Close Lattice Match Research Articles

Recent advances in heteroepitaxial Ge/Si(100) and Ge/Si(l 11)

Heteroepitaxial Ge-on-Si could have many applications which include: high mobility p-channel fieldeffect transistors (FETs), large area Ge-based IR or X-ray detectors, or as a substrate for the growth of other epitaxial semiconductors. In particular, the close lattice match between Ge and GaAs and Ge and ZnSe offers a potential for Ge to be used as an interlayer for a GaAs/Si or ZnSe/Si technology.Additionally, with the Si substrate as the "foundation" for further epitaxial semiconductors, thereisa built-in thermal match for any device that must be intimately bonded to Si-based circuitry. Thisis particularly critical in the case of HgCdTe IR focal plane arrays that are indium bump-bonded to aSi multiplexer which will experience thermal cycling in use. This contribution briefly reviews some ofour recent results in the high temperature growth of Ge epitaxial films on Si(100) and Si(l 11) substrates which are being developed for use as a template for HgCdTe/CdZnTe growth.

Liquid phase epitaxial growth and photoluminescence of InAsSb grown on GaSb substrates from antimony solution

The epitaxial growth of lattice-matched InAsSb onto GaSb substrates from Sb solution by liquid phase epitaxy (LPE) has been investigated. Smooth, mirror-like, epitaxial layers of uniform thickness were obtained under close lattice matching conditions with no evidence of substrate erosion. Photoluminescence emission was observed from the material at room temperature in the wavelength region near 4.2 μm, which is of interest for the fabrication of optoelectronic components for use in infrared CO 2 sensors.

Precipitation in and on Polymers

ABSTRACTMineralized biological tissues form by growth of inorganic phases in or on polymers and membranes. This paper discusses the mechanisms for these processes from a bio-mimetic point of view. Mineralization within a polymer or gel can lead to very fine precipitates because particle agglomeration is prevented and solute diffusion rates are low.Localization of mineralization appears to occur in biology by activation of particular surfaces. The possibility is discussed that this may be due to a close lattice match between the spacing of groups on the polymer and the spacing of ions in the mineral. It is shown that this mechanism is unlikely and other possibilities are discussed.

YBa2Cu3O7−x-Y2O3 system and in situ deposition of trilayer heterostructures by coevaporation

We have deposited YBa2Cu3O7−x-Y2O3-YBa2Cu3O7−x heterostuctures by an in situ electron-beam coevaporation technique. Physical and chemical properties of Y2O3 were studied. The deposition conditions for Y2O3 and YBa2Cu3O7−x are completely compatible. The crystal structure of Y2O3 provides a close lattice match with YBa2Cu3O7−x and allows oxygen diffusion through Y2O3, so that heteroepitaxy and the tetragonal-orthorhombic structural transformations of YBa2Cu3O7−x can be achieved. The heterostructures are therefore of high quality. Both the top and the bottom YBa2Cu3O7−x layers are superconducting above 85 K. Tunneling phenomena on junctions fabricated from these trilayers were observed.

Structural aspects of silicon diffusion in quaternary III-V thin-film semiconductors

The InGaAlP quaternary system allows the production of semiconductor lasers emitting light in the visible range of the spectrum. Recent advances in the visible semiconductor diode laser art have established the viability of diode structures with emission wavelengths comparable to the He-Ne gas laser. There has been much interest in the growth of wide bandgap quaternary thin films on GaAs, a substrate most commonly used in optoelectronic applications. There is particular interest in compositions which are lattice matched to GaAs, thus avoiding misfit dislocations which can be detrimental to the lifetime of these materials. As observed in Figure 1, the (AlxGa1-x)0.5In0.5P system has a very close lattice match to GaAs and is favored for these applications.In this work, we have studied the effect of silicon diffusion in GaAs/InGaAlP structures. Silicon diffusion in III-V semiconductor alloys has been found to have an disordering effect which is associated with removal of fine structures introduced during growth. Due to the variety of species available for interdiffusion, the disordering effect of silicon can have severe consequences on the lattice match at GaAs/InGaAlP interfaces.

New approaches in heteroepitaxy and related devices

In recent years epitaxy without close lattice matching has become rather popular. This allows an additional degree of freedom to tailor the heterojunction properties among others which are finding their niches. In this paper three cases will be reviewed. One case deals with a compound semiconductor on an elemental semiconductor having very small lattice mismatch, a case in point being the interesting GaAs/Ge/GaAs system. The second one has to do with compound semiconductors on elemental Si with substantial lattice mismatch. Examples are GaAs, InP, GaSb and InSb on Si substrates. The third case deals with heterojunction systems that would normally exhibit lattice mismatch in their relaxed state. Grown very thin, below a critical thickness, these systems are coherent but strained. For example the InGaAs/(Al,Ga) As system which has been used to produced very high frequency devices and high quality low threshold and/or high power lasers, falls into this category.

Ice Nucleation by Alcohols Arranged in Monolayers at the Surface of Water Drops

Monolayers of aliphatic long-chain alcohols induced nucleation of ice at temperatures approaching 0 degrees C, in contrast with water-soluble alcohols, which are effective antifreeze agents. The corresponding fatty acids, or alcohols with bulky hydrophobic groups, induce freezing at temperatures as much as 12 degrees C lower. The freezing point induced by the amphiphilic alcohols was sensitive not only to surface area per molecule but, for the aliphatic series (C(n)H(2n + 1)OH), to chain length and parity. The freezing point for chains with n odd reached an asymptotic temperature of 0 degrees C for an upper value of n = 31; for n even the freezing point reached a plateau of -8 degrees C for n in the upper range of 22 to 30. The higher freezing point induced by the aliphatic alcohols is due to formation of ordered clusters in the uncompressed state as detected by grazing incidence synchrotron x-ray diffraction measurements. The diffraction data indicate a close lattice match with the ab layer of hexagonal ice.

Effects of electron irradiation on alkaline earth fluorides

Alkaline earth fluorides are important materials in the electronics industry because of their use in the epitaxial growth of semiconductor-on-insulator (SOI) devices. Their main advantages are their close lattice match with the common semiconductors, and the fact that they evaporate as molecular units upon heating which implies good control of film stoichiometry in Molecular Beam Epitaxy. More recently, further interest has developed relating to their use in nanolithography because they are materials which can be suitably patterned with an electron beam in device processing.Moreover, some inorganic fluorides potentially offer inherently higher resolution than resists so far used.Various studies have been made on the effects of irradiation on these Group IIA fluorides. It has also been noted during electron microscope characterization of the SOI structures that these fluorides are very easily damaged. Since image detail is lost, it has been suggested that the fluorides are becoming amorphous.

Electronic Structure Studies of Diamond/Metal Interfaces

ABSTRACTWe have begun to investigate theoretically the electronic properties of several ideal epitaxial interfaces of diamond with Ni and Cu, both of which enjoy a close lattice match. Of particular interest is the mechanism responsible for formation of the Schottky barrier, which is not yet fully understood at the microscopic level. We find that both the barrier height and the chemical bonding at the interface are strongly dependent on interface orientation (i.e., the relative positioning of the two surfaces). For orientations near the minimum total energy geometry, the calculated Fermi level is apparently pinned around 1.7 and 2.1 eV for the (111) and (001) interfaces, respectively, relative to the valence band maximum. For orientations not near the total energy minimum, the calculated barrier height is zero. A tentative explanation for this difference is proposed.

Study of layered and coevaporated V(Mo)N and (V/Si)N films

Layered and coevaporated V/Mo samples were nitrided and their T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> 's and spin-orbit scattering rates were compared. This is of Interest because of the close lattice match of VN with the postulated high T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> of cubic MoN. In no case was a T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> higher than that of VN obtained. The spin-orbit scattering rate was found to be larger in the layered (V/Mo)N samples than in the coevaporated ones. We have compared (V/Mo)N and similarly made (V/Si)N multilayer films with theories for the critical field of such structures. Evidence for dimensional crossover was seen in the parallel critical field curve of (V/Mo)N films. Also, the T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> of thin (V/Si)N multilayers was found to be dependent on the Si layer thickness.

Epitaxial Growth of CdTe on (100) GaAs/Si and (111) GaAs/Si Substrates Using Molecular Beam Epitaxy and Metalorganic Chemical Vapor Deposition

CdTe is a very important semiconductor with versatile applications extending from solar energy conversion to optoelectronics. In addition, both the close lattice match between CdTe and HgCdTe and the immunity of CdTe to autodoping of the HgCdTe make CdTe the substrate of choice for the growth of HgCdTe. However, CdTe is extremely difficult to grow and the nonavailability of good quality, large area, inexpensive, single crystal CdTe has slowed the development of HgCdTe detectors. Infrared device processing requires large areas of single crystal material and the problems associated with CdTe have called for alternative substrates for growing HgCdTe.

II–VI / III–V Heterostructures

ABSTRACTThe integration of several optoelectronic device functions onto a common substrate material is an area which is currently being actively pursued. In an effort to achieve this objective, experiments are under way to examine the epitaxial growth and material properties of a variety of both II–VI and III–V compounds grown on a substrate where the II–VI/III–V heterostructure can be utilized. This paper describes some recent developments involving the molecular beam epitaxial (MBE) growth and characterization of two important II–VI/III–V heterostructures: ZnSe/GaAs and InSb/CdTe;. a comparison is made between epitaxial layer/substrate interfaces and epilayer/epilayer interfaces for both heterostructures. The ZnSe/GaAs heterointerface, having a 0.25% lattice constant mismatch, has potential for use in passivation of GaAs devices. The InSb/CdTe heterointerface possesses an even closer lattice match, ∼0.05% (comparable to the (Al,Ga)As/GaAs material system), and is motivated by possible device applications provided by InSb/CdTe quantum wells.

Bonding of antimony on GaAs(110): A prototypical system for adsorption of column-V elements on III-V compounds

It is shown that the atomic structure of column-V-element overlayers on GaAs(110) is in the form of a zigzag chain arrangement by a combination of detailed experimental investigation (using both photoemission electron spectroscopy and low-energy electron diffraction) and simple theoretical analysis. Antimony (Sb), used as a representative column-V element, spontaneously forms zigzag chains which are parallel to and in registry with the zigzag chains of the GaAs(110) surface when deposited at room temperature. The close lattice match between the size of the GaAs(110) surface unit cell and the zigzag chain constructed with Sb favors a near-ideal (dehybridized Sb orbitals in the Sb---Sb bonds) structure for the adatom chain when bonded to the substrate. The result is a new very-well-ordered atomic arrangement on the surface with two Sb atoms inside the GaAs(110) surface unit cell. From simple calculations, it is shown that the dehybridization of the states of the column-V atom in the zigzag chain structure results in a surprisingly narrow (\ensuremath{\sim}1.5-eV) band of bonding $p$ states, when compared to the \ensuremath{\sim}12-eV bandwidth of bonding $p$ states in a linear chain. Strong evidence for this narrow band of Sb $p$ states is shown in the photoemission data. Two schemes for attachment of the zigzag chain to the GaAs(110) surface are presented and their electronic structure is analyzed. This analysis shows that the states generated by the two attachment schemes fall in the same energy regions, and hence the present combination of photoemission data and simple theoretical analysis does not identify with certainty which scheme is the correct one. However, careful low-energy electron diffraction analysis by Kahn, Duke, and co-workers does favor one attachment scheme over the other. It is concluded that the combination of simple theoretical and detailed experimental approaches employed here are useful, in general, for determining the structure of column-V overlayers on III-V semiconductor surfaces.

In1−xGaxAs-GaSb1−yAsy heterojunctions by molecular beam epitaxy

Smooth films of n-In1−xGaxAs and p-GaSb1−yAsy were grown by molecular beam epitaxy. As a function of the compositions, x and y, the lattice constants vary linearly while the energy gaps show a downward bowing. Abrupt heterojunctions made of these alloys with close lattice matching exhibit a series of current-voltage characteristics which change from rectifying to Ohmic as x and y are reduced. The relative location of the band-edge energies of the two semiconductors at the interface is shown to account for the unusual characteristics observed experimentally.