Some features of the electrophysical properties of p-Ge layers produced on nonorienting substrates

The technology of producing single-crystal layers of Ge on nonorienting substrates is described. The distribution of the electrophysical properties across the surface and through the thickness of the layers at temperatures of 77 and 300°K are reported. It is shown that up to a thickness of d 2 the layers have uniformly distributed properties.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 26–31, May, 1973.     

Spinodal-like decomposition of InGaP epitaxial layers grown on GaP substrates

The spinodal-like decomposition of In_xGa_1−xP epitaxial layer prepared by low-pressure metallorganic vapour phase epitaxy was studied by means of photoluminescence and transmission electron microscopy. Epitaxial layers were grown on GaP substrates at T_g = 740 °C and reactor pressure of 20 mbar. We show that presence of spinodal-like decomposition occur at samples with InP mole fraction higher as x = 0.2 and V/III ratio of 75. The low-temperature photoluminescence spectra shows that in partially decomposed samples a characteristic broad band occurred close to 1.985 eV. An increase in the V/III ratio up to a value of 350 suppressed the decomposition, and PL signal with only one narrow transition was obtained.     

Nuclear magnetic resonance study of epitaxial Co layers on single-crystal substrates

Nuclear magnetic resonance (NMR) is a powerful tool to study the local structure of ultrathin magnetic films and multilayers. This is demonstrated with an NMR study of ultrathin molecular beam epitaxy-grown Co layers on single-crystal Cu(111), Cu(110) and Pd(111) substrates. Co on Cu(111) results in a mixture of fcc and hep phases and the Cu(111)/Co interface is near to perfect. Co on Cu(110) grows mainly fcc in long stripe-shaped islands with rough Co/Cu interfaces. Finally, Co on Pd(111) gives a (111)-oriented fcc structure. The top surface is flat, but the Pd(111)/Co surface is intermixed.     

Growth and properties of epitaxial iron oxide layers

Epitaxial layers of iron oxides have been grown on a MgO(001) substrate by evaporating natural Fe or⁵⁷Fe from Knudsen cells in the presence of a NO₂ flow directed to the substrate. The resulting layers have been investigated in situ with LEED, RHEED, AES and XPS and ex situ with CEMS and ion beam analysis. For substrate temperatures between 200 and 400°C we observe RHEED oscillations during deposition, indicative of layer-by-layer growth. By adjusting the flux of NO₂ at the surface, all stable and metastable cubic phases in the Fe-O system could be grown: FeO (wustite), Fe₃O₄ (magnetite), -Fe₂O₃ (maghemite) and solid solutions between the latter two phases. Rutherford backscattering spectra show a relatively high minimum yield in the channel directions.     

Grain boundary layers in nanocrystalline ferromagnetic zinc oxide

The complete solubility of an impurity in a polycrystal increases with decreasing grain size, because the impurity dissolves not only in the crystallite bulk but also on the grain boundaries. This effect is especially strong when the adsorption layers (or the grain boundary phases) are multilayer. For example, the Mn solubility in the nanocrystalline films (where the size of grains is ∼20 nm) is more than three times greater than that in the ZnO single crystals. The thin nanocrystalline Mn-doped ZnO films in the Mn concentration range 0.1–47 at % have been obtained from organic precursors (butanoates) by the “liquid ceramic” method. They have ferromagnetic properties, because the specific area of the grain boundaries in them is greater than the critical value [B.B. Straumal et al., Phys. Rev. B 79, 205206 (2009)]. The high-resolution electron transmission microscopy studies show that the ZnO nanocrystalline grains with the wurtzite lattice are separated by amorphous layers whose thickness increases with the Mn concentration. The morphology of these layers differs greatly from the structure of the amorphous prewetting films on the grain boundaries in the ZnO:Bi₂O₃ system.     

Mismatch and electron mobility in MBE GaxIn1−xas epitaxial layers on InP substrates

Composition inhomogeneity in nearly matched epilayers of the ternary semiconductor alloy Ga_xIn_1–xAs (x close to 0.47), grown by molecular beam epitaxy (MBE) on (001) InP substrates is correlated to variation of the lattice mismatch by x-ray imaging and local diffractometry. Misfit dislocations are shown to develop in areas of large misfit (above 2 × 10^–3) and are at the origin of a severe degradation of the electron mobility: an increase by a factor of about 4 in the intrinsic misfit (2.3 × 10^–3 compared to 0.6 × 10^–3) results in a 35 % reduction of the 77 K electron mobility.Part of this work has been done while this author was with Thomson-CSF Central Research Laboratory, Orsay, France     

Laser excitation induced photoluminescence linewidth reduction in molecular beam epitaxial InAlAs layers grown on InP substrates

An experimental investigation is presented on the influence of laser excitation on the photoluminescence (PL) linewidth in InAlAs layers grown lattice matched to InP substrates by molecular beam epitaxy (MBE). Measurements performed on silicon-doped samples and samples grown at different arsenic overpressures (V/III flux ratio) showed that the linewidth decreases with increasing laser excitation power. A model describing an unbalanced migration of photo-generated charge carriers due to the presence of clusters is proposed to explain the effect of the linewidth reduction. Also, the trend of the linewidth decrease becomes more pronounced in InAlAs samples with higher silicon doping concentrations and those grown at higher V/III ratios. Samples with higher silicon-doping concentrations have broader linewidths which could be the result of poorer alloy quality due to the presence of disorder (S. F. Yoon et al., J. Appl. Phys. 78, 1812 (1995)). A similar trend of linewidth reduction was observed at temperatures as high as 30 K. Our results show that such a measurement of linewidth vs. laser excitation power can be used as a supplementary method for InAlAs material characterization.     

Surface-relief micropatterning of zinc oxide substrates by micromolding pulsed-laser-deposited films

Surface-relief patterning of semiconductor surfaces has become a very active research topic during the last few years. This growing interest is related to the wide range of technological applications of patterned semiconductor surfaces, with particular emphasis on photovoltaic technology. In this work, we show a straightforward, cost-effective and non-hard lithographic approach for transferring surface-relief micropatterns on ZnO surfaces. The method is based on direct micromolding of pulsed-laser deposited ZnO films using surface-modified metallic micromolds. In contrast to those obtained by photolithographic techniques, direct micromolded ZnO surfaces are characterized by very low roughness values on the transferred relief patterns. PACS 81.15Fg; 81.20Hy; 81.16Mk; 81.61Cf     

Infrared angular spectroscopy characterization of epitaxial layers of n-type silicon grown on N+ or P+ substrates

Summary In this paper the technique of infrared angular spectroscopy applied to the characterization of epitaxial layers ofn-type silicon grown on N⁺ or P⁺ substrates is illustrated. Some results are reported and discussed concerning films having a free-carrier concentration ranging from 10¹⁴ cm⁻³ to 10¹⁷ cm⁻³ and thickness of the order of 10 μm. A significant comparison with results obtained by other techniques (four-point probe, spreading resistance,C−V plots, etc.) is performed and a few simple conclusions are drawn. To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.     

Multi-stacked organic light-emitting diodes using zinc oxide nanoparticle interfacial layers

Stacked organic light-emitting diodes (SOLEDs) with 30-nm nanoparticle (NP) interfacial layers were investigated. Zinc oxide (ZnO) was used as an interfacial layer between two green polymer (GP) layers. SOLEDs with NP interfacial layers had higher device efficiency than did a single-unit device due to the high probability of exciton recombination that originated from the Auger electron-assisted energy up-conversion process. Although the current density and luminance of SOLEDs with ZnO NP interfacial layers were smaller than those of the reference device, the efficiency was doubled because of the big band alignment difference and the large band gap between GP and ZnO NP interfacial layers, which induced more radiative-exciton recombination.     

Structural defects in 6H-SiC substrates and their effect on the sublimation growth of epitaxial layers in vacuum

The structural perfection of silicon carbide substrates and homoepitaxial layers grown on the substrates by sublimation has been studied by x-ray diffraction (topography and diffractometry) and optical microscopy. The optimum diffraction conditions (hkil reflections, radiation wavelength λ, and recording geometry) for revealing “micropipes” of the dislocation nature are determined. It is shown that the growth conditions used make it possible to obtain highly perfect epitaxial layers.     

The epitaxial growth of ice on single-crystalline substrates

Epitaxial deposits of ice crystals have been formed on the basal (0001) faces of hexagonal AgI, PbI₂, CuS, CdI₂ and brucite, on the (001) face of freshly-cleaved muscovite, on the (010) face of orthorhombic HgI₂, on the (001) face of orthorhombic iodine, on the (100) face of V₂O₅and on the rhombohedral faces of calcite. The temperature at which ice crystals first appear on a particular substance is very close to the threshold temperatures at which an aerosol of the same substance nucleates a cloud of supercooled water droplets.The crystals appear preferentially at cleavage and growth steps on the substrate surface, provided that these exceed ~ 0.1μ in height and preserve their parallel orientation irrespective of the direction of the step.Thin, hexagonal ice plates, growing on the basal plane of covellite (CuS), show interference colours which give a measure of their thickness. Commonly, the ice crystals increase appreciably in diameter with no discernible change of thickness, suggesting that molecules arriving on the upper surface are not assimilated but migrate over the surface and are built in at the crystal edges. Crystals usually thicken on touching a neighbouring crystal; coloured growth fronts are then seen spreading out across the crystal surface from the point of contact.Detailed measurements on AgI, PbI₂, CuS and CdI₂ show that, for a given substance, there is a well-defined critical temperature above which ice crystals can appear only if the air exceeds saturation relative to liquid water, but below which ice forms directly from the vapour phase provided that the supersaturation relative to ice exceeds 12 per cent for silver iodide and slightly different values for the other substrates. These critical supersaturations are required for growth at the edges of steps; ice appears on the flat parts of the substrate only at much higher supersaturations (> 100 per cent).     

Photoconductive response of GaAs epitaxial layers

In the present work the photoconductive response of low resistivity, n-type GaAs epitaxial layers is studied by experimentally monitoring the dependence of the photoconductive gain (PG) optoelectronic parameter upon incident photon flux and temperature. The characterized samples fall into three major categories: ion implanted (II) GaAs epilayers formed within undoped, semi-insulating GaAs substrates; GaAs epitaxial layers grown by liquid phase epitaxy (LPE) on Cr-doped, semi-insulating GaAs substrates; and ungated GaAs MESFETs.     

Effect of precursor concentration on the growth of zinc oxide nanorod arrays on pre-treated substrates

Well aligned zinc oxide nanorod arrays (ZNAs) synthesized by a simple chemical bath deposition method were fabricated on pre-treated Si substrates. By keeping the molar VI/II ratio constant, the effect of precursor concentration on the growth and optical quality of the ZNAs was investigated. The as-synthesized ZNAs were characterized by field emission scanning electron microscopy (FESEM), x-ray diffraction (XRD) and photoluminescence spectroscopy (PL). FESEM images show that both the diameter and aspect ratio of the ZNAs increase dramatically as the precursor concentration increases. The XRD analysis indicates that all the as-grown ZNAs are crystalline and are preferentially oriented along the c-axis. The high intensity ratio of the UV emission to visible emission in the room temperature PL spectra illustrate that high optical quality ZNAs were produced.     

Hopping conduction in epitaxial n-GaAs layers

The conductivity results of the phonon-assisted hopping process in n-type GaAs at low temperatures are presented. The conductivity variation with T, N_D and H are analyzed in terms of the percolation theory results.     

HgCdTe外延薄膜临界厚度的理论分析

基于在任意坐标系内应力与应变的关系、晶体弹性理论和位错滑移理论，研究了生长方向分别为［111］和［211］晶向，HgCdTe外延薄膜临界厚度与CdZnTe衬底中Zn组分和HgCdTe外延层中Cd组分的关系. 结果表明，HgCdTe外延薄膜临界厚度依赖于CdZnTe衬底中Zn组分和HgCdTe外延层中Cd组分的变化. 对于厚度为10μm，生长方向为［111］晶向的液相外延HgCdTe薄膜，要确保HgCdTe/CdZnTe无界面失配位错的前提条件，是CdZnTe衬底中Zn组分和HgCdTe外延层中Cd组分的波动必须分别在±0.225‰和±5‰范围内；而对于相同厚度，生长方向为［211］晶向的分子束外延HgCdTe薄膜，CdZnTe衬底中Zn组分和HgCdTe外延层中Cd组分的波动范围分别为±0.2‰和±4‰. 关键词： HgCdTe/CdZnTe 临界厚度 位错滑移理论 失配位错     

Ohmic contacts to GaAs epitaxial layers

Formation of ohmic contacts onto GaAs epitaxial layers was reviewed. Because the Fermi energy of GaAs is pinned at the surface near the middle of the bandgap, it is impossible to choose a metal with the proper work function to make an ohmic contact. Instead, it is necessary to create a heavily doped surface layer and using field emission or thermionic field emission to achieve an ohmic contact. The oldest known contact metallization for GaAs is sequentially deposited thin films of Au, Ge, and Ni. It was shown that the ‘dopant diffusion model’, widely accepted to date to explain the formation of an n⁺ layer on GaAs to form the ohmic contact, is incorrect. Instead, the “solid phase regrowth model” was discussed in detail and shown to describe formation of ohmic contacts in this system. Based on this result, general rules for forming ohmic contacts to compound semiconductors with pinned Fermi levels or large values of electron affinities plus bandgap were expressed.