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The chemical reaction products of elemental sulfur (S), selenium (Se), and molecular hydrogen (H2) at high pressures and room temperature are probed by Raman spectroscopy. Two known compounds H2S and H2Se can be synthesized after laser heating at pressures lower than 1 GPa. Under further compression at room temperature, an H2S–H2Se and an H2S–H2Se–H2 van der Waals compounds are synthesized at 4 GPa and 6 GPa, respectively. The later is of guest–host structure and can be identified as (H2S) x (H2Se)(2−x)H2. It can be maintained up to 37 GPa at least, and the stability of its H2Se molecules is extended: the H–Se stretching mode can be detected at least to 36 GPa but disappears at 22 GPa in (H2Se)2H2. The pressure dependence of S–H and Se–H stretching modes of this ternary compound is in line with that of (H2S)2H2 and (H2Se)2H2, respectively. However, its hydrogen subsystem only shows the relevance to (H2S)2H2, indicating that this ternary compound can be viewed as H2Se-replaced partial H2S of (H2S)2H2.

Used Al-13wt%Si alloy was as raw material, the influence mechanism of Al-Sr, Al-P and Al-RE ternary compound modifier was studied by casting technology. The effects of P, Sr and RE modification on Al-13wt% Si were studied by metallographic microscope, scanning electron microscope and X-ray. The effects of the addition order and amount of modifier on the microstructure of Al-13wt% Si were investigated The results show that compared with a single modifier, P + RE + Sr ternary composite modifier has more obvious modification effect on eutectic silicon in Al-13%Si alloy: the microstructure of different morphology can be obtained by using different amount and order of adding modifier. When the amount and order of modifier are 0.5wt%Sr, 0.7wt%P, 1.5wt%RE,the eutectic silicon with small size and uniform distribution can be obtained. Eutectic silicon consists of 70 μm, the slender lamella is refined to 5 μm.

Ternary compound Cu2SnS3 (CTS) thin films were synthesized using two simple and non-vacuum processes: chemical spray pyrolysis and rapid thermal annealing (RTA). The crystal quality of CTS films improved and the band tailing, shown in Tauc's plot, tended to vanish after annealing in a nitrogen atmosphere using RTA. Although ethanol was used as a solvent in the spray pyrolysis, the CTS film was not contaminated by carbon and oxygen. The bandgap of CTS was changed via sulfurization. The optimization of the RTA process affected the composition of the CTS thin films, modifying material defects and improving the crystal quality. These results represent the initial step toward the practical application of CTS solar cells using an inexpensive fabrication process.

Using Rode's iterative method, we have investigated the semi-classical transport properties of the n-type ternary compound AlGaAs2. Four scattering mechanisms have been included in our transport calculation, namely, ionized impurity, piezoelectric, acoustic deformation and polar optical phonon (POP). The scattering rates have been calculated in terms of ab initio parameters. We consider AlGaAs2 to have two distinct crystal geometries, one in tetragonal phase (space group: [Formula: see text]), while the other one having body centered tetragonal crystal structure (space group: [Formula: see text]). Higher electron mobility has been observed in the body centered tetragonal phase, thereby making it more suitable for high mobility device application, over the tetragonal phase. In order to understand the differences in electron mobility for these two phases, curvatures of the E-k dispersion of the conduction bands for these phases have been compared. At room temperature, the dominant contribution in electron mobility was found to be provided by inelastic POP scattering. We have also noted that mobility is underestimated in relaxation time approximation compared with the Rode's iterative approach.

A method for forming thin films of the Cu2SnS3 compound homogeneous in phase composition for use in solar cell devices is proposed. The Cu-Sn alloy layers deposited by thermal spraying in vacuum were annealed in sulfur vapor in a graphite chamber of the quasi-closed volume type. Using X-ray phase analysis, the optimal conditions for the formation of Cu2SnS3 films homogeneous in phase composition were found: annealing temperature 450 °C, sulfur vapor pressure ∼ 0.2 torr. The sulfide layers obtained in this way in their elemental composition correspond to the Cu2SnS3 compound stoichiometry. Cu2SnS3 films have an optical band gap of 1 eV, and the absorption coefficient in the visible region of the spectrum is 2·105 cm –1.

The effects of adding a large quantity of Li on the microstructure and solidified precipitation behavior of an as-cast Al–Mg–Si alloy was investigated by thermodynamic calculation and microstructural characterization. The addition of Li substantially changed microstructural features and solidified precipitate phases of the Al–Mg–Si alloy. According to thermodynamic calculations, in addition to the Mg2Si phase, the second phases of Li-containing alloy also included δ-AlLi and Al2LiMg precipitates, in contrast to the base Al–Mg–Si alloy. Unusually, the Al2LiMg phase was found even when the content of Mg was below 2 wt.%. The content, quantity, and distribution of the second phases in different alloys were revealed by optical microscopy, scanning electron microscopy and X-ray diffraction analysis synthetically. AlLiSi ternary compound was only found in the alloy with excess Si content. In addition, transmission electron microscopy observations were used to characterize crystal structures of the Li-containing phases. The results showed that a δ'-Al3Li metastable phase, instead of a δ-AlLi phase, was precipitated because of the occurrence of non-equilibrium solidification.

The (Zr1-x T x )3Al3C5 (T = Hf, Nb, and V) series can be potential candidates to extend the domain of MAX phases. In this work, the structures and properties of (Zr1-x T x )3Al3C5 (T = Hf, Nb, and V) are studied using first-principles calculations. The obtained structural parameters are in good accordance with previously reported data in the literature. Based on the phase stability investigations, the potentially stable layered (Zr1-x T x )3Al3C5 (T = Hf, Nb, and V) solid solutions are proposed, which confirms that Zr3Al3C5 and Hf3Al3C5 can be synthesized. The substitution, especially with group VB transitional metals, endows layered (Zr1-x T x )3Al3C5 series with greatly enhanced mechanical and thermal properties. It is indicated that the bulk modulus B of all the three systems increase with increasing substitution concentration x. A significant increase in the ratio of bulk modulus to shear modulus, B/G, is found with increasing V concentration, which corresponds to the improved ductility. Moreover, solid solutions with V substitution, (Zr1-x V x )3Al3C5, yield a larger effect on thermal conductivity with respect to x, indicating flexible modulation of the thermal conductivity of (Zr1-x V x )3Al3C5 by V substitution can be achieved, which may promote them as promising coating materials. The intrinsic mechanism involved in the enhancements of the mechanical and thermal properties were elucidated through thorough electronic band structure analysis. The difference in the electronic structure and bonding between Zr and T in (Zr1-x T x )3Al3C5 compounds are shown to account for the abnormal variations in their properties.

The n-type CdS is commonly used as a window layer on photovoltaic solar cells, but CdS has disadvantages such as a direct band gap of 2.4 eV that reduces the photons collection in the UV range. As an alternative solution, ZnS (with a band gap value between 3.6 eV and 3.9 eV) thin film was implemented in the photovoltaic devices as a buffer layer to try to solve the problem. ZnS thin films were grown by chemical bath deposition (CBD) technique and thermally treated on Air, Argon, Oxygen and CdCl2 atmospheres to improve their optoelectronic properties. CdCl2 treatment formed a ZnxCd1−xS ternary compound. In this work, physical properties of ZnS thin films as deposited and thermally treated were studied; on the other hand, ZnS/CdS and ZnxCd1−xS/CdS junctions are implemented in CdTe solar. Experimental and simulated I–V curves were fitted and analyzed.

InGaN blue light-emitting diodes (LEDs) were fabricated on a sapphire substrate with a ZnO nucleation layer that was deposited by the sol–gel method. Typical current–voltage (I–V) characteristics of the InGaN blue LEDs with a ZnO nucleation layer have a forward-bias voltage of 3.25 V at an injection current of 20 mA, and reverse currents of 2.33 × 10−8 and 5.91 × 10−7 A at reverse biases of 10 and 20 V, respectively. The InGaN blue LEDs have an ideality factor n of 1.27 at a forward bias of 1.8 V. The external quantum efficiency at an injection current of 20 mA was measured to be 12.82%. The light output power reached as high as 23.2 mW at a forward current of 100 mA.

x-cut Nd : MgO : LiNbO3 wafers are implanted with 3 MeV O+ ions at a dose of 6 × 1014 cm−2, directly using a photoresist mask consisting of a series of open stripes of width 10 µm. The extraordinary refractive index (RI) experiences positive changes with respect to the bulk after ion bombardment and post-implantation annealing; therefore, channel waveguide structures are formed in the implanted regions. The near field intensity distributions of the transverse-electric modes are obtained by an end-fire coupling arrangement. The modal simulation result shows the reasonableness of the reconstructed RI profiles, which is helpful in designing practical waveguide devices produced by the ion implantation technique.

The phase relations of the GdCo13−x Six system have been studied by means of scanning microscopy, microprobe analysis and x-ray diffraction. Single-phase samples GdCo9±δSi4∓δ (structure type LaFe9Si4 with space group I 4/mcm) ar ef ormed in a narrow composition range |δ| 0.2, where GdCo9Si4 forms as af ully ordered ternary compound. The magnetic properties of GdCo9Si4 have been investigated by ac susceptibility, magnetization, specific heat and resistivity measurements. These experiments reveal ferrimagnetism below about 47 K, which is analysed in terms of a two-sublattice molecular field model with a local moment Gd subsystem coupling antiparallel to the itinerant ferromagnetic Co 3d sublattice. The 3d–3d exchange of the latter is the driving force for the onset of long range magnetic order. The validity of the twosublattice model is demonstrated by high field measurements, showing that the ferrimagnetic coupling starts to break up at a lower critical field µ0 Hl � 27 T. The magnetic ground state of GdCo9Si4 has been analysed on a microscopic basis via LSDA electronic structure calculations. (Some figures in this article are in colour only in the electronic version)

InP-based InAlAs/InxGa1?xAs/InP high-electron-mobility transistors (HEMTs) with a symmetrically graded channel (SGC-HEMT) and an inversely graded channel (IGC-HEMT) were fabricated and studied. The SGC-HEMT exhibits better Hall, dc and RF characteristics than the IGC-HEMT because there are more electrons accumulated in the symmetrically graded channel. However, the IGC-HEMT has better thermal stability than the SGC-HEMT because the former has higher bandgap discontinuity at the channel/buffer heterojunction and less Coulomb scattering from a ?-doped layer. Furthermore, the IGC-HEMT sustains larger output power than the SGC-HEMT attributed to better breakdown characteristics. Therefore, HEMTs with the symmetrically graded and an inversely graded channel are suitable for high-speed and high-power applications, respectively.

A new compound with the same chemical composition as Li3AlB2O6 but with a different x-ray powder diffraction pattern as reported before was synthesized and studied experimentally by M. He, Chen X L et al (J. Solid State Chem. 163, 369 (2002)), but there lacks first principles study on the structure of it. Using conjugant gradient (CG) molecule dynamics (MD) simulation with a full relaxation of the atomic positions and of the shape and size of the cell, the structure of Li3AlB2O6 is studied from first principles. For the density functional, the local density approximation (LDA) and the generalized gradient approximation (GGA) forms are used respectively. Both the LDA and GGA results support the experimental structure of M. He et al. The result of MD simulation using GGA agrees with the experimental result much better. The energy bands are also studied, the band gap given by LDA and GGA are 5.65 eV, 5.34eV, respectively.

Wet-etching of amorphous Ge2Sb2Te5 films was studied by ICP and XPS spectrometries. It is thought that wet-etching arises from chemical etching that starts with bond breakages, oxidation of each element and subsequent dissolution of the resultant oxides. The Ge element debonds more easily from the Ge–Sb–Te matrix than the Te element, but Ge oxide is more stable than Te oxide. The Te element debonds more sluggishly than Ge, although Te oxide is quite unstable. As a result, Ge is the first leached element that dominates the etching process. Sb is the most difficult element to leach in Ge2Sb2Te5 thin films. Cells of phase-change random access memory (PRAM) were successfully manufactured using the wet-etching process, and studies of the switching properties revealed a low threshold voltage of 0.60 ± 0.15 V.

Based on perspectives of the development of semiconductor materials systems for high-power light-emitting diodes (LEDs), an illumination facility for greenhouse plant cultivation was designed with the dominating 640 nm photosynthetically active component delivered by AlGaInP LEDs and supplementary components from AlGaN (photothropic action, 455 nm) and AlGaAs (photosynthetic 660 nm and photomorphogenetic 735 nm) LEDs. Photosynthesis intensity, photosynthetic productivity and growth morphology as well as chlorophyll and phytohormone concentrations were investigated in radish and lettuce grown in phytotron chambers under the LED-based illuminators and under high-pressure sodium (HPS) lamps with an equivalent photon flux density. Advantages of the high-power LED-based illuminators over conventional HPS lamps, applicability of AlGaInP LEDs for photosynthesis and control of plant growth by circadian manipulation of a relatively weak far-red component were demonstrated.

Two-dimensional simulations of surface charge effects in AlGaN/GaN HEMT and GaN MESFET devices are performed. The influence of charges of different magnitude, sign and spatial distribution at the ungated surface on drain current characteristics is studied. We have found that positive and negative surface charges of the same magnitude produce very different modifications of drain current. The relative influence of polarization fields, surface charges and free hole accumulation at the top surface is considered and gives rise to the opposite behaviour in HEMT and MESFET devices. The implications of our study in current collapse and related dispersion effects in GaN FETs are discussed.

A series of RbxCs1−xAg4I5 (x = 0–1) thin films were grown by vacuum evaporation on NaCl crystal substrates at 350 K. The absorption spectra of these films were measured at 80 K in the wavelength range from 240 nm to 400 nm. It is shown that superionic conductor thin films of quaternary compound Rb0.5Cs0.5Ag4I5 and ternary compound RbAg4I5 can be obtained at x = 0.5–0.6 and x = 0.7–1, respectively. At x = 0.65, the combined compound film of the mixture of 30 mol% RbAg4I5 and 70 mol% Rb0.5Cs0.5Ag4I5 is presented. Then, based on the spectral positions of the A1 and A2 peaks, we determined that the Rb0.5Cs0.5Ag4I5 exciton coupling energy Rex is 0.21 eV, the forbidden zone width Eg is 3.82 eV and the exciton radius aex is 0.70 nm. Furthermore, the ionic conductivities of superionic conductor thin films of RbAg4I5 and Rb0.5Cs0.5Ag4I5 and their mixture film are investigated, respectively, in the temperature range 303 K–393 K.

We report on the temporal pulse response measurements of solar-blind AlxGa1-xN-based heterojunction p-i-n photodiodes. High-speed characterization of the fabricated photodiodes was carried out at 267 nm. The bandwidth performance was enhanced by an order of magnitude with the removal of the absorbing p+ GaN cap layer. 30 μm diameter devices exhibited pulse responses with ∼70 ps pulse width and a corresponding 3 dB bandwidth of 1.65 GHz.

Circular geometry InGaP/GaAs double heterojunction bipolar transistors with spacings of 94.5, 44.5, 19, 10.5 and 5.5 µm between the base metal and emitter mesa were fabricated and characterized. The measured Gummel plots showed a current gain of 50 for the 94.5 µm device. As the spacing decreases to 5.5 µm, the base current increases due to the extrinsic base surface recombination current at VBE = 0.9 V thus reducing the current gain to a value of 10. It was found that the use of Ti/Au over Au/Zn/Au base metallization schemes eliminates this recombination current component of the base thereby improving the current gain significantly to 100. With a novel scheme employed here termed the δ+-layer composite collector structure, the collector leakage current was investigated.

New InP/InGaAs δ-doped heterojunction bipolar transistors have been successfully fabricated and demonstrated. The use of a δ-doped sheet between two undoped spacer layers more effectively eliminates the potential spike at the base–emitter junction and lowers the collector–emitter offset voltage. The maximum current gain and offset voltage of 455 (533) and 55 mV (33 mV) are observed, respectively, for the unpassivated (passivated) emitter device at room temperature. The base surface recombination current of the studied devices is also investigated in this paper. The studied devices are therefore promising for practical circuit applications.

Using material chip technology, large area n-on-p planar junctions with various boron implantation doses have been fabricated on an Hg1−xCdxTe (x = 0.291) film, similarly grown using molecular beam epitaxy, for the mid-infrared wavelength range. The current–voltage characteristics of p–n junctions have been measured on a cold stage at 77 K and an optimized ion implantation dose has been discovered. Zero bias resistance of all the junctions has been calculated and shows distinct dependence upon the boron implantation doses.

It has been demonstrated experimentally that the electron drift mobility of a two-dimensional electron gas in the channel of AlGaN/GaN metal-oxide-semiconductor heterostructure field effect transistors (MOSHFETs) may be appreciably higher than that in the conventional AlGaN/GaN HFETs for structures with a thin (10 nm) AlGaN barrier layer. For the conventional AlGaN/GaN heterostructures with barrier thickness of 10 nm, the maximum electron drift mobility in the 2D channel, μd, is equal to ~600 cm2 Vs−1, which is much lower than the Hall mobility measured with the same wafer (μH ≈ 1400 cm2 Vs−1). Introduction of a 7 nm thick SiO2 layer between the gate and the AlGaN layer to fabricate MOSHFETs leads to an increase in the electron drift mobility to μd ≈ 1400 cm2 Vs−1. Introduction of a SiO2 layer with the same thickness into the AlGaN/GaN heterostructures with relatively thick (25 nm) AlGaN barrier does not affect the maximum electron drift mobility in the channel of the heterostructures. The results obtained correlate well with published data on the influence of the barrier thickness on the high-power performance of AlGaN/GaN HFETs.

A polycrystalline stoichiometric sample of the ternary compound CdGa2Se4 was prepared and characterized by x-ray diffraction analysis. Lattice parameters were determined and compared with data in the literature. CdGa2Se4 thin films were prepared by thermal evaporation under vacuum (10?3?Pa). X-ray diffraction analysis of the deposited films revealed that, the as-deposited films were amorphous in nature and an amorphous-to-crystalline phase transition with a preferred orientation along (112) could be obtained by thermal annealing of the as-deposited films at 425?K for 0.5?h. The optical constants of the deposited films were determined in the spectral range 450?2500?nm. A graphical representation of log(?) versus log(1/?) shows two distinct, linear parts confirming the existence of both direct and indirect optical transitions. The corresponding band gap values were determined. The refractive index dispersion in the transmission and low absorption region is adequately described by the single oscillator model, whereby the values of the oscillator strength, So, oscillator position, ?o, dispersion parameter Eo/So and the high-frequency dielectric constant, ?? were calculated. The effective number of valence electrons per atom, n0,eff and the static dielectric constant, ?0,eff are deduced via the use of sum rules and are used to interpret the obtained optical data.

The pressure dependences of the lattice parameters, electronic structure, and bonding properties of the layered ternary compound Ti3SiC2 were investigated by performing ab initio plane-wave pseudopotential total energy calculations. The material exhibited elastic anisotropy. The lattice constants and axial ratio were studied for different pressures, and the same trend was obtained as is measured in experiment. It was found that although the structure was stable at high pressure, the electronic structure and atomic bonding were definitely affected. The electrical conductivity was predicted to reduce with pressure, which was interpreted by analysing the band dispersion curve and density of states at the Fermi level. The strengths of the atomic bonds in Ti3SiC2 were considered by analysing the Mulliken population and by examining the bond length contraction for various pressures. A redistribution of charge density that accompanied high pressures was also revealed.

The emission of episide down bonded InAsSbP/In(Ga)As/n+-InAs and graded InAsSb(P) light-emitting diodes (LEDs) with λmax = 3.3–5.5 μm has been modified with an 'internal' Fabry–Perot cavity or bandpass filter attached to the LED with an optical glue. Positive and negative emission with the full width at half-maximum close to that of the filter (8–20 meV) have been obtained in the 20–50 °C temperature range.

CuInSe2 (CIS) quantum dots (QDs) have been prepared by radio-frequency reactive magnetron sputtering from a ternary compound target on glass substrates coated with indium tin oxide at low temperatures. Uniformly distributed CIS QDs with a regular shape can be grown in this way. The average lateral size of the dots can be varied between 40 and 80 nm by making appropriate choices of substrate temperature, power density, and total CIS coverage.

CuInSe2 (CIS) nanoparticle thin films have been prepared by radio frequency reactive magnetron sputtering from compound ternary fan-shaped targets on low-temperature substrates with pure argon gas as the atmosphere. The stoichiometry of the ternary compound semiconductor quantum dots can easily be controlled by the ratios of the ternary elements and sputtering parameters. CIS nanoparticle thin films regularly shaped and distributed reasonably uniform in size on substrates of 7059 glass etc can be grown in this way. The average particle diameter can be varied between 40-80 nm by an appropriate choice of the substrate temperature, power density and total CIS coverage. The optical and electrical properties of the CIS films have also been studied.

Minority carrier injection annealing under forward-bias conditions is shown to enhance defect annealing in InGaP and to result in the recovery of solar cells properties. Such peculiar recovery of properties affected by radiation damage demonstrates that InGaP-based devices, under minority-carrier injection-mode operation, have superior radiation resistance compared to GaAs and Si. The first example of a recombination-enhanced mechanism in the ternary compound InGaP is also reported. We have performed detailed studies of the stability of the radiation-induced defect H2 in p-InGaP under various biases in order to determine the dependence of the reaction rate on the position of the Fermi level in the absence of minority carrier injection and recombination. Recombination-enhanced defect annealing of H2 causes a reduction of the minority carrier injection annealing activation energy, compared to thermal annealing from 1.69 eV to 0.52 eV. Analysis of the results reveals that the mechanism involved in the minority carrier injection annealing of the defect is the energy release mechanism, in which enhancement is induced by the energy that is released when a minority carrier is trapped at the defect site.

Transition metal chalcogenides have shown great potential for the applications in high performance optoelectronic devices. Here, we demonstrate for the first time the growth of V0.75W0.25Se2 van der Waals ternary alloy and its application in high performance photodetection. The crystals of V0.75W0.25Se2 were grown by direct vapour transport technique and chemical composition was confirmed by EDAX. The powder XRD results reveal the good crystallinity of grown samples, exhibits hexagonal lattice structure with P63/mmc space group. The XRD pattern also reveals the presence of 1T–VSe2 secondary phase. The SEM and TEM analysis are also carried out for structural analysis. The optical response, studied by photoluminescence spectroscopy discloses the various excitonic mechanisms of V0.75W0.25Se2 ternary alloy. The results of Raman spectroscopy discloses the presence of A 1g and E 2g modes of vibration and confirms the 2H-poly-type of grown V0.75W0.25Se2 ternary compound. The moderately fast time-resolved photoresponse is demonstrated under 670 nm laser light of power intensity 3 mW cm−2 at 0.3 V bias voltage. The quantitative analysis of performance was carried out from the determined detector parameters such as response time, photo-responsivity, external quantum efficiency and detectivity.

The results of the magnetic, electron transport, heat capacity and heat conduction measurements on the new rhombohedral ternary compound Pr2Rh3Ge have been investigated. The synthesized polycrystalline compound was found to crystallize in the ternary ordered variant of the cubic Laves phase [Formula: see text]-type of structure with the space group R[Formula: see text]m, as previously reported. Pr2Rh3Ge exhibits a ferromagnetic behaviour below [Formula: see text] K, which was found to be unstable in low applied magnetic fields, revealing characteristics usually attributed to the long-range order. In the entire paramagnetic region electrical resistivity shows monotonous metallic conductivity character. We estimated that the Sommerfeld coefficient γ = 315 mJ/Pr-mol · [Formula: see text] of [Formula: see text] [Formula: see text]Ge is very large with comparison to ordinary metals which indicate the existence of heavy fermion behaviour of itinerant charge carriers at low temperatures or enhanced density of the quasi-particle state at the Fermi level. The crucial role of the crystalline electric field effects on the ground state properties of [Formula: see text] (J = 4) has been also observed. We think that the heavy fermion behaviour in [Formula: see text] [Formula: see text]Ge results from the dynamic low-lying crystal-field fluctuations, since there is no sign of Kondo effect in electrical resistivity and no enhancement of the slope S(T)/T in thermoelectric power data at low temperatures. It suggests that the conduction electrons at the Fermi level does not correlate with the 4f 2 states of [Formula: see text] atoms and hence there is no place for a typical spin Kondo effect, as it is commonly observed in Ce- and Yb-based heavy fermion systems.

The composition, crystal structure and phase relationship of the main intermetallics of the Mg-Zn-La system on the low La side have been studied. The results show that there exists a binary solid solutions of Mg12La as (Mg,Zn)La12 and a linear ternary compound (Mg,Zn)11.5La. Though the composition formula of the two phases are similar, but the composition of Zn in them are different. The maximum Zn content of (Mg,Zn)12La is 7.2at% and the minimum Zn content of (Mg,Zn)11.5La is 8.5at%. What's more, the crystal structures of (Mg,Zn)12La and (Mg,Zn)11.5La phase are also totally different. (Mg,Zn)La12 have the body centered tetragonal lattice structure, but the crystal structure of (Mg,Zn)11.5La is C-centered orthorhombic lattice structure.

Different types of microcavities for GaAs-based light emitting devices operating in the 1.3 µm spectral range are analysed. Microcavity light-emitting diodes (MC LEDs) can be fabricated with different designs of distributed Bragg reflectors (DBRs), e.g.: top and bottom AlAs/GaAs semiconductor DBRs; bottom AlAs/GaAs semiconductor and top dielectric DBRs; and oxidized AlxOy/GaAs DBRs. MC LEDs operating in the 1.3 µm spectral range and characterized by spectral width (13 nm) and narrow far-field pattern ( 40%) differential efficiency retained. A threshold current of

The crystal field of the pseudo-ternary compound ErAlxGa2-x has been determined by means of inelastic neutron scattering for x = 0.5, 1.0 and 1.75. The thermodynamic properties reconstructed from the obtained crystal-field parameters are compared to neutron diffraction, specific heat and magnetic susceptibility measurements. The effect of increasing the Ga concentration on the crystal-field potential with respect to the change in geometry and the electronic properties of the solid is discussed by means of an extended point-charge model. It is concluded that Ga leads to an increase of the electron concentration and thus most likely triggers the structural phase transitions in the RAlxGa2-x systems (R = rare earth) by a Hume-Rothery-like electronic mechanism. The experimentally observed large broadening of the crystal-field transitions is discussed within the framework of concentration inhomogeneities.

Selectively n-doped AlxGa1-xAs/GaAs heterostructures with an additional p-type doped GaAs compensation layer on top were prepared by solid-source molecular beam epitaxy. If properly designed, these layer-compensated heterostructures are not conducting with the compensation layer present, whereas a two-dimensional electron gas (2DEG) is formed at the heterointerface if the compensation layer is removed. This makes the material well suited as a base material for nanolithography because lateral patterning of the compensation layer results in a laterally structured 2DEG. We found by simulation as well as experimentally that the n-type delta doping concentration is very critical and has to be correct within ±15% to obtain properly compensated heterostructures. For the non-compensated case, i.e. with the compensation layer removed, electron densities up to 4.3×1011 cm-2 before illumination and 9×1011 cm-2 after illumination have been achieved in structures that are insulating with a compensation layer. The obtained electron mobilities in the 2DEG are high, reaching a maximum value of 1.1×106 cm2 V-1 s-1 at 4.2 K after illumination.

In this paper we compare the characteristics of InP-based double-heterojunction bipolar transistors (DHBTs) with different emitter layer designs. The offset and saturation voltages can be significantly reduced by inserting an InP layer between a large-bandgap InAlAs emitter and a small-bandgap InGaAs base layer. The current gains of the composite-emitter (InAlAs/InP) DHBTs are higher than those of conventional InAlAs and InP DHBTs, especially at low currents. However, if the InP layer is too thick, the current gain decreases, presumably due to the suppression of quasi-ballistic transport.

We report on the microwave noise measurements in InP/InGaAs and GaAs/AlGaAs heterojunction bipolar transistors. Noise parameters Fmin , RN and Gopt were measured and simulated in a broadband frequency range (2-26 GHz). Small-signal equivalent circuit and noise model parameters for different biases were extracted.

Electrical properties of lattice-mismatch-induced defects in GaAs/GaAsSb and GaAs/InGaAs heterojunctions have been studied by means of an electron-beam-induced current (EBIC) in a scanning electron microscope and deep-level transient spectroscopy (DLTS). DLTS measurements, carried out with p-n junctions formed at the interfaces, revealed one electron trap and two hole traps induced by the lattice mismatch. The electron trap, at about Ec-0.68 eV, has been attributed to electron states associated with threading dislocations in the ternary compound. By comparing the concentration of this trap, revealed by DLTS, with EBIC results on the diffusion length, obtained for heterojunctions with different lattice mismatches, it is inferred that the minority-carrier lifetime is controlled by dislocations in the epilayer region close to the interface. Two new hole traps have been ascribed to defects associated with the lattice-mismatched interface of the heterostructures.

We report in situ etching in III-V molecular beam epitaxy (MBE) with AsBr3 as the etching species and MBE regrowth of in situ structured GaAs substrates. The application of AsBr3 provides atomic layer precise etching as well as full compatibility with MBE growth. The quality of etched interfaces in GaAs/AlGaAs heterostructures is investigated by photoluminescence (PL) and Hall-effect measurements. They indicate a slightly enhanced interface roughness for etched samples compared to as-grown structures but no incorporation of bromine could be detected. However, an insufficient removal of dopants as well as carbon and oxygen surface contamination was observed in SIMS studies. A material selectivity between the metallic components In, Ga and Al was investigated as well as a crystallographic selectivity in GaAs. Selective etching of SiO2 masked GaAs(100) substrates allows in situ preparation of extremely sharp V-grooves with almost perfectly planar {110} side facets. By MBE regrowth of V-grooves we prepared buried layers and completely embedded wires which were characterized by SEM and PL.

This report describes the epitaxial growth and fabrication of room-temperature InAs0.89Sb0.11/InAs0.48Sb0.22P0.30 semiconductor light emitting diodes operating in the mid-infrared wavelength region near 4.5 µm. The InAs0.89Sb0.11 ternary material used in the light emitting diode active region has a large lattice mismatch with respect to the InAs substrate layer and in order to accommodate this it was necessary to grow a buffer layer with an intermediate composition (InAs0.94Sb0.06). The devices exhibit infrared emission at 4.5 µm and could be effectively used as the basis of an optical sensor for the environmental monitoring of carbon monoxide at 4.6 µm and carbon dioxide at 4.2 µm in various applications.

Previously we developed a model for InAs/AlSb/GaSb resonant tunnelling structures (RTSs) and investigated the mechanisms of peak and valley current in these diodes, which exhibit high values of peak-to-valley (P/V) current ratio. Good quantitative agreement with the experiment was achieved both for the values of peak and valley current density for the first time. Here we show that the P/V current ratio can be essentially enlarged by employing the AlGaSb material instead of AlSb. The calculated current-voltage (I-V) characteristic of the InAs/AlGaSb/GaSb RTSs with 30 and 20 A barriers and 65 A quantum well showed a P/V current ratio of about 800 at lattice temperature T = 77 K. This value is much greater than all known experimental values of P/V current ratio for RTSs until now.

Strain relaxation and epitaxial layer tilt has been investigated for III-V based tandem solar cells grown on miscut Ge substrates. AlGaAs/InGaP/GaAs layers were grown by metalorganic vapour phase epitaxy on substrates miscut by 9° along a low crystallographic symmetry direction. We observe the GaAs buffer layer grown on the substrate to be 86% relaxed. The GaAs layer is tilted by 60 arcsec from the substrate, as determined by triple axis x-ray diffraction. This tilt stems from the miscut, the polar/non-polar interface and from the miscut direction lying away from a high symmetry direction. The observed magnitude of the tilt is not predicted well by existing models. Subsequently grown Al0.8Ga0.2As and In0.5Ga0.5P device layers are pseudomorphic with respect to the GaAs buffer layer, and exhibit the expected layer tilting of 58 and 125 arcsec respectively with respect to the Ge substrate. There is no rotation of the epitaxial layers with respect to the GaAs buffer layer.

We show that a vacancy-controlled model can explain the experimentally observed negative dependence on the stress temperature of GaAs/AlGaAs heterojunction bipolar transistors' degradation by non-radiative defects. The driving force (osmotic force) of the degradation versus the bias stress temperature is calculated and a decreasing temperature dependence is found. This model, which has previously been applied to strained-layer lasers and light emitting diodes, will help us understand the reported experimental observations on the temperature-acceleration tests for the GaAs/AlGaAs-based heterostructure devices such as heterojunction bipolar transistors.

We have investigated the ternary compound superconductors (NEG), (SEG) and (NSG) melt-processed in a reduced oxygen atmosphere with magnetic and magneto-optical measurements. Zero-field-cooled and field-cooled measurements were carried out in order to correlate the flux distributions with microstructure analysis. It was found that the critical state is well established in all three samples. The curves derived from magnetization loops exhibit a strongly developed secondary peak effect. Scaling of normalized as a function of reduced field, , was performed. At 77 K and above, it was found that NSG and SEG samples have similar properties, which are different from those of the NEG sample. The current-carrying length scale was determined from the reverse leg of the magnetization hysteresis loops and was compared with the actual dimensions of the sample.

A comparison of GaInP/GaAs HBTs with and without a base epitaxial regrowth is undertaken via static and low-frequency noise measurements. Current gain values and behaviour versus emitter area are different in both types of transistor. From low-frequency noise measurements emitter series resistances are extracted. Values of resistances are much smaller by about a factor of ten on samples without regrowth. The and g-r noise components are then analysed versus bias and geometry. For samples without regrowth, the and the g-r noise sources are mostly located at the extrinsic base surface and are due to recombinations. These recombinations are suppressed on samples with a base regrowth. On these devices, the noise sources related both to intrinsic and extrinsic phenomena are present. The g-r noise sources are located within the intrinsic transistor and more particularly in the base-collector space-charge region. This is partly explained by a thermal treatment induced by the process technology. Finally, it is shown that the base epitaxial regrowth brings a correlation between base and collector currents.

Two switching devices with different double carrier confinement structures were fabricated. One is a GaAs switch with double InGaP barriers, another with double GaAs-InGaAs delta-doped (-doped) quantum wells. In the characteristics of the former, because of the two-step barrier lowering induced by the processes of the carrier charging to the injection junction and carrier confinement in wells, a double S-shaped negative differential resistance (NDR) phenomenon is observed after the onsets of successive avalanche multiplications. However, only a single NDR performance is obtained in the characteristics of the latter due to one-step barrier lowering, even though successive avalanche multiplications also occur in the device operation.

The lateral coupling of waveguiding structures in both [011] and [011] directions is studied using embedded selective area epitaxy by chemical beam epitaxy. All growth steps are carried out under the same growth conditions on (100) InP substrates misoriented by 0.5 towards (111)B. Both planar and selectively grown material exhibits bright luminescence and narrow PL linewidths (8 meV FWHM at 4 K), up to the lateral junction. Moreover, no degradation of the original material properties is observed after regrowth. SEM images show very flat layers and excellent lateral coupling for all four types of junctions. After reactive ion etching of waveguide ridges, the optical coupling losses have been determined using a Fabry-Perot setup at 1530 nm (TE polarization). Values of 0.1 dB/interface with excellent uniformity are presented. From our results we conclude that, by optimization of the sample preparation prior to regrowth, values of 0.1 dB/interface can be obtained reproducibly for both perpendicular coupling directions.

The molecular beam epitaxy growth of strained (Ga, In)Sb/GaSb quantum wells is investigated. In a narrow range of growth conditions, (Ga, In)Sb quantum well structures exhibiting excellent structural properties as well as intense and narrow photoluminescence transitions are obtained. Stimulated emission at 1.98 m is observed at room temperature from laser diodes with strained quantum wells as the active zone. The lasers exhibit threshold current densities as low as 280 A and a characteristic temperature of 75 K.

AlGaAs/InGaAs quantum doped-channel field-effect transistors with a mesa gate and an airbridge gate were fabricated and compared. An additional processing technique was employed in fabricating the required airbridge with multiple piers. Experimental results reveal that the airbridge technology does not degrade device yield even if the materials were not selectively removed. Both dc and rf performance are enhanced when the airbridge technique is used in device fabrication. We obtained maximum extrinsic transconductance, available current density and breakdown voltage to be , and 8.5 V for a airbridge-gate device. A mesa-type device exhibits smaller values than the airbridge-gate one. Furthermore, the measured unit-current-gain frequencies were 19 and 14 GHz for airbridge- and mesa-gate devices, respectively.

We present microwave noise measurements performed on different high electron mobility transistor channels under both darkness and illumination. Two structures of /GaAs layers have been grown with beams of and using molecular beam epitaxy. The measured room temperature, Hall mobilities and sheet carrier densities have demonstrated in both cases a good dc performance of the channels. However, the measurement of the noise temperature at 1.5 GHz has shown the sample grown with to be considerably noisier than the one grown with .