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We present a comparison of different surface preparation techniques for hot-extruded (BiSb)(TeSe) alloys prior to Ni plating and their consequences on adhesion. The surface preparation is carried out by a relatively fast and well-controlled electrochemical etching procedure that provides morphologies with homogeneous flat surfaces on a scale of tens of micrometers. This procedure is not optimal for Ni metallization since it does not ensure enough roughness on the surface. Applying wet chemical etching with hypochlorite and nitric acid after the electrochemical etching changes the morphology, and the surface roughness increases, as evidenced by scanning electron microscopy and atomic force microscopy. Tensile tests carried out on n-type and p-type 1-mm-thick specimens, covered with a 12- μm Ni layer followed by Sn-Pb soldered joints, confirm a significant improvement in the ultimate adhesion strength, with fracture occurring within the thermoelectric material. Use of this two-step surface treatment, after slicing and prior to metallization, leads to maximum adhesion strength of around 38 MPa for either type of thermoelectric material. These results are consistent with the morphological changes observed by scanning electron microscopy on the surface after chemical etching. [ABSTRACT FROM AUTHOR]

We report on the annealing of InP and GaAs substrates, placed side by side, in a hydrogen atmosphere. This annealing is done with and without arsine, and also in the presence of elemental arsenic replacing GaAs. This simple technique shows the stabilization of InP by the presence of GaAs in a temperature range between 550 and 750 °C. It gives information about active species present during substrate annealing. The results obtained show that the protecting species of column V elements, dimers or tetramers, behave differently than the ones resulting from the decomposition of the V hydride. [ABSTRACT FROM AUTHOR]

Photovoltaic spectra of InGaAs/GaAs multiple quantum wells grown by metalorganic vapor phase epitaxy show several well defined spectral structures which are interpreted in terms of the sample characteristics. Results obtained by this relatively simple method are comparable to data obtained by other optical techniques on the same material, and in good agreement with calculations taking into account the strain-induced splitting and the coupling between the wells. [ABSTRACT FROM AUTHOR]

Strained-layer superlattices (SLS’s) of GaxIn1-xAs/GaAs (x[bar_over_tilde:_approx._equal_to]0.8–0.9) have been grown by low pressure metalorganic vapor phase epitaxy. The reactants were trimethylgallium, trimethylindium, and arsine. The structures were characterized by Auger profiling and low-temperature photoluminescence. These measurements show that high quality SLS’s with interface widths no larger than 25 Å and very narrow luminescence peaks (6.5 meV) similar to the best structures grown by molecular beam epitaxy, can be easily grown by low pressure metalorganic vapor phase epitaxy. [ABSTRACT FROM AUTHOR]

The effects of biaxial in-plane stress on the elastic, dielectric, and piezoelectric (PE) properties of c-axis textured thin film wurtzite phase scandium aluminum nitride (w-ScxAl1−xN) alloys have been calculated with density functional perturbation theory. The in-plane stress σR was kept below 1 GPa covering compressive and tensile values and applied to alloy supercells represented with special quasi-random structures. An increasingly tensile biaxial stress (σR > 0) produces higher displacement-response internal-strain coefficients for the constituent atoms of the alloy and the related PE properties are more sensitive to σR when the fraction x increases. A significant rise of the relative dielectric permittivity ϵ r , 33 η and softening of the stiffness coefficient c 33 E are also reported with σR > 0. The effective thin film PE strain coefficient d33,f and coupling coefficient k 33 , f 2 show a relative increase of 22% and 26%, respectively, at σR = 1 GPa and x = 0.438. Both tensile σR and x tend to decrease the c/a cell parameter ratio of the wurtzite structure with a significant impact on the PE coefficients. Based on the decomposition of the stiffness, dielectric, and PE coefficients as well as the structural data, it is suggested that tensile biaxial stress enhances the hexagonal character of w-ScxAl1−xN in a qualitatively similar manner as the scandium nitride fraction x does. The manufacture and PE characterization of a beneficially stressed thin film of w-ScxAl1−xN on a substrate of w-InyAl1−yN with adjusted x, y values are suggested to confirm the calculated values of d33,f. [ABSTRACT FROM AUTHOR]

MnP nanostructures embedded in GaP epilayers, and MnP polycrystalline films, grown from the vapor phase on GaP(001) substrates using metalorganic precursors are compared with bulk MnP. We observe a large increase of the low transition temperature from the ferromagnetic to the antiferromagnetic screw phase, from TN = 47 K for bulk to 82 K for nanocrystals in MnP:GaP films, while the Curie temperature TC, close to room temperature, varies only slightly. A net magnetic moment is measured in the nanocrystals and films at 5 K, as well as large coercive fields, contrary to bulk MnP. X-ray absorption spectroscopy and diffraction show that epilayers and films contain MnP grains in the nanometric range with average Mn-P bond lengths very close to those of bulk MnP. The MnP film lattice parameters are almost identical to bulk values (within 0.5%) and the main crystallographic preferential orientations are those also present in the epilayers but with different relative populations. Overall the local structures of all MnP forms are very similar, except for indications of more disorder in the nanocrystals. Such combined changes of TN and TC are in apparent contradiction with the known response of bulk MnP to strains induced by hydrostatic, uniaxial or chemical pressure. We conclude that the differences in the low temperature magnetic behavior are most probably originated by local structural disorder at the surface of the nanostructures and by finite size effects. [ABSTRACT FROM AUTHOR]

Hybrid ferromagnetic-semiconductor GaP:MnP thin films were grown at 650 °C by metal-organic vapor phase epitaxy on GaP(001) using trimethylgallium, tertiarybutylphosphine, and methyl cyclopentadienyl manganese tricarbonyl (MCTMn). Overall Mn concentrations in the hybrid films, determined by Rutherford backscattering spectrometry, were found to be nearly proportional to the MCTMn precursor gas flow rate and ranged from 2 to 3.5 at. %. Cross-sectional transmission electron microscopy (TEM) analyses revealed the presence of a homogeneous distribution of 15–30 nm wide nanoclusters in a dislocation-free GaP matrix that is fully coherent with the substrate. The nanocluster facets are predominantly aligned along the (220) planes of the GaP matrix and selected-area electron diffraction patterns in TEM indicate that the nanoclusters are coherent (or semicoherent) with the single-crystal GaP matrix. The Mn:P composition ratio in the nanoclusters was determined to be 1.00±0.05 from parallel electron energy loss spectroscopy analyses. Increasing the MCTMn flow rate during film growth resulted in an increased concentration of MnP nanoclusters in the epilayer while their dimensions remained virtually unchanged. Magnetometric characterization indicates a ferromagnetic order, with a Curie temperature of about 294 K, originating from the MnP clusters. [ABSTRACT FROM AUTHOR]

We have investigated the optical emission from GaAs1-xNx epilayers with 4.3×10-4

A tetrahedral model is presented to explain the bonding properties of nonstoichiometric amorphous silicon oxynitride (a-SiOxNy) alloys, grown under highly nonequilibrium conditions, whose structures obey neither the random bonding model nor the random mixture model. Based on our approach, a numerical procedure is proposed to obtain the relative atomic percentages of each component structural phase from the deconvolution of the high-resolution x-ray photoelectron spectroscopy (XPS) spectra in the Si 2p3/2 region. The tetrahedral model is then used to study the bonding properties of a-SiOxNy films grown by electron-cyclotron resonance plasma-enhanced chemical-vapor deposition, having relatively low values of the O/Si atomic ratio (<=0.37) incorporated in their networks. The experimental results show that five tetrahedral phases (tetrahedrons Si–Si4, Si–Si2ON, Si–N4, Si–Si3O, and Si–O4) are present in a-SiOxNy films with low N/Si atomic ratios (<=0.93), while only three phases (Si–SiON2, Si–N4, and Si–O2N2) are present in samples with higher N/Si atomic ratios (>=1.12). The Si3N4 phase is the most important bonding unit and it is the only phase present in all our samples. These results are corroborated by survey scans and by comparison with the high-resolution XPS spectra in the N 1s region. They support the validity of the model proposed for a-SiOxNy alloys and the XPS analysis, correlated with growth conditions, presented in this work. [ABSTRACT FROM AUTHOR]

A concept for the implementation of a compliant substrate using a buried layer of nanocavities is presented. The purpose of this nanocavity layer is to mechanically decouple a thin substrate layer from the rest of the substrate in order to relax stress in mismatched epilayers. The nanocavities were created by helium implantation in InP(001) followed by thermal annealing under a phosphorous rich atmosphere. Metalorganic vapor phase epitaxy of InAsP/InP heterostructures grown simultaneously on substrates with nanocavities and on conventional substrates were characterized by high-resolution x-ray diffraction, transmission electron microscopy, and optical absorption. It is found that strain relaxation is enhanced for heterostructures grown on substrates with nanocavities and that the dislocations propagate partly in the compliant layer instead of the epilayer. The critical thickness of heterostructures grown on conventional substrates is roughly double that of structures grown on substrates containing nanocavities. [ABSTRACT FROM AUTHOR]

We present the electrical transport properties of thermoelectric n-type Bi[sub 2](Te[sub 1-χ] Se[sub χ])[sub 3] (χ ≤ 0.125) polycrystalline alloys obtained by mechanical alloying and extrusion. It was determined that the charge carrier mobility decreases in the temperature range 90-300 K as the content (χ) of Bi[sub 2]Se[sub 3] is increased. The observed decrease is larger than what could be predicted by the introduction of an alloy scattering mechanism due to the electronegativity difference between Se and Te atoms. It can be explained by the introduction of additional defects induced by the Se incorporation, whose concentration is reduced by thermal annealing following extrusion. In the extrinsic regime, the observed temperature dependence of the mobility [µ = µ[sub 0](T/T[sub 0])[sup r]] of as extruded alloys apparently indicates that charge carrier scattering is mostly limited by acoustic phonons (temperature coefficient r near -1.5). Annealing after extrusion changes the temperature coefficient to values near -1.7 which is closer to what has been reported for pure crystalline Bi[sub 2]Te[sub 3]. [ABSTRACT FROM AUTHOR]

Fully-coherent Si[sub 0.7]Ge[sub 0.3] layers were deposited on Si(001) by gas-source molecular beam epitaxy (GS-MBE) from Ge[sub 2]H[sub 6]/Si[sub 2]H[sub 6] mixtures in order to probe the effect of steady-state hydrogen coverages θ[sub H] on surface morphological evolution during the growth of compressively strained films. The layers are grown as a function of thickness t at temperatures, T[sub s]=450–550 °C, for which strain-induced roughening is observed during solid-source MBE (SS-MBE) and deposition from hyperthermal beams. With GS-MBE, we obtain three-dimensional (3D) strain-induced growth mounds in samples deposited at T[sub s]=550 °C for which θ[sub H] is small, 0.11 monolayer (ML). However, mound formation is dramatically suppressed at 500 °C (θ[sub H]=0.26 ML) and completely eliminated at 450 °C (θ[sub H]=0.52 ML). We attribute these large differences in surface morphological evolution primarily to θ[sub H](T[sub s])-induced effects on film growth rates R, adatom diffusion rates D[sub s], and ascending step-crossing probabilities. GS-MBE Si[sub 0.7]Ge[sub 0.3](001) growth at 450 °C remains two dimensional, with a surface width <0.15 nm, at all film thicknesses t=11–80 nm, since both R and the rate of mass transport across ascending steps are low. Raising T[sub s] to 500 °C increases R faster than D[sub s] leading to shorter mean surface diffusion lengths and the formation of extremely shallow, rounded growth mounds for which remains essentially constant at =0.2 nm while the in-plane coherence length increases from =70 nm at t=14 nm to 162 nm with t=75 nm. The low ascending step crossing probability at 500 °C results in mounds that spread laterally, rather than vertically, due to preferential attachment at the mound edges. At T[sub s]=550 °C, the ascending step crossing probability increases due to both higher thermal activation and lower hydrogen coverages. ... [ABSTRACT FROM AUTHOR]

Presents information pertaining to the quantum-confined Stark effect (QCSE) which relates to the band alignment engineering. What the term QCSE refers to; Capacity of the low valence band barriers; Detailed information on the QCSE.

Strained-layer multiple quantum well (MQW) InAsP/InP optical modulators have been fabricated from layers grown by metal-organic vapor phase epitaxy. The devices are a series of p-i(MQW)-n photodiodes in which the active core regions consist nominally of 25 periods of 10 nm InAsP quantum wells of 4.4%, 10.0%, 15.6%, and 26.4% As composition separated by 10 nm InP barriers. Structural parameters for the samples were obtained using high-resolution x-ray diffraction rocking curves and transmission electron microscopy. The series contains samples with both coherently strained and partially relaxed multi-layers where the relaxation is characterized by misfit dislocations. The band offsets for the heterostructures were determined by fitting the energy positions of the optical absorption peaks with those computed using the Marzin-Bastard model for strained-layer superlattices [as in M. Beaudoin etal., Phys. Rev. B 53, 1990 (1996)]. The conduction band discontinuities thus obtained are linear in the As composition (7.56 ± 0.08 meV per As % in the InAsP layer) at low and room temperature for As concentrations up to 39%, and up to 17% average relaxation. Comparisons between the coherently strained and partially relaxed samples demonstrated a broadening of optical transition linewidths due to relaxation which appears to be of minor consequence for optical modulator devices as the essential optical and electrical properties remain intact. The electric field-dependent red-shift of the n = 1 electron-heavy hole transition was measured by a photocurrent method and found to be enhanced in structures with lower barrier heights. [ABSTRACT FROM AUTHOR]

Deals with a study which assessed heteroepitaxial InP layers on silicon metalorganic vapor phase epitaxy using thermal cycle growth. Experimental details; Results; Discussion and conclusions.

Part I. Deals with the analysis of the strain-relaxation mechanisms in tensile-strained Ga[subx]In[sub1-x]P/indium phosphide heterojunctions by transmission electron microscopy. Experimental details; Nature and distribution of structural defects in the samples; Conclusion.

Presents a study which determined the structural and optical properties of strain-relaxed InAsP/indium phosphide heterostructures grown by metalorganic vapor phase epitaxy on indium phosphide(100) using tertiarybutylarsine. Experimental methods; Experimental results; Conclusion.

Deals with a study which determined the origin of the spatial luminescence fluctuations observed between the dark line defects present in tensile strained Ga[subx]In[1-x]P/In/n-InP heterostructures. Experimental details; Beam energy experiments; Conclusion.