range. [Copyright &y& Elsevier]

Abstract: We have grown InGaAs/AlAsSb single quantum wells (SQWs) with AlAs diffusion-stopping layers of various thicknesses by molecular beam epitaxy. X-ray diffraction rocking curve measurements as well as optical microscope observations indicated good structural quality of the samples having less than 4-monolayer (ML) AlAs layers, which were inserted between InGaAs wells and AlAsSb barriers. Near-infrared absorption measurements revealed that when only 2-ML AlAs layers were inserted at the interfaces, the absorption coefficient of intersubband transition in the conduction band was significantly enhanced, and the peak wavelength was greatly shifted toward shorter wavelengths. This improvement in the optical quality confirms that thin AlAs layers efficiently reduce atomic interdiffusion at the interfaces. The results of the absorption measurements also suggest that such interdiffusion occurs more readily at the lower interface of the InGaAs well than at the upper interface. [Copyright &y& Elsevier]

Abstract: Pseudomorphic trench-type InGaAs/InAlAs quantum-wire field-effect transistors (QWR-FETs) are realized on (311)A InP V-groove substrates by selective molecular beam epitaxy. Negative differential resistance (NDR) spectra are clearly observed in the 50–240K temperature range for the In0.7Ga0.3As QWR-FET, and up to 260K for the In0.8Ga0.2As QWR-FET. These temperature ranges are higher than that of a lattice-matched QWR-FET, and this is thought to be due to the higher electron mobility in the pseudomorphic QWR layer. The NDR temperature range increases as the QWR In content increases and the FET gate length decreases. [Copyright &y& Elsevier]

Abstract: The Mg-doping efficiency in GaN layers grown by molecular-beam epitaxy has been studied as a function of the growth temperature, the growth rate, and the Mg beam flux. The Mg cell temperature window for efficient p-type doping is rather narrow, being limited by the GaN n-type background doping density (lower limit) and by the Mg surface coverage that, beyond a threshold, induces a layer polarity inversion (N-polarity), leading to a reduction of the Mg incorporation (upper limit). An increase of the growth temperature avoids this polarity inversion, but the Mg flux must be increased to compensate the strong desorption rate. Thus, a trade-off between both temperatures has to be reached. A reduction of the growth rate has a strong effect on the p-type doping level, yielding up to 7×1017holes/cm3 for a total Mg concentration of 1×1019cm-3. This high Mg concentration does not seem to generate Mg-related defects or deep traps. [Copyright &y& Elsevier]

Variable magnetic field Hall effect measurements were performed on InN samples grown by molecular beam epitaxy. Since mixed conduction effects due to both the presence of multiple conducting layers and sample inhomogeneity were present, standard measurements yielded only averaged results. The variable field approach allowed direct measurement of interfacial/surface conduction while also allowing determination of the bulk electrical properties. Analysis always indicated electrons with more than one value of mobility, often with a significant spread in the mobility. This suggests multiple conduction layers in the sample as well as sample inhomogeneity. Variable magnetic field analysis of a 7.5 μm thick InN sample suggests maximum mobilities greater than 4000 cm2/Vs in “bulk” InN. The quantitative mobility spectrum analysis technique, reported here for the first time on InN, indicated a continuous and significant spread in mobility for the bulk electron, likely with sample thickness. [Copyright &y& Elsevier]

InSb heteroepitaxial thin films were grown on GaAs (0 0 1) substrate by the temperature variation two-step growth process. X-ray rocking curve widths and electrical properties of the InSb films with different thickness were investigated. The best value of a 2-μm thick InSb film had an X-ray rocking curve width of 277 arcsec and room-temperature Hall mobilities, the carrier concentrations obtained were 55,000 cm2/V s and 1.5×1016/cm3, respectively. The enhanced mobilities and reduced carrier concentration of InSb films suggested a low defect density due to confinement of the dislocation in the InSb/GaAs interface. [Copyright &y& Elsevier]

Photoluminescence (PL) of quantum dots embedded in high potential barriers is studied as functions of barrier thickness and temperature. With the increase of barrier thickness, both the strengthened two-dimensional electron gas (2DEG) structure and strongly localized electron wave functions can increase the carrier recombination. The optical properties of two different-barrier-thickness samples exhibit different characteristics with the decreased measurement temperatures. The PL recombination characteristic of the samples with the barriers adjacent to a Si-doping GaAs layer is different from that of samples with the barrier adjacent to an i-GaAs layer. [Copyright &y& Elsevier]

InAs quantum wells clad by AlSb barriers contain an unintentional electron density of approximately 1×1012 cm−2. This report concerns the compensation of these electrons by p-type modulation doping with Be. The electron concentration in the InAs quantum well decreases linearly with increasing Be doping as expected from lever rule arguments. Hall measurements show that the electron mobility increases with increasing electron concentration at temperatures between 10 and 300 K. These findings need to be considered in the design of field-effect transistors based on this material system. [Copyright &y& Elsevier]

The influence of InAs growth rate and the group V–III beam equivalent pressure ratio on the optical and structural properties of InAs quantum dots in constant and graded composition (In,Ga)As quantum wells is investigated. Optimized growth conditions are found for both structures. It is suggested that the “dots-in-a-graded-well” structure might serve as a better active medium than the “dots-in-a-well” structure. Both structures are engineered to emit at the important telecommunication wavelength of 1.3 μm. [Copyright &y& Elsevier]

The temperature dependence of the transport properties of undoped and Sn-doped InSb single crystal thin films grown on GaAs substrates by MBE were investigated. The temperature dependence of undoped InSb thin films was large and had maximum near room temperature, whereas the Sn-doped thin films showed very small and monotonic decrease with increasing temperature. The electron mobility of the films varied significantly in the growth direction from the InSb/GaAs hetero-interface to the InSb thin film surface. This large variation of the electron mobility in the growth direction explained the observed temperature dependence of the electron mobility for these films. The large variation of the electron mobility in the growth direction was described by a simple model of two layers with a low electron mobility layer near the hetero-interface and the other with a high electron mobility. These InSb films were used to fabricate practical and highly sensitive Hall sensors with a very small temperature dependence. [Copyright &y& Elsevier]

Structural defects in InSb/AlxIn1−xSb quantum-well samples grown on (0 0 1) GaAs substrates have been investigated using transmission electron microscopy. A high density of dislocations is created at the interface between the InSb nucleation layer and the substrate, while {1 1 1}-planar defects are introduced at various locations. An InSb/AlxIn1−xSb interface 920 nm above the InSb/GaAs interface acts as a trapping site for many dislocations. The majority of the {1 1 1}-planar defects are micro-twins with {1 1 1}-bilayer thickness fluctuations. The anisotropic distribution of the micro-twins correlates with the measured anisotropic electron mobility in the quantum well. [Copyright &y& Elsevier]

The GaAsSb/GaAs conduction band alignment is determined to be almost flat (weak type-I) in the 0.3 Sb mole fraction neighborhood where 1300 nm emission is observed. Based on photoluminescence measurements and modeling the bandgap bowing parameter of pseudomorphic GaAsSb on GaAs is determined to be −2.0 eV with the bowing distributed 45% to the conduction band. Using these parameters the GaAsSb band edge energies are determined over the 0.0 to 0.5 Sb mole fraction range. The effect of band alignment on electron–hole overlap and wavelength extension is discussed. [Copyright &y& Elsevier]

GaTe was used as a dopant source in molecular beam epitaxy to grow n-type AlSb, GaSb, InAs, and GaAs. Carrier density was independent of host material and growth temperature between 350°C and 550°C. Calibrations based upon the binary results were applied to alloys of InAlAsSb for high-frequency transistor applications. Controlled doping of these alloys was achieved at growth temperatures of 350°C and 400°C. Growth of a nominally undoped GaAs layer immediately after use of the GaTe cell indicated no significant memory effects. [Copyright &y& Elsevier]

We applied InGaAsP/InAlAs strain compensated superlattice (SCSL) structure to the multiplication region of avalanche photodiode (APD) for the first time using gas-source molecular beam epitaxy. For the InGaAsP/InAlAs SCSL structure, material quality was evaluated by means of cross-sectional transmission electron microscope analysis and X-ray rocking curves. SCSL-APD device was fabricated and dark current property was also compared to normal InGaAsP/InAlAs superlattice avalanche photodiode (SL-APD). It was found that application of the SCSL structure to the multiplication layer in SL-APD improves the dark current property. [Copyright &y& Elsevier]

We investigated the effects of atomic hydrogen (H*) irradiation on native oxides of InN films by X-ray photoelectron spectroscopy, mass spectrometry, low-energy electron diffraction (LEED) and scanning electron microscopy. After H* irradiation, it was found that the higher-binding-energy side of the In4d peak drastically decreased and a clear (1×1) LEED pattern was observed. From these results, it is considered that H* irradiation is effective to remove native oxides on InN films with only small surface damage. [Copyright &y& Elsevier]

InN with a film thickness of 600 nm was grown on a (0 0 0 1) sapphire substrate using low-temperature-grown intermediate layers by radio frequency plasma-excited molecular beam epitaxy (RF-MBE). From SEM observation, it was found that InN films with uniform surface morphology were grown. The electron mobility at room temperature obtained in this study was 830 cm2/V s and the corresponding carrier density was 1.0×1019 cm-3. To our knowledge, this electron mobility is the highest value ever reported for single-crystal InN films. [Copyright &y& Elsevier]

Abstract: The structural and electrical properties of N- and In-polar InN films grown directly on substrates were investigated. The twist contribution of directly grown InN films, which was defined by the estimated X-ray rocking curve''s full-width at half-maximum (XRC''s FWHM) of InN (101¯0) reflection, varied considerably by at least 40arcmin for both N- and In-polar InN films, depending on growth conditions. In contrast, the tilt contribution, defined by the XRC''s FWHM of InN (0002) reflection, was roughly fixed at 1.5–2.5arcmin for N-polar InN films and 8–12arcmin for In-polar InN films. For samples with the same twist contribution, In-polar InN films had larger tilt contribution than N-polar InN films. Nevertheless, electrical properties of In-polar InN had much better properties than those of N-polar InN films. [Copyright &y& Elsevier]