Hiroshi Mitsuhashi

Coherent Growth of ZnSe on GaAs by MOCVD

The lattice parameters of ZnSe have been studied for epitaxial layers of different thicknesses grown on GaAs (100) substrates by metalorganic chemical vapor deposition (MOCVD) using dimethylzinc and diethylselenide as source materials. The results indicate that layers thinner than 0.15 µm can grow coherently on GaAs involving strains due to the lattice mismatch between ZnSe and GaAs, while thicker layers contain misfit dislocations introduced by the relaxation of strain.

MOCVD Growth of ZnSxSe1-x Epitaxial Layers Lattice-Matched to GaAs Using Alkyls of Zn, S and Se

ZnSxSe1-x epitaxial layers have been grown on GaAs (100) substrates by metalorganic chemical vapor deposition (MOCVD) using Zn-, S- and Se-alkyls. With this source combination, the premature reaction typically encountered in the conventional MOCVD of zinc chalcogenides using Zn-alkyls and H2S or H2Se can be eliminated. The composition of ZnSxSe1-x is easily controlled by the transport rates of S- and Se-alkyls. High crystalline quality of lattice matched samples is evident from the surface morphology and the line width of double crystal X-ray diffraction.

Characterization of ZnSSe on GaAs by etching and X-ray diffraction

Abstract Zinc sulfoselenide epitaxial layers grown on GaAs substrates have been characterized by etch pit density (EPD) and full width at half maximum (FWHM) of double-crystal X-ray rocking curves. EPD was observed on a (100) ZnS x Se 1- x /GaAs surface. The etching solution of 0.04% bromine-methanol at 3°C was found to work well for EPD measurement. EPD on the ZnSe epilayers was about 10 7 cm -2 for the general growth conditions, but was as low as 10 4 cm -2 for lattice-matched ZnS x Se 1- x epitaxial layers which gave the narrowest FWHM of 13.6 arc sec.

Effects of Lattice Mismatch on Crystallographic Properties of ZnS Grown on GaP and GaAs by MOCVD

The unusual phenomenon that largely lattice-mismatched ZnS layers grown on GaAs by MOCVD show better surface morphology and crystalline quality than less mismatched ZnS layers on GaP has been investigated by X-ray diffraction measurements. The results indicate that this phenomenon can be ascribed to the strain-relaxation taking place at an earlier stage of epitaxial growth on GaAs than on GaP substrates.

p-type carrier concentration control in lithium-doped zinc selenide grown by MOCVD

Abstract Lithium-doped ZnSe epitaxial layers have been grown on GaAs substrates by metalorganic chemical vapor deposition. Tert-butyllithium (TBL) was used as a doping material. Secondary ion mass spectroscopy showed that Li concentrations in ZnSe layers could be altered from 4×10 17 to 4×10 17 cm -3 by variation of the carrier gas flow rate passing through the TBL cylinder. Photoluminescence measured at 4.2 K indicated acceptor concentration increased with TBL carrier gas flow rate. Carrier concentrations N A − N D obtained from C − V measurements increased to about 1×10 15 cm -3 with increasing TBL carrier flow rate.

Confirmation of P-Type Conduction in Li-Doped ZnSe Layers Grown on GaAs Substrates

Hall effect measurements were carried out for Li-doped MOCVD ZnSe layers whose GaAs substrates were removed. This made it possible to obtain the original p-type properties for the layers. Hole concentration, Hall mobility and specific resistivity were 4.1×1016 cm-3, 24 cm2/V s and 6.4 Ωcm, respectively. Furthermore, the characteristics for the GaAs inversion layers, which were changed from semi-insulating to p-type by Zn diffusion from the ZnSe layers, were estimated by comparing the results of samples without GaAs substrates with those with GaAs substrates.

Investigation of Deep Levels and Residual Impurities in Sublimation-Grown SiC Substrates

Deep levels and residual impurities in sublimation-grown n-type SiC substrates are investigated. Three electron trap centers at 0.26, 0.35 and 0.72 eV below the conduction band (CB) are observed in 4H-SiC for the first time by deep-level transient spectroscopy (DLTS). One electron trap center at 0.68 eV below the CB is also observed in n-type 6H-SiC. The trap concentration and capture cross section are estimated. The concentration of residual impurities V, Cr, Fe and Ti are found to be high. The origin of observed trap centers is discussed with respect to the residual impurities and available information.

MOCVD Growth of ZnSxSe1-x Epitaxial Layers Lattice-Matched to GaP Substrates

ZnSxSe1-x epitaxial layers have been grown on GaP (100) substrates by metalorganic chemical vapor deposition (MOCVD). The layer lattice-matched to the substrate shows a better surface morphology and a narrower line width of X-ray diffraction rocking curve.

Lattice matching effect on the luminescent properties of n-ZnSSe on GaAs grown by MOCVD

Abstract Lattice matching effects on Br-doped ZnSSe/GaAs system were studied. A homogeneous image was observed in the lattice matched system ZnS 0.09 Se 0.91 /GaAs by SEM cathodeluminescence (CL), whereas there were many dark spots on CL images for the lattice mismatched ZnSe/GaAs system. The dislocation density on the (100) surface was estimated as 10 8 cm -2 from TEM cross sectional images and 10 7 cm -2 by etch-pit measurement in the lattice mismatch system. The dislocation density decreased to below 10 6 cm -2 from TEM estimation and 10 4 cm -2 from EPD measurement by lattice matching. The photoluminescence (PL) intensity at room temperature for lattice matched ZnSSe was about 10 times larger than that for lattice mismatched ZnSe with the same doping concentration ( n =10 16 cm -3 ). These studies proved that precise lattice matching is needed to obtain crystals which have a high luminescence efficiency.

Approach to in situ characterization of polysilicon surfaces annealed by XeCl excimer laser

An approach to in situ characterization of polysilicon surfaces annealed by a XeCl excimer laser has been investigated by the UV reflectance method and atomic force microscopy which represents a nano-scale surface morphology. The features of the surface morphology were found to be closely connected to the performance of TFT devices.