MEE Growth Research Articles

Complete spontaneous avascular necrosis of the adult navicula associated with Mee's growth arrest lines of the great and second toenails

Spontaneous total avascular necrosis of the tarsal navicula has been well documented in children (Kohler's disease) but is uncommon in adults where partial necrosis is usually seen after trauma or in Müller-Weiss disease. A case of spontaneous complete navicular osteonecrosis in a 46 year old female is described; she had accompanying Mee's leuchonychial lines in the toenails of the great and second toes only; the lines resolved after 9 months. She has been treated with an excision of the navicula and interpositional iliac crest bone graft talo-cuneiform fusion with resolution of her pain. It is postulated that the combination of the Mee's lines and avascular necrosis of the navicula indicates an occlusion of the dorsalis pedis in a predisposed individual.

Activity modulation MEE growth of 2H‐AlN on Si(111) using double buffer layer grown by PA‐MBE

AbstractAs a demonstration of the activity modulation migration enhanced epitaxy (AM‐MEE) heteroepitaxial 2H‐AlN thin films of 53.8 nm and 171.3 nm thickness on Si(111) on a double buffer layer (DBL) have been grown by the AM‐MEE of plasma assisted molecular beam epitaxy (PA‐MBE) method. It is a droplet free growth and an atomic layer epitaxy (ALE). The influence of the DBL, which was formed in a MBE chamber before the AM‐MEE growth of 2H‐AlN thin films on Si(111), was studied to improve the crystallinity of AlN films. For the growth of high quality 2H‐AlN on Si(111), the optimization of growth of the DBL. The interface roughness of the DBL as a layer between two layers of AlN and Si, AlN/DBL/Si was characterized by grazing incidence X‐ray reflectivity (GIXR) and the surfaces were observed by AFM. Full width at half maximum (FWHM) of ω /2θ for 53.8 nm and 171.3 nm thickness AlN (0002) films were 12.1 arcmin and 7.1 arcmin, respectively. AFM images showed droplet free growth after the AM‐MEE and importance of the preparation of initial clean Si surface. Unifrom formation of DBL on a large size wafer of Si was available to use indirect exposure of N radical atoms. By increasing the thickness of the AlN the crystallinity was improved but the surface roughness of AlN did not depend on the thickness of the AlN films obtained by fitting results of GIXR curves. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Effect of Interface-Related Deep Levels on high Sensitivity of Schottky Diode Photodetector Based on Ultrathin InGaAs Film on Si

AbstractRecently, the Fermi level has been demonstrated to be pinned in GaAs semiinsulating ultrathin (<100 A) films grown at low temperatures [1]. This allows one to construct a detector with “internal” photocurrent amplification. The amplification effect compensates losses in sensitivity due to the small width of light-sensitive layer which absorbs 10 — 50 % of incident radiation. We fabricate photodetector structures with external quantum efficiency more than 1 for visible region. Photogenerated carriers in the GaAs layer are effectively separated by the built-in electric fields formed by the Schottky barrier and by the charge at the GaAs/Si interface. In this work, we show the relationships between spectral sensitivity of the metal-InGaAs/Si structures and In content. We observed the red shift in the photocurrent spectra with increasing In concentration, although photosensitivity of such structures dropped drastically. This shift demonstrates that the thin InGaAs film is actually responsible for photosensitivity. Despite the low photoluminescence intensity, the lowtemperature PL spectra indicate that band gap decreases with indium flux rising during MEE growth. The surprise was that the decrease of the film thickness caused the increase of photosensitivity. The GaAs(20 A)-InGaAs (20 A)/Si structure was the most sensitive one. We also observed high quantum efficiency in near-UV region (up to 0.8). We determined activation energy of elctron and hole traps and their concentration profiles by DLTS. The centers localized on interface between polar and nonpolar semiconductors are responsible for Fermi-level pinning in III-V semiinsulating materials and act as an electron trap with activation energy 0.59 eV. The origin of deep levels is discussed.

Optical properties of InAs/AlSb superlattices grown by gas source molecular beam epitaxy

InAs/AlSb superlattices (SLs) have been studied by gas source molecular beam epitaxy/gas source migration enhanced epitaxy (GSMBE/GSMEE). Reflection high-energy electron diffraction (RHEED) intensity oscillation measurements show that In and Sb atoms move toward the surface during MEE growth through the exchange process of constituent atoms, although the movement of In atoms can be reduced by lowering the growth temperature. Raman scattering measurements on the InAs/AlSb SLs show that the formation of atomically controlled heterointerfaces is difficult. However, PL (photoluminescence) measurements show that the optical properties of InAs/AlSb quantum wells (QWs) depend strongly on the shutter sequences at the interfaces. 77 K PL from the QWs with InSb-type interfaces is much stronger than that with AlAs-type interfaces, and their temperature variation of the former is much weaker than that of the latter.

Beating in RHEED oscillations observed during MEE growth of ZnSe

Beating in RHEED oscillations observed during MEE growth of ZnSe

Beating in RHEED oscillations observed during MEE growth of ZnSe

We have made the first observations of beating in RHEED oscillations occurring during MEE growth of ZnSe. From measurements of the beat frequency, we have determined the amount of ZnSe deposited per MEE cycle as a function of Zn and Se deposition times and substrate temperature. A unique feature of the ZnSe oscillations is that the amount of ZnSe deposited in each MEE cycle saturates as the Zn and Se deposition times are increased. The saturated amount deposited per MEE cycle depends on the substrate temperature. For example, the saturated deposition amounts are 0.68 monolayers/cycle at 220°C and 0.39 monolayers/cycle at 340°C. We have also investigated thermally-induced and electron-beam-induced desorption by examining the effects, on the per-cycle deposition amounts, of varying the electron beam intensity, and of varying the time between Zn and Se depositions.

Migration Enhanced Epitaxy of GaAs Studied by Reflection High Energy Electron Diffraction and Scanning Tunneling Microscopy

AbstractMigration enhanced epitaxy (MEE) of GaAs on (001) GaAs substrates was studied by reflection high energy electron diffraction (RHEED) and scanning tunneling microscopy (STM). In MEE, Ga and As species are alternately deposited on the growing surface. Ga adatom migration can be enhanced by the low arsenic pressure environment. The STM study was performed ex-situ by the arsenic capping and decapping procedure. We have demonstrated the correlation between the peak RHEED specular intensity during MEE growth and the variation of the lateral step density on the surface, even though the surface stoichiometry changes repetitively during MEE. The peak RHEED intensity during MEE is inversely dependent on the surface step density. The MEE surface exhibited a lower step density than the MBE surface, as shown by both RHEED and STM. However, the MEE surface still exhibited a much higher step density than a well-annealed surface. Consequently we believe that to achieve an atomically flat interface, annealing at high temperature in an arsenic flux is still necessary even if MEE is employed.

Gas source MEE growth of InGaAs/InP superlattices

InGaAs/InP heterostructures having atomically controlled interfaces are grown by gas source migration-enhanced epitaxy (GS MEE) on (001)InP substrates at 350°C. RHEED intensity oscillations persisted for over 1 h with the same amplitude and phase during the growth of InGaAs and InP for appropriate supply times of Group III and Group V atoms and proper supply interruption times. The RHEED intensity traces during the growth of InGaAs/InP superlattices as well as Raman spectra from InGaAs/InP quantum well structures suggest the formation of tailored InGaAs/InP heterointerfaces.

InSb/CdTe heterostructures grown by MBE

InSb/CdTe heterostructures were grown by MBE, including a 10 layer “superlattice”. The structures were characterized by X-ray diffraction, van der Pauw measurements, and SNMS depth profiling. The interfaces widen because of interdiffusion and through the formation of an interface compound from the reaction of Te with the InSb surface. The interface compound is identified as strained InTe(II). The interfaces are still too wide for practical devices. Thermochemical analysis indicates that the reaction can be suppressed by applying a Cd overpressure. The diffusion of In and Sb in CdTe is very fast and will necessitate a MEE growth scheme at lower temperatures.

Application of Reflectance Difference Spectroscopy (RDS) to Migration-Enhanced Epitaxy (MEE) Growth of GaAs

Differences in the reflectance of light polarized along the [110] and [11̄0] directions of the (001) GaAs surface are detected with a simple optical setup and used as an in-situ analysis and control tool for migration-enhanced epitaxial growth. The reflectance difference (RD) signals during successive surface exposures to Ga and As4 beams at various substrate temperatures are analyzed and correlated to the surface reconstruction and the fractional surface coverage, on the basis of current models of the (001) GaAs surface and nucleation of Ga–Ga dimers. A new negative component of the RD signal is tentatively attributed to Ga nucleation and accumulation along [110] terrace edges. Finally, RD periodic signal analysis during a stationary MEE growth process is used to determine the most appropriate growth conditions.