Search

Abstract: We present calculations of carrier confinement characteristics in (Al y Ga1−y N/AlN)SLs/GaN/(In x Ga1−x N/GaN)MQW/GaN heterojunction structure in the presence of spontaneous and piezoelectrically induced polarization effects. The calculations were made using a self-consistent solution of the Schrödinger, Poisson, potential and charge balance equations. An optimization of In x Ga1−x N/GaN multiquantum-well (MQW) was made firstly including thickness of GaN channel, InGaN, and indium composition of In x Ga1−x N in order to increase carrier density and mobility, and the influence of pairs of AlGaN/AlN superlattices (SLs) and InGaN/GaN MQWs on structure was discussed. Theoretical calculations clearly indicate that the two-dimensional electron gas (2DEG) sheet carrier density in designed heterostructure is greatly increased due to the enhancing of carrier confinement compared to those in conventional AlGaN/GaN one at the similar Al composition. Furthermore, the calculated carrier distribution shows that carrier mobility will be improved by reducing interface roughness and alloy disorder scattering in designed heterostructure. [Copyright &y& Elsevier]

Abstract: In this article, the significant effect of a thin gate thermal oxide layer on InGaP/InGaAs doping-channel field-effect transistors (DCFETs) is first demonstrated. When compared to the conventional InGaP/InGaAs DCFET, the device with the gate thermal oxide layer exhibits a higher gate turn-on voltage and nearly voltage-independent transconductances as the gate-to-source is biased form −0.75V to 0V, while the maximum transconductance is lower. Experimentally, the transconductance within 90% of its maximum value for gate voltage swing is 1.63V in the gate-oxide device, which is greater than that of 1.35V in the device without the gate thermal oxide layer. Furthermore, it maintains a high drain current level at negative gate bias in the gate-oxide device, which can be attributed that the thermal oxide layer with a considerably large energy gap absorbs more of gate negative voltage and the influence of negative voltage on the gate depleted thickness is relatively slight. [Copyright &y& Elsevier]

Abstract: The performance of GaN based devices could possibly be improved by utilizing the good p-type properties of GaP layer and it provides the possibility of the integration of InAlGaN and AlGaInP materials to produce new devices, if high quality GaP compounds can be grown on III-nitride compounds. In this paper, the growth of GaP layers on GaN by metalorganic chemical vapor deposition (MOCVD) has been investigated. The results show that the GaP low temperature buffer layer can provide a high density of nucleation sites for high temperature GaP growth. Using a 40nm thick GaP buffer layer, a single crystal GaP layer, whose full-width at half-maximum of the (111) plane measured by double crystal X-ray diffraction is 580″, can be grown on GaN. The V/III ratio plays an important role in the GaP layer growth and an appropriate V/III ratio can improve the quality of GaP layer. The GaP:Mg layer with hole carrier concentration of 4.2×1018 cm−3 has been obtained. [Copyright &y& Elsevier]

Abstract: The 32 possible kinds of B3C10N3 monolayer were built following the constraints derived from previous experiments. Conducting and semiconducting monolayer were found after geometry optimization by local density approximation (LDA) in CASTEP. By stacking monolayer with relatively lower energies in AB sequence, different B3C10N3 layer structures were built. According to the calculation results, structural and electronic properties for two typical structures, conducting and semiconducting B3C10N3 were investigated. [Copyright &y& Elsevier]

Abstract: A systematic study of the crystallographic and electrical/optical properties of MOVPE-grown InN was performed, and the factors that restrict the quality of MOVPE InN were elucidated. The quality of grown InN is highly dependant on the thermal decomposition of NH3 as a nitrogen source. At a lower growth temperature (~550°C) a shortage of active nitrogen, due to a lower decomposition rate of NH3, causes the formation of N vacancies in the grown InN. With increasing growth temperature, a more stoichiometric crystal is grown and the electrical/optical properties improve. At temperatures above 600°C, however, deterioration occurs at the N-face of In-polar InN near the substrate interface. This deterioration results in the formation of a porous layer during high temperature (~650°C) growth. There are a few evidences that show that the hydrogen produced by NH3 decomposition causes this degradation. Thus, improving the quality of MOVPE-grown InN by changing the growth temperature can be difficult. However, a short growth time at a high growth rate and a relatively high temperature is one effective way to solve this dilemma, and one can achieve carrier concentrations as low as 4×1018 cm−3 by growth at 650°C for 30min. [Copyright &y& Elsevier]

A theoretical and numerical analysis of the transmission of phase-modulated laser pulses through a thin film with excitonic nonlinearity is performed. It is shown that, by choosing the modulation law, one can efficiently control the optical nonlinearity of the film down to the inversion of the sign of nonlinearity. [ABSTRACT FROM AUTHOR]

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: A degradation mechanism in InGaP/GaAs heterojunction bipolar transistor (HBT) was investigated. The current gain of the HBT grown at a V/III ratio of 0.7 for the base layer decreased when annealed at 670°C. The samples grown at V/III ratios >1.0 showed constant photoluminescence intensity independent of annealing temperature, indicating that high thermal stability is obtained, while the V/III ratios <1.0 showed significant reductions by thermal annealing. Infrared (IR) absorption measurement revealed that the intensity of C–H and C2–H complexes in carbon-doped GaAs decreased when annealed at >550 and 650°C, respectively. We suggest that the decomposition of the C2–H complex creates defect centers, which lead to the current gain reduction. [Copyright &y& Elsevier]

Abstract: The GaInP/GaInAs/Ge triple junction (3J) space cell technology is nearing practical achievable conversion efficiency limits of ∼30% under 1-sun AM0 illumination. We present solar cell device-modeling results that indicate the GaInP/GaAs/GaInAs architecture with optimal bandgap energies will produce an additional 4% output power relative to the present GaInP/GaInAs/Ge 3J space cell technology. We have grown the GaInP/GaAs/GaInAs 3J cell on GaAs substrates in an inverted fashion incorporating a 1.0eV metamorphic GaInAs cell, using metal-organic vapor-phase epitaxy (MOVPE) in a production scale reactor. Nearly strain-free growth of the metamorphic GaInAs cell was verified by high-resolution X-ray reciprocal space mapping. From cathodoluminescence (CL) data, the 1.0eV metamorphic GaInAs cell threading dislocation density (TDD) is estimated to be 5×106 cm−2. With this level of TDDs we are able to produce a 3J IMM cells with a one-sun AM0 efficiency of 32%. In addition, external quantum efficiency (EQE) data suggests that improvements in current matching of the subcells will result in an AM0 efficiency of 33%. [Copyright &y& Elsevier]

Using the Hall method, regularities of Te doping of GaSb grown by the Czochralski method and by liquid-phase epitaxy (LPE) are studied. Optimum epitaxial conditions that enable the growth of Te-doped GaSb layers with higher carrier mobilities than the bulk Czochralski-grown GaSb are determined. Possibilities of improvement of output parameters of photoconverters obtained by diffusion of Zn into n-GaSb from the gas phase and by LPE are discussed. [ABSTRACT FROM AUTHOR]

Abstract: In this study, we investigated frequency dependent electrical and dielectric properties of metal–semiconductor (MS) structures using capacitance–voltage (C–V) and conductance–voltage (G/ω–V) characteristics in the frequency range 100kHz–10MHz in the room temperature. The dielectric constant (ε′), dielectric loss (ε″), dielectric loss tangent (tan δ) and ac electrical conductivity (σ ac) were calculated from the C–V and G/ω–V measurements and plotted as a function of frequency. In general, ε′, ε″ and tan δ values decreased with increasing the frequency, while σ ac increased with increasing frequency. Furthermore, the voltage and frequency dependence of series resistance were calculated from the C–V and G/ω–V measurements and plotted as functions of voltage and frequency. The distribution profile of R S–V gives a peak in the depletion region at low frequencies and disappears with increasing frequencies. Also, series resistance values decreased with increasing frequency. The experimental results show that both frequency dependent electrical and dielectric parameters were strongly frequency and voltage dependent. [Copyright &y& Elsevier]

Abstract: Magneto-conductance fluctuations serve as the traditional method for investigating the dynamics of electrons as they flow through solid-state materials. Generated by electron wave interference, their spectral content is critically sensitive to the precise scattering configurations in the material. In this paper, we exploit this sensitivity to study the electron dynamics in the diffusive regime of semiconductors where the dynamics are determined by material-induced scattering. We show that the spectral content of the fluctuations measured on diffusive n+GaAs wires and quasi-ballistic AlGaAs/GaAs wires follow a fractal scaling behaviour similar to that previously observed in ballistic semiconductors. We present an interpretation based on chaotic dynamics generated by the material-induced disorder. [Copyright &y& Elsevier]

Abstract: The electron energy spectrum of quantum rings under applied magnetic fields is calculated, taking into account the existence of rough interfaces between materials. The Schrödinger equation, within the effective mass approximation, is solved in a realistic model, not limited to small perturbations. Our numerical results show that the existence of roughness on the ring surface modifies significantly the electron confinement energy, lifts the degeneracy of the electron angular momentum transition points of the Aharonov–Bohm oscillations, and in some special cases, it can even suppress the ground state energy oscillations. [Copyright &y& Elsevier]

Abstract: AlGaInP/GaInP quantum well intermixing phenomena induced by Zn impurity diffusion at 540°C were studied using room-temperature photoluminescence (PL) spectroscopy. As the diffusion time increased from 40 to 120min, PL blue shift taken on the AlGaInP/GaInP quantum well regions increased from 36.3 to 171.6meV. Moreover, when the diffusion time was equal to or above 60min, it was observed firstly that a PL red shift occurred with a PL blue shift on the samples. After detailed analysis, it was found that the red-shift PL spectra were measured on the Ga0.51In0.49P buffer layer of the samples, and the mechanism of the PL red shift and the PL blue shift were studied qualitatively. [Copyright &y& Elsevier]

Abstract: The competition between surface/interface and intrinsic anisotropies yields a number of specific reorientation effects and strongly influences magnetization processes in diluted magnetic semiconductors as (Ga,Mn)As and (In,Mn)As. We develop a phenomenological theory to describe reorientation transitions and the accompanying multidomain states applicable to layers of these magnetic semiconductors. It is shown that the magnetic phase diagrams of such systems include a region of four-phase domain structure with four adjoining areas of two-phase domains as well as several regions with coexisting metastable states. We demonstrate that the parameters of isolated domain walls in (Ga,Mn)As nanolayers are extremely sensitive to applied magnetic field and can vary in a broad range. This can be used in microdevices of magnetic semiconductors with pinned domain walls. For (Ga,Mn)As epilayers with perpendicular anisotropy the geometrical parameters of domains have been calculated. [Copyright &y& Elsevier]

Abstract: In this letter, Raman spectra for a series of (Ga, Mn)N samples with different Mn concentration grown by MOCVD have been investigated. A new vibrational mode at 577 cm−1 obtained is assigned to the local vibrational mode (LVM) of Mn substituting the Ga site. Another mode at 667 cm−1 arises from vibrational mode of nitrogen vacancies-related defects. It is found that Mn doping increases the lattice disorder and other built-in defects such as the nitrogen vacancies. The room temperature ferromagnetism is not only dependent on the substitutional Mn content but also strongly related to these lattice disorder and negative defects in (Ga, Mn)N films. [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: 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: GaN films and multiple quantum well (MQW) LED wafers were grown by a metal-organic chemical vapor deposition (MOCVD) system under low pressure. The growth process was in situ investigated by normal incidence reflectance measurement. The properties of GaN layers were measured by double crystal X-ray diffraction (DCXRD), Hall method and photoluminescence, respectively. The results revealed that not only the properties of GaN layers but also the properties of the blue MQW LED wafers were obviously influenced by the growth mode in the initial stage of high-temperature (HT) GaN growth. The full-width at half-maximum (FWHM) values of the DCXRD peaks, as well as the background carrier concentrations, were obviously decreased when the 3D growth time of HT GaN at the initial stage was prolonged properly. This implies that the dislocation density in GaN films decreased. Moreover, the LED properties, such as the leakage current and the LED output power, would be largely improved if the 3D growth time of HT GaN in the initial stage was proper. [Copyright &y& Elsevier]

Abstract: This paper reports on in situ passivation studies of GaAlN/GaN High electron mobility transistors (HEMT) structures grown by low-pressure metalorganic vapour phase epitaxy (LP-MOVPE) on sapphire and silicon carbide substrates. GaN, GaAlN, AlN and AlN/GaN superlattice (SL) layers have been deposited at low temperature (LT) by LP-MOVPE on the surface of GaAlN/GaN HEMT structures. These high resistivity LT materials behave like dielectric films and seem very promising insulating materials for HEMT applications. Growth optimisation of GaAlN/GaN HEMT structures with the different LT cap layers mentioned has been carried out. The critical impact of the induced strain on the physical properties of the LT cap layer/GaAlN/GaN HEMT structures was identified and studied using high-resolution X-ray diffraction (HR-XRD), atomic force microscopy (AFM), C–V and eddy current measurements. HEMT structures based on LT-GaN and LT-AlN/GaN SL cap layers were found to have the best structural and electrical properties in term of surface roughness or sheet resistance of the 2DEG. Devices were made on these two samples in order to validate the statement. The static characteristics of these devices such as maximum drain current I dss and transconductance g m are comparable to those obtained on standard structures and the pinch-off voltage is shifted in good agreement with the thickness of the related insulating layers as observed by C–V measurements on wafers. Such observations indicate that LT cap layers deposited by MOCVD can be used as dielectric films to passivate the surface states of HEMT wafers. [Copyright &y& Elsevier]

Abstract: We investigated GaN buffer layers grown on Si substrates using a multi-wafer metalorganic vapor-phase epitaxy (MOVPE) system for 4-in five wafers (5×4″) growth in order to obtain field-effect transistors (FETs) with high breakdown voltages. It was confirmed that GaN films with smooth surfaces and without any cracks were obtained. To obtain high-resistive GaN buffer layers, C-doping was carried out by controlling the V/III ratio and the growth pressure. The breakdown voltage of the buffer layer was strongly correlated with the C concentration. As a result, the breakdown voltage was over 800V when the C concentration was about 8E18cm−3. We also fabricated a heterojunction FET (HFET) using an AlGaN/GaN heterostructure on a C-doped GaN buffer layer. The breakdown voltage of the FET in the off state was over 500V and the maximum drain current of the FET was over 300mA/mm. It was thus confirmed that an AlGaN/GaN HFET with a high-resistive buffer layer on a 4-in Si substrate could be obtained. [Copyright &y& Elsevier]

Abstract: AlGaN/GaN high electron mobility transistors (HEMTs) have been grown on 4 and 6in Si(111) substrates by metal organic vapor phase epitaxy (MOVPE). A record sheet resistance of 256Ω/□ has been measured by contactless eddy current mapping on 4in silicon substrates. The wafer also shows an excellent uniformity and the standard variation is 3.6Ω/□ over the whole wafer. These values were confirmed by Hall–Van der Pauw measurements. In the 2DEG at the AlGaN/GaN interface, the electron mobility is in the range of 1500–1800cm2/Vs and the electron density is between 1.3×1013 and 1.7×1013 cm−2. The key step in obtaining these results is an in-situ deposited Si3N4 passivation layer. This in-situ Si3N4, deposited directly after AlGaN top layer growth in the MOVPE reactor chamber, not only prevents the stress relaxation in AlGaN/GaN hetero-structures but also passivates the surface states of the AlGaN cap layer. HEMT transistors have been processed on the epitaxial structures and the maximum source–drain current density is 1.1A/mm for a gate-source voltage of 2V. The current collapse is minimized thanks to in-situ Si3N4. First results on AlGaN/GaN structures grown on 6in Si(111) are also presented. [Copyright &y& Elsevier]

Abstract: In this paper, we investigate theoretically the electron transport in AlGaN/GaN single-barrier and in AlGaN/GaN/AlGaN double-barrier heterostructures, aimed to operate as high-power and high-temperature field-effect transistors. The presence of spontaneous and piezoelectric polarizations as well as the heterointerface polarity are evoked and taken into account in the modelling part. Delta-doping is used as a source of electrons for the channel quantum well. Calculations of the electron-band parameters are made by using self-consistent solutions of coupled Schrodinger–Poisson equations. It is found that the polarization fields act to significantly increase the two-dimensional sheet charge concentration. Moreover, the AlGaN/GaN heterostructures with higher Al compositions are found to be favourable for higher electron densities. On the other hand, the employment of a back doping with delta-shaped profiles is shown to improve further the electrical behaviour of the field-effect transistors studied. [Copyright &y& Elsevier]

Using the thermopower method (Seebeck effect), the semiconductor-metal transition that occurs in gallium arsenide single crystals of n and p types at ultrahigh pressures P above ∼11–18 GPa has been studied. It has been found that the transition in n-type samples begins at lower pressures. In the region of the semiconductor-metal phase transition, features have been observed on the thermopower dependences S( P). These features indicate that lattices intermediate between the initial semiconductor structure of zinc blende and the Cmcm high-pressure orthorhombic metallic phase are formed. By analogy with ZnTe, one intermediate phase (semiconductor with hole conductivity) is suggested to have the cinnabar structure and the second intermediate phase (semimetallic with electron conductivity) possibly has the SC16 structure. A model of the semiconductor-metal transition is discussed. The behavior of the thermoelectric properties in GaAs under pressure is compared with the behavior of these properties in other ANB8−N semiconductors, which also undergo the transition to the metallic state. [ABSTRACT FROM AUTHOR]

Abstract: The surface effects, the (NH4)2S and low-temperature-deposited SiN x passivations of InP-based heterostructure bipolar transistors (HBTs) have been investigated. The surface recombination current of InP-based HBTs is related to the base structures. The (NH4)2S treatment for InGaAs and InP removes the natural oxide layer and results in sulfur-bonded surfaces. This can create surface-recombination-free InP-based HBTs. Degradation is found when the HBTs were exposed to air for 10 days. The low-temperature-deposited SiN x passivation of InGaAs/InP HBTs causes a drastic decrease in the base current and a significant increase in the current gain. The improvement in the HBT performance is attributed to the low deposition temperature and the effect of N2 plasma treatment in the initial deposition process. The SiN x passivation is found to be stable. S/SiN x passivation of InGaAs/InP HBTs results in a decrease in the base current and an increase in the current gain. The annealing process can cause the base current to decrease further and the current gain increase. [Copyright &y& Elsevier]

Abstract: This paper reports on a four-terminal dual-emitter heterojunction phototransistor (4T-DEPT) with a base biased by a current source in comparison with a three-terminal dual-emitter heterojunction phototransistor (3T-DEPT). While only voltage can be used to tune the optical performance of the 3T-DEPT, voltage- and current-control modes are considered for the 4T-DEPT. One emitter (E2) serves as the voltage (V E21)-controlled terminal at a fixed base biasing current while the other one (E1) is at the ground state. On the other hand, the base terminal controls the operation by applying an additional current (I Bdc) bias when the V E21 is constant. Therefore, voltage- and current-dependent characteristics will be detailed. Four operating regions exist in the voltage-dependent characteristics for both 3T- and 4T-DEPTs: negative-saturation, negative-tuning, positive-tuning, and positive-saturation regions. When the 4T-DEPT operates at the bias condition of V E21 =0.4V, I Bdc =0.001μA, and the incident optical power (P in) of 0.423μW, it shows the maximum current-dependent current-tuning efficiency and gain-tuning efficiency of 21.40 and 73.87μA−1, respectively. In addition to the power- and voltage-tunable optical gains, a current-tunable one is also available in the 4T-DEPT. [Copyright &y& Elsevier]

Abstract: Schottky barrier contact using three different metal (Zr, Ti, Cr and Pt) and Ohmic contact using Ni were made on same epitaxial growth layer of p-GaN. Measurements were carried out using current–voltage–temperature (I–V–T) in the range of 27–100°C. Under forward bias and room-temperature (RT), the ideality factors (η) were determined to be 2.38, 1.82, 1.51 and 2.63, respectively, for Zr, Ti, Cr and Pt. The Schottky barrier height (SBH) and effective Richardson coefficient A ** were measured through modified Norde plot as one of the analysis tools. Barrier heights of 0.84, 0.82, 0.77 and 0.41eV for Zr, Ti, Cr and Pt, respectively, were obtained from the modified Norde plot. Schottky barrier heights of Zr, Ti, or Cr/p-GaN were also measured through activation energy plot, and determined to be in the same range (∼0.87eV) and Pt at 0.49eV. These results indicate that the Fermi level seems to be pinned due to the value of slope parameter (S) was very low (S =−0.25). [Copyright &y& Elsevier]

Abstract: A full-potential linearized augmented-plane-wave (FLAPW) method is used for the investigation of the electronic structure of a series group III–V semiconductors. The electronic structure of low-index clean GaAs surfaces and with thin overlayers of cesium is studied. We analyze Cs(O) coadsorption on the GaAs(001) surface as well as the influence of Sb on its electron and adsorption properties. [Copyright &y& Elsevier]

Abstract: A summary of experimental findings and theoretical modelling of micromagnetic properties of zinc-blende ferromagnetic semiconductor (Ga,Mn)As is presented. It is shown that the Zener p–d model explains quantitatively observed Curie temperatures in compensation free samples and that major strain-related effects are correctly accounted for, including the presence of the magnetization reorientation transition, observed as a function of hole concentration and temperature. It is evidenced that a presence of a small trigonal distortion could account for both the presence and properties of uniaxial in-plane magnetic anisotropy. [Copyright &y& Elsevier]

The energy and wave functions of localized electron states in a quantum well in a high magnetic field arbitrarily oriented with respect to the layers of the structure, and a high transverse electric field are studied. The situation where the quantum-confined energy and the Landau energy are close to each other is considered. The evolution of the spectrum with varying orientation of the magnetic field over the entire angle range is studied. [ABSTRACT FROM AUTHOR]

Abstract: A series of quaternary-diluted magnetic semiconductors, (In1− y Al y )1− x Mn x As, have been successfully grown on InP substrates by low-temperature molecular beam epitaxy. The (In0.52Al0.48)1− x Mn x As with x⩽0.11 were grown on a nearly lattice-matched In0.52Al0.48As buffer, while the (In1− y Al y )1− x Mn x As with a higher Mn content of 0.110.05, and the Curie temperature of ferromagnetic (In1− y Al y )1− x Mn x As increases with increasing Mn content. [Copyright &y& Elsevier]

Abstract: The impurity states in a narrow-gap semiconductor parabolic quantum dot in the presence of external extremely strong magnetic field are considered in adiabatic approximation framework. Moreover, the dispersion law for impurity electron is described by using the Kane''s two-band approximation. The effective one-dimensional equation describing the impurity electron''s state along the field is obtained. The analytical expressions for total and binding energies of impurity ground state are obtained. The dependences of total and binding energies of impurity on the value of magnetic field and on the size of quantum dot are investigated. [Copyright &y& Elsevier]

Abstract: The diffusion trapping model has been applied to understand the mechanism of slow positron annihilation in Si-doped compound semiconductors. The positron diffusion at the surface has been treated in terms of one dimensional diffusion equation. The trapping of positron has been considered in Ga monovacancies and negative ion vacancies. The Doppler broadening line shape parameter (S-parameter) and positron mean lifetime in Si-doped GaAs is calculated as a function of temperature for the temperature range 20–290K. The calculated results have been compared with the available experimental data (T. Laine, K. Saarinen, J. Makinen, P. Hautojarvi, Phys. Rev. B 62, (2000) 8058). The theoretical results show a good agreement with the experimental curve. The S-parameter vs temperature curve shows that the S-parameter is nearly constant up to 100K and then starts increasing and gets saturated at 200K. This has been found to be due to the increase in the monovacancy concentration. [Copyright &y& Elsevier]

Abstract: Several research groups have been actively pursuing antimonide-based electronic devices in recent years. The advantage of narrow-bandgap Sb-based devices over conventional GaAs- or InP-based devices is the attainment of high-frequency operation with much lower power consumption. This paper will review the progress on three antimonide-based electronic devices: high electron mobility transistors (HEMTs), resonant tunneling diodes (RTDs), and heterojunction bipolar transistors (HBTs). Progress on the HEMT includes the demonstration of Ka- and W-band low-noise amplifier circuits that operate at less than one-third the power of similar InP-based circuits. The RTDs exhibit excellent figures of merit but, like their InP- and GaAs-based counterparts, are waiting for a viable commercial application. Several approaches are being investigated for HBTs, with circuits reported using InAs and InGaAs bases. [Copyright &y& Elsevier]

Abstract: In this paper, we present an experimental study of the thermal emission and band-filling effects on the rise time in high-quality InGaAs/InAs/GaAs quantum dots emitting at 1.2μm at 10K. At excitation density of 104Wcm−2, the photoluminescence rise time, which is dominated by the relaxation time, of the ground and first excited states are independent of temperature (40ps). At excitation density of 5600Wcm−2 the ground (first excited) state photoluminescence rise time varies from 90ps (110ps) at 10K to 40ps (70ps) at 160K. This behavior is attributed to the band-filling and the thermal emission effects on the efficiency of the relaxation. [Copyright &y& Elsevier]

Abstract: We have prepared small Au/n-GaAs Schottky barrier diodes (SBDs) using e-beam lithography (EBL), and obtained their effective barrier heights (BHs) and ideality factors from current–voltage (I/V) characteristics, which were measured using a conducting probe atomic force microscope (CP-AFM). Although the diodes were all identically prepared, there was a diode-to-diode variation: the effective BHs ranged from 0.795eV to 0.836eV, and the ideality factor from 1.025 to 1.101. Lateral homogeneous BHs were computed from the observed linear correlation between BH and ideality factor using the method of Schmitsdorf et al. [Schmitsdorf RF, Kampen TU, Mönch W. J Vac Sci Technol B 1997;15(4):1221]. These homogeneous BHs were also obtained from the fit to the experimental I/V characteristics of the current through a “patchy” diode. From our model, the barrier height in the patches and their diameter could be determined. It are however the homogeneous BHs which should be used to make theories of the physical mechanisms responsible for the Schottky barrier height of the metal–semiconductor combination considered. [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: Future colliders such as NLC and JLC will require a highly polarized macropulse with charge that is more than an order of magnitude beyond that which could be produced for the SLC. The maximum charge from the SLC uniformly doped GaAs photocathode was limited by the surface charge limit (SCL). The SCL effect can be overcome by using an extremely high () surface dopant concentration. When combined with a medium dopant concentration in the majority of the active layer (to avoid depolarization), the surface concentration has been found to degrade during normal heat cleaning (1h at ). The Be dopant as typically used in an MBE-grown superlattice cathode is especially susceptible to this effect compared to Zn or C dopant. Some relief can be found by lowering the cleaning temperature, but the long-term general solution appears to be atomic hydrogen cleaning. [Copyright &y& Elsevier]

Abstract: This paper reports on the LP-MOCVD growth optimisation of GaAlN/GaN heterostructures grown on silicon carbide substrates for HEMT applications, and on the first device performances obtained with these structures. The critical impact of some growth parameters on the physical properties of the GaAlN/GaN epilayers has been identified and studied using high-resolution X-ray diffraction, AFM, and sonogauge measurements. SiC substrates from different suppliers were evaluated and their influence on the physical properties of the GaAlN/GaN HEMT structures were investigated. We show that the static characteristics of the devices such as maximum drain current Idss or pinch-off voltage are correlated with the nucleation layer composition ( GaN or GaAlN) of the HEMT structure and with the defect density of the SiC substrate. A maximum drain current Idss around 1A/mm and a pinch-off voltage of -5V have been measured for devices with a gate length of 0.3μm and a GaN nucleation layer, to be compared to an Idss up to 1.3A/mm obtained for devices with the same geometry but with a GaAlN nucleation layer. characteristics measured under pulsed measurements have also evidenced a clear impact of the nucleation layer composition on the trap density in the GaAlN/GaN HEMT structure. The first devices related to HEMT wafers with GaN nucleation layers were measured at 10GHz using a load pull system. They show a CW output power in excess of 2.8 W/mm for a gate length of 0.5μm, while devices related to HEMT wafers with GaAlN nucleation layer exhibit output power up to 4W/mm at 10GHz. [Copyright &y& Elsevier]

Self-assembled InAs quantum dots were grown on (001) orientated Si substrates by molecular beam epitaxy. Growth condition dependence of dot formation was studied. The evolution of size and shape of quantum dots with InAs coverage was examined using plan-view and cross-section transmission electron microscopy. Dot formation started at below 1 monolayer (ML) of InAs coverage, indicating Volmer–Weber growth mode. Dot size and density grew with increasing InAs coverage up to 0.7 ML. Dot density was observed to be strongly dependent on arsenic (As) beam equivalent pressure (BEP). A decrease of As BEP from 9.2×10-6 to 1.2×10-7torr resulted in an increase in dot density from 4.3×109 to 1.8×1011cm-2 at a constant InAs coverage of 0.7ML. Further increase in InAs coverage led to a clear broadening of dot size distribution and a slight decrease in dot density, presumably due to coarsening. [Copyright &y& Elsevier]

We investigate the effect of the longitudinal-optical phonon field on the binding energies of excitons in quantum wells, well-wires and nanotubes based on ionic semiconductors. We take into account the exciton–phonon interaction by using the Aldrich–Bajaj effective potential for Wannier excitons in a polarizable medium. We extend the fractional-dimensional method developed previously for neutral and negatively charged donors to calculate the exciton binding energies in these heterostructures. In this method, the exciton wave function is taken as a product of the ground state functions of the electron polaron and hole polaron with a correlation function that depends only on the electron–hole separation. Starting from the variational principle we derive a one-dimensional differential equation, which is solved numerically by using the trigonometric sweep method. We find that the potential that takes into account polaronic effects always give rise to larger exciton binding energies than those obtained using a Coulomb potential screened by a static dielectric constant. This enhancement of the binding energy is more considerable in quantum wires and nanotubes than in quantum wells. Our results for quantum wells are in a good agreement with previous variational calculations. Also, we present novel curves of the exciton binding energies as a function of the wire and nanotubes radii for different models of the confinement potential. [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]

We examined the dependence of hydrogen passivation in carbon-doped GaAsSb grown by metal-organic chemical vapor deposition (MOCVD) under various growth conditions and found that the carbon acceptors in carbon-doped GaAsSb can be passivated by hydrogen under some growth conditions, contrary to previous reports. The ratio between the hydrogen-passivated-carbon concentration, [C–H], and total carbon concentration, [C], in carbon-doped GaAsSb was smaller than that in carbon-doped GaAs and considerably smaller than that in carbon-doped InGaAs. This is apparently due to differences in the ionicity of the covalent bonds in the carbon-doped crystals and the location of the stable sites of carbon atoms. We also found that hydrogen passivation of carbon acceptors is closely related to the growth temperature. As the growth temperature is increased, the number of hydrogen-passivated carbon acceptors decreases more rapidly than the total number of carbon acceptors. As a result, carbon-doped GaAsSb with almost complete suppression of hydrogen passivation can be grown at temperature above 530°C. Using a high-temperature ambient apparently reduces the incorporation efficiency of hydrogen atoms, so that the hydrogen concentration passivating carbon acceptors is reduced to a negligible concentration. [Copyright &y& Elsevier]

Effects of V/III ratio on heavily Si doped InGaAs and InP were studied using low pressure metalorganic chemical vapor deposition (LP-MOCVD) at a growth temperature of 550°C. In InGaAs, as the V/III ratio decreases from 256 to 64, the carrier concentration increases from 3.0×1018 to 5.8×1018 cm−3; and the lattice mismatch of InGaAs to InP was observed to vary from −5.70×10−4 to 1.49×10−3. In InP, when the V/III ratio decreases from 230 to 92, the same trend as that in Si doped InGaAs was observed that the carrier concentration increases from 9.2×1018 to 1.3×1019 cm−3. The change of AsH3 was found to have stronger effect on Si incorporation in InGaAs at lower growth temperature than at higher growth temperature. [Copyright &y& Elsevier]

In this paper, Al/AlN/Si(1 1 1) metal–insulator–semiconductor (MIS) structure has been fabricated and their interfacial properties have been investigated using capacitance–voltage techniques. The dielectric constant of AlN was found to vary from 5.01 to 8.67 with the frequency decreasing from 1 MHz to 50 Hz due to the existance of a transition zone between AlN and Si substrate which is not forbidden to the electronics. The distribution of the interface states in the interface was extracted from the frequency-dependent capacitance–voltage characteristics of the MIS structure. The interface state density Dit in the silicon forbidden band gap was in the order of 1012 eV−1 cm−2 and the time constant was about 10−5 s through analyzing the capacitance as a function of frequency. [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]

Abstract: A new method to test the hole concentration of p-type GaN is proposed, which is carried out by analyzing the spectral response of p–n+ structure GaN ultraviolet photodetector. It is shown that the spectral response of the photodetector changes considerably with reversed bias. It is found that the difference between photodetector''s quantum efficiency at two wavelengths, i.e. 250 and 361nm, varies remarkably with increasing reversed bias. According to the simulation calculation, the most characteristic change occurs at a reversed voltage under which the p-GaN layer starts to be completely depleted. Based on this effect the carrier concentration of p-GaN can be derived. [Copyright &y& Elsevier]