Temperature effect on the structure of ZnSe layers grown by chemical vapor deposition

The heat exchange between the substrate, growing layer, and gas flow in a CVD reactor is analyzed theoretically. The results indicate that the temperature of the gas mixture in the reactor influences the surface temperature of the polycrystalline zinc selenide deposit. Experimental data are presented on the variation of the average grain size across the ZnSe deposit. The thermal conditions of CVD and secondary crystallization during long-term deposition are shown to have a significant effect on the depth distribution of the grain size.     

Single-crystalline GaAs, AlGaAs, and InGaAs layers grown by metalorganic VPE on porous GaAs substrates

Conditions for the growth of single-crystalline GaAs, AlGaAs, and InGaAs layers by metalorganic VPE were established and the corresponding semiconductor films were obtained on porous GaAs substrates. Comparative data on the morphology, structure, and electrical homogeneity of the epitaxial layers grown on the porous and monolithic substrates are presented. It was found that passage to the porous substrates leads to changes in the film growth rate and morphology, the concentration of electrically active defects, and their distribution in depth of the epitaxial structures.     

Morphology and optical properties of GaAs layers grown on (1 1 1)A GaAs substrates in N2 ambient by metalorganic chemical vapor deposition

Using tertiary-butyl arsine as a group V precursor, GaAs epitaxial layers have been grown on both (1 1 1)A- and (1 0 0)-oriented GaAs substrates in N₂ ambient using the atmospheric metalorganic chemical deposition technique. The surface morphology and optical properties of the GaAs homoepitaxial layers were studied in detail. It is found that both the surface morphologies and optical properties of GaAs layers on (1 1 1)A GaAs substrates depend much more strongly on the combination of growth temperature and V/III input molar ratio, compared to the epitaxial layers on (1 0 0) plane GaAs. The photoluminescence (PL) emission efficiency increases with increasing growth temperature in the region 550–650 °C for both (1 1 1)A and (1 0 0) GaAs epitaxial layers. At room temperature, the PL emission intensity of the (1 1 1)A GaAs epilayer grown under optimum growth conditions is 67 times as strong as that of the same run-grown (1 0 0) GaAs epilayer.     

Cubic GaN layers grown by metalorganic chemical vapor deposition on GaN templates obtained by nitridation of GaAs

Cubic gallium nitride epitaxial layers were grown by metalorganic chemical vapor deposition on GaN templates obtained by nitridation of GaAs substrates. The GaN structure can be peeled off the GaAs substrate and it can be handled separately. X-ray diffraction, Raman and photoluminescence measurements show that the epitaxial layers are cubic and monocrystalline.     

Kinetics and edge-growth effects of GaAs LPE layers grown in the Ga-As-Bi system

Studies of the growth kinetics of GaAs epitaxial layers obtained from Ga-As and Ga-As-Bi solutions are compared in this work. We applied an equilibrium cooling method in a classic liquid phase epitaxy (LPE) system with the use of slider-type boats. The studies were carried out for Ga-As-Bi solutions containing 0 to 95% wt % Bi and also for Ga-As solutions at the same technological parameters of the growth process for comparison purposes. It is shown that in the applied range of bismuth concentration in the alloys, the GaAs growth rate is 0.5 to 3 times higher than for classic Ga-As solutions. It is found that the presence of bismuth in the solutions eliminates a disadvantageous GaAs edge-growth on the layer edges and considerably decreases the number of meniscus lines on the deposited layer surface.     

Effect of a ZnSe buffer layer on the surface, structural, and optical properties of the ZnTe/ZnSe/GaAs heterostructures

Lattice-mismatched ZnTe epilayers on GaAs (1 0 0) substrates with and without ZnSe buffer layers were grown by using molecular beam epitaxy. AFM, XRD, and TEM measurements were performed to investigate the surface and structural properties of the ZnTe thin films. Photoluminescence, Raman scattering, and TEM measurements showed that the crystallinity of a ZnTe epilayer grown on a GaAs substrate was remarkably improved by using a ZnSe buffer layer. Photoreflectance measurements showed that the strain of the ZnTe layer with the ZnSe buffer layer was smaller than that without the ZnSe buffer layer. These results indicate that ZnTe epitaxial films grown on GaAs substrates with ZnSe buffer layers hold promise for potential applications in optoelectronic devices operating in the blue-green spectral region.     

Structure and properties of ZnSe films grown by electrochemical deposition

ZnSe films with the sphalerite structure have been grown through electrochemical deposition from alkaline solutions. The films grown at a current density of 0.05 A/cm² consist of spherical grains ranging in size from 0.5 to 1 µm. The films are p-type and range in resistivity from 1.5 × 10⁶ to 6.8 × 10⁶ Ω m. Their band gap ranges from 2.37 to 2.55 eV.     

Effect of InAlGaAs and GaAs combination barrier thickness on the duration of dot formation in different layers of stacked InAs/GaAs quantum dot heterostructure grown by MBE

Multilayer stacks of quantum dots (QDs) (10 periods) with a combination barrier layer of In0.21Al0.21 Ga0.58As (30 angstroms) and GaAs (70-180 angstroms) are grown by solid source molecular beam epitaxy (MBE) and reflection high-energy electron diffraction (RHEED) has been used for the in situ determination of the duration of dot formation in the QD layers. The increase in the duration of dot formation in the consecutive layers of the QD heterostructure with thinner barrier is attributed to the indium migration towards the defects in the strained QD layers. A thicker GaAs layer at 590 degrees C overgrown on the InAlGaAs is believed to remove the unevenness of the growth front for the subsequent QD layer resulting in good vertical stacking of islands till the final layer of the multilayer heterostructures.     

Selective doping of conformal GaAs layers grown by hydride vapour phase epitaxy on Si substrates studied by spatially resolved optical techniques

High quality GaAs layers on silicon substrates were grown by conformal growth. In this technique, the GaAs conformal growth is initiated on the sidewalls of GaAs seed stripes (typically 10 μm wide with a pitch of 200 μm) grown conventionally on a Si substrate, and developed inside a cavity formed by the silicon substrate and an overhanging dielectric cap layer. The conformal layers were grown by hydride vapour phase epitaxy (HVPE) and doped with Si or Zn. The properties of these layers were studied by micro-Raman, cathodoluminescence (CL) and micro-photoluminescence (PL). The free carrier concentration was obtained with a micrometric spatial resolution. Both n-type (Si) and p-type (Zn) doping was achieved, showing the feasibility of selective doping and p–n homojunctions.     

Transmission electron microscopy structural characterisation of GaN layers grown on (0001) sapphire

GaN layers grown by MOCVD or by MBE on (0001) sapphire have been characterised by transmission electron microscopy (TEM). We make a review of the different crystallographic structures found in theses GaN layers. We comment shortly on the nitridation of the sapphire and the structure of the buffer layer (BL). We point out that the roughness of the BL can be an important parameter for releasing the residual strain of the GaN layer. We compute the Keating energies of the main inversion domain boundaries (IDBs) and translation domains boundaries (TDBs) observed in some GaN layers. The observed structures correspond to the lowest energy models. Perfect dislocations have Burgers vectors equal to a, a+c and c. The dislocation lines are generally parallel to the c-axis. a-Edge dislocations are generally not dissociated and we propose an atomic model for them. Screw dislocations with a Burgers vector equal to c, can ‘open and close' during growth leaving holes (the so-called nanopipes) in the structure.     

Morphology and rotation twin in ZnSe on GaAs (111)

ZnSe crystals were grown by a vapour transport method on a GaAs substrate with a (111) A or (¯1¯1¯1) B surface. Crystals obtained on the (111) A surface of the substrate were fine crystals and hexagonal plates. Whereas crystals grown on the (¯1¯1¯1) B were uniform thin films on which trigonal hills and trigonal pyramids developed. These crystallites had a complicated morphology. In addition, the hill and pyramid grown on the (¯1¯1¯1) B surface contained rotation twins around a polar axis parallel to the growth direction or around the other polar axes.     

Monocrystalline thin films of ZnSe and ZnO grown by atomic layer epitaxy

We report on the growth of monocrystalline thin films of ZnSe and ZnO by atomic layer epitaxy by simple reaction between elemental precursors. Structural and optical properties of these films are discussed with reference to the investigations performed with atomic force microscopy, scanning electron microscopy, cathodoluminescence and photoluminescence.     

Grain-size dependence of electrical properties in (Na0.5Bi0.5)0.94Ba0.06TiO3 films by PLD

Journal of Materials Science: Materials in Electronics - Grain size has significant effects on dielectric and ferroelectric properties of ferroelectric thin film for capacitors applications. In...