GaSe Layers Research Articles

Interaction of GaSe with GaAs(111): Formation of heterostructures with large lattice mismatch

We have studied the epitaxial growth of GaSe, a layered van der Waals material, on GaAs, a zinc-blende-structure semiconductor. This heterostructure exhibits a 6% lattice mismatch, and is a prototypical example of van der Waals epitaxy, where the weak van der Waals interaction allows the misfit to be accommodated without the formation of electronically active defects. GaSe was supplied to the growing surface from a single GaSe Knudsen cell. Reflection high energy electron diffraction and x-ray photoemission spectroscopy studies of the nucleation of GaSe indicate Se reacts with the GaAs surface to remove the surface dangling bonds prior to GaSe formation. This is followed by the oriented growth of stoichiometric GaSe layers, that are rotationally aligned with the underlying GaAs substrate. The termination of the GaAs dangling bonds most likely occurs by Se substitution for As in the surface layer of GaAs(111) B and by direct bonding of Se to surface Ga on GaAs(111) A surfaces. In addition, photoemission measurements indicate that the subsurface Se uptake into the GaAs(111) A lattice is higher than that in the (111) B lattice.

The GaSe/Si(111) interface: a core level study

A heterostructure, prepared by molecular beam deposition, of the layered compound GaSe onto Si(111)1 × 1H has been characterised by ultraviolet photoelectron spectroscopy upon sequential thermal erosion in ultrahigh vacuum. In the temperature range investigated (370–570°C), several steps were observed in the evolution of the Ga 3d and Se 3d core level spectra, from the initial GaSe compound to the Si(111)3×3 surface. Decomposition of the core level spectra was used to identify the different contributions of the system. The Ga as well as the Se atoms of the layered compound are in one chemical environment. The contribution of strained GaSe layers that have the lattice parameter of the Si substrate is found before the appearance of Si 2p. The GaSe/Si(111) interface is described by only one contribution and the result is correlated to the structural model of half a strained GaSe layer bonded to Si.

Influence of surface reconstruction on MBE growth of layered GaSe on Si(111) substrates

Very thin GaSe films, about 100 Å thick, have been epitaxially grown by molecular beam epitaxy on differently ordered Si(111) substrates, namely: the clean 7 × 7 reconstructed surface with its dangling bonds, the H-passivated 1 × 1 surface and the Ga-passivated 3 × 3 R30° reconstructed one. For each substrate, the GaSe layer and its interface with Si have been studied by low energy electron diffraction, Auger electron spectroscopy and photoemission yield spectroscopy. Upon sequential removal of the GaSe film by Joule heating in ultrahigh vacuum, it is shown that, (i) the band offsets are not sensitive to the initial surface structure of the substrate, (ii) the uniformity of the GaSe layer and of the Fermi level position is questionable on Si(111) 3 -Ga , (iii) the density of gap states in the GaSe layer increases upon ageing in air.

Formula omitted] heteroepitaxy: the early stages of growth

The epitaxial growth of the layered compound GaSe on three-dimensional materials (GaAs and Si) has already been achieved by several research groups and is often referred to as “Van der Waals epitaxy”. To check this assumption very thin films (approximately half a layer) of GaSe were grown, by molecular beam epitaxy, on HSi(111) substrates. The X-ray standing waves technique was used to determine the structure of the interface. The Ga atoms are located in T sites, straight above top Si atoms, with a SiGa bond length of 2.37 Å. The position of Se atoms was found to be in agreement with the one calculated from GaSe bulk structure. Therefore, and at least for HSi(111) substrates, the GaSe Si(111) heteroepitaxy is in fact a “classical” pseudomorphic epitaxy. Half a GaSe layer is firstly bonded to Si by covalent bonds and Van der Waals growth of GaSe layers occurs in a second stage.

Surface electronic properties of GaSe-covered Si(111) upon UHV thermal desorption of the GaSe epitaxial layer

Clean 7 × 7 reconstructed Si(111) surfaces have been epitaxially covered with a film of layered GaSe. The GaSe layers are parallel to the (111) plane of the Si substrate. Such a sample was sequentially Joule-heated under ultra-high vacuum from room temperature to above 700°C. Upon raising the temperature, the changes of the surface electronic properties were studied by photoemission yield spectroscopy. Several steps in the dissociative desorption of GaSe were observed. The corresponding work function and band offsets as deduced from photoyield results are presented and discussed.

Formation of a thin III-VI compound interfacial layer at ZnTe/znse heterojunction and its effect on energy band discontinuity

Interfacial layers were inserted at the interface of ZnSe and ZnTe in order to reduce both (1) the effect of strain and (2) the valence band discontinuity. The interfacial layer adapted in this study is the III-VI compound (Ga,Se). The layered structure GaSe is favorable for the present work, because it can be a buffer layer to relax the lattice mismatch at the interface. All layers including ZnTe, (Ga,Se) and ZnSe were grown on (100) GaAs substrate by conventional molecular beam epitaxy. The crystal structure of the (Ga,Se) on ZnSe was investigated. The growth of the layered structure GaSe layer on (100) ZnSe was very difficult, though the defect zinc-blende structure Ga2Se3 layer could be easily grown. The defect zinc-blende structure Ga2Se3 was inserted at the interface of ZnSe and ZnTe so that the valence band discontinuity could be modified. The discontinuity was decreased to about 0.1 eV when the thickness of the interfacial layer was about 8A. The current-voltage characteristics were measured for the sample with Ga2Se3 interfacial layer. The structure with Ga2Se3 exhibited the ohmic property. These results suggest that the valence band discontinuity between ZnTe and ZnSe can be reduced by introducing the Ga2Se3 interfacial layer.

Silicon (111) surface properties upon UHV thermal dissociation of a GaSe epitaxial layer

Clean 7 × 7 reconstructed and H-covered 1 × 1 Si(111) surfaces have been epitaxially covered with a film of layered GaSe. The GaSe layers are parallel to the (111) plane of the Si substrate. Such samples were sequentially Joule-heated under ultra-high vacuum from room temperature to above 700°C. Upon raising the temperature, changes of the surface properties were studied by Auger electron spectroscopy, and low energy electron diffraction. Several steps in the dissociative desorption of GaSe were observed at temperatures which depended on the initial silicon surface preparation. It usually leads to a Ga-induced √3 × √3R30° reconstruction before a clean Si (111) surface is recovered.

Excitonic optical nonlinearities and transport in the layered compound semiconductor GaSe.

Dephasing and transient grating experiments in the direct excitonic absorption region of GaSe at low temperatures show that a fast relaxation within the one-dimensionally disordered excitonic band results in band filling being the dominant mechanism of the optical nonlinearity. Correspondingly, we observe a blueshift of the nonlinear signal with excitation density. The temperature dependence of the exciton diffusion constant measured in directions parallel to the GaSe layer planes indicates that temperature-independent scattering (trapping) and scattering by acoustic phonons determine the exciton mobility at low temperatures.

Molecular beam epitaxial growth and characterization of epitaxial GaSe films on (001)GaAs

We have successfully grown GaSe films on (001)GaAs by molecular beam epitaxy (MBE). Each unit layer of GaSe was grown toward the two directions on (001)GaAs, while the epitaxial GaSe films whose c-axis inclined toward the only one direction were obtained by using slightly misoriented (001)GaAs. Furthermore, we characterized the interface between epitaxial GaSe and misoriented (001)GaAs by transmission electron microscopy (TEM), and it was found that the GaSe layers were grown along the 111 plane in the intermediate region of 0.7 nm from the interface and that the obtained film was arranged in γ-type.

Growth of layered semiconductors by molecular-beam epitaxy: Formation and characterization of GaSe, MoSe2, and phthalocyanine ultrathin films on sulfur-passivated GaP(111)

Studies of the sulfur passivation of GaP(111) surfaces with solution treatments, and the subsequent molecular-beam epitaxy growth and characterization of ultrathin films of layered semiconductors on those surfaces are presented in this article. Simple solution passivation procedures allow formation of a S–GaP(111) semiconductor surface which will support the growth of highly ordered layers of GaSe (Eband gap=2.05 eV). These thin GaSe layers then permit the further growth of ordered layers of a semiconductor like MoSe2 (Eband gap=1.0 eV) or an organic dye such as a phthalocyanine. Reflection high energy electron diffraction and angle-resolved x-ray photoelectron spectroscopy have been used to determine the structure and composition of the surface layers formed at each stage of the deposition process. Absorption spectra are used to characterize the band edge and A1,2 exciton energies of the MoSe2/GaSe S–GaP(111) thin films, and the position and shape of the phthalocyanine Q band.

Energy spectrum and effective mass of carriers in the InSe/GaSe superlattice

Within an effective mass approximation the energy spectrum and mass of carriers in the InSe/GaSe superlattice have been calculated. The superlattice belongs to type II: electrons are primarily confined to the InSe layers whereas the holes are mosfly confined to the GaSe layers. The characteristic feature of electronic structure of the superlattice is the existence of minibands of light carriers at the θ point of the Brillouin zone and minibands of heavy carriers at theM point. The dependence of the miniband structure on thickness of layers has been computed. It is shown that the minibands of light and heavy carriers compete with one another in energy. A general conclusion is made concerning the influence of the competition between the minibands on optic and kinetic properties of the superlattice.

Substrate Effects on The Nucleation and Growth of GaSe Layers by Van Der Waals Epitaxy

ABSTRACTEpitaxial thin film multilayers are limited by the need for both lattice and thermal expansion matching. Recently, a new deposition technique, known as van der Waals epitaxy, has been developed to overcome these limitations. Van der Waals Epitaxy (VDWE)promises the ability to deposit multilayers based on the property of interest without being limited by lattice and thermal expansion mismatch. The crystallographic two dimensional metal chalcogenides are characterized by strong covalent bonding within a layer and weak van der Waals bonds between layers. By combining the layered nature of the metal chalcogenides with other layered materials as well as crystallographic 3D materials, oriented single crystal layers can be deposited, resulting in novel structures with atomically abrupt interfaces. However, even with the weak van der Waals bond, substrate/film interactions play a large role in the final structure.To study the substrate/film interaction occurring during van der Waals Epitaxy growth on 3D surfaces, the metal chalcogenide GaSe has been systematically deposited on GaAs(1 11) substrates. To develop an understanding of the interaction of the substratewith the growing film, growth of GaSe on both atomically rough and smooth substrates was studied. Comparison of the information developed through RHEED, TEM and AFM have been used to understand the basic nucleation and growth process as well as the observation and formation of film defects.

Lattice dynamics of a simple GaSe-InSe superlattice

A simple linear chain model is used to calculate the phonon dispersion curves for a superlattice composed of one layer of GaSe and one layer of InSe alternatively stacked along the c-axis. The resultant acoustic modes are essentially averages of the two constituents. Most optical modes are found to be confined in either GaSe layers of InSe layers. However, some low energy-optical modes have contributions from the two constituents.

Electronic states of InSe/GaSe superlattice

Analysis of recent publications revealed an increasing interest in epitaxial growth of InSe/GaSe superlattice. Within the effective mass theory we carried out self-consistent calculations of the confined and itinerant electronic states, potential profile and charge density distribution of InSe/GaSe superlattice, where the InSe layers are the well and the GaSe layers the barrier. Calculations were performed for three types of doping: uniform, modulated in the well, and modulated in the barrier. It has been found that the Coulomb interaction in the well and barrier forces the formation of localized states in the barrier region. The possibility of an insulator-metal transition in InSe/GaSe superlattice is predicted for modulation doping in the barrier and for a doping level n = 10 19 cm -3. A decrease of the barrier height has been found for modulation doping in the well.

Van Der Waals Epitaxy Versus Homoepitaxy of Low Temperature GaAs (111) Layers

ABSTRACTIn the design of GaAs devices, material selection for heteroepitaxy is limited due to the large amount of strain produced by lattice mismatch. To overcome this problem, a new growth method has been proposed called van der Waals Epitaxy (VDWE). This process attempts to decouple the interface through the growth of a van der Waals bonded crystal layer in-between the two materials with dissimilar lattice constants, thereby accommodating the lattice mismatch. Typical van der Waals materials such as GaSe, have hexagonal crystal structures and are grown with the c-axis perpendicular to the surface due to the nature of the bonding. These materials have a low surface energy and are not very reactive. In addition, they are only stable at relatively low temperatures. This poses two constraints to the growth of GaAs on GaSe. Initial experiments were done to investigate the possibility of growing GaAs (111) layers homoepitaxially at temperatures compatible with van der Waals crystals, with high crystallinity and a smooth surface. Twinned growth layers 1.7μm thick, were obtained at 350° C on a GaAs (111)B substrate using MBE. Further experiments looked at homoepitaxial growth on (111)A substrates and at slightly higher temperatures. These results were then compared to GaAs layers grown on GaSe layers in which nucleation occurs on a van der Waals surface as opposed to the covalently bonded GaAs substrate. The relative quality of the layers was analyzed using RHEED and TEM.

Optical Absorption, Reflection, and Dispersion of GaS and GaSe Layer Crystals

physica status solidi (b)Volume 15, Issue 2 p. K109-K113 Short Note Optical Absorption, Reflection, and Dispersion of GaS and GaSe Layer Crystals G. A. Akhundov, G. A. Akhundov Institute of Physics of the Academy of Sciences of the Azerbaidzhan SSR, BakuSearch for more papers by this authorN. A. Gasanova, N. A. Gasanova Institute of Physics of the Academy of Sciences of the Azerbaidzhan SSR, BakuSearch for more papers by this authorM. A. Nizametdinova, M. A. Nizametdinova Institute of Physics of the Academy of Sciences of the Azerbaidzhan SSR, BakuSearch for more papers by this author G. A. Akhundov, G. A. Akhundov Institute of Physics of the Academy of Sciences of the Azerbaidzhan SSR, BakuSearch for more papers by this authorN. A. Gasanova, N. A. Gasanova Institute of Physics of the Academy of Sciences of the Azerbaidzhan SSR, BakuSearch for more papers by this authorM. A. Nizametdinova, M. A. Nizametdinova Institute of Physics of the Academy of Sciences of the Azerbaidzhan SSR, BakuSearch for more papers by this author First published: 1966 https://doi.org/10.1002/pssb.19660150249Citations: 26AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume15, Issue21966Pages K109-K113 RelatedInformation