Koichi Sugiyama

Optical constants of CuGaSe2 and CuInSe2

The complex dielectric functions, e(E)=e1(E)+ie2(E), of chalcopyrite semiconductors CuGaSe2 and CuInSe2 have been measured by spectroscopic ellipsometry in the photon energy range between 1.2 and 5.3 eV at room temperature. The measurements are carried out on the surface parallel to the optic axis c, which allow the determination of the optical properties for light polarized perpendicular (E⊥c) and parallel to the c axis (E∥c). The measured e(E) spectra reveal distinct structures at the lowest direct gap (E0) and higher energy critical points. These spectra are analyzed on the basis of a simplified model of the interband transitions. Results are in satisfactory agreement with the experimental data over the entire range of photon energies. Dielectric-function-related optical constants, such as the complex refractive index n*(E)=n(E)+ik(E), absorption coefficient α(E), and normal-incidence reflectivity R(E), of these semiconductors are also presented.The complex dielectric functions, e(E)=e1(E)+ie2(E), of chalcopyrite semiconductors CuGaSe2 and CuInSe2 have been measured by spectroscopic ellipsometry in the photon energy range between 1.2 and 5.3 eV at room temperature. The measurements are carried out on the surface parallel to the optic axis c, which allow the determination of the optical properties for light polarized perpendicular (E⊥c) and parallel to the c axis (E∥c). The measured e(E) spectra reveal distinct structures at the lowest direct gap (E0) and higher energy critical points. These spectra are analyzed on the basis of a simplified model of the interband transitions. Results are in satisfactory agreement with the experimental data over the entire range of photon energies. Dielectric-function-related optical constants, such as the complex refractive index n*(E)=n(E)+ik(E), absorption coefficient α(E), and normal-incidence reflectivity R(E), of these semiconductors are also presented.

Lattice deformations and misfit dislocations in GaInAsP/InP double‐heterostructure layers

Lattice deformations and misfit dislocations are studied by x‐ray double‐crystal diffraction and topography for GaInAsP/InP double‐heterostructure layers epitaxially grown on (001) InP substrates. No misfit dislocation was observed at the interfaces when the misfits Δa⊥/a between the lattice constants normal to the wafer surface of GaInAsP (0.4 μm thick) and InP layers are within about 5×10−3. The unit cell of the GaInAsP epitaxial layer is tetragonally deformed due to the interface lattice misfit such that the lattice constant parallel to the wafer surface is nearly invariant across the GaInAsP/InP interfaces in the DH wafers both with and without misfit dislocations for ‖Δa⊥/a‖<6.4×10−3.

RHEED Study of InSb Films Grown by Molecular Beam Epitaxy

The surface structures of InSb films grown on (111)A, (111)B and (001)-oriented InSb substrates by molecular beam epitaxy were investigated in situ with a reflection high-energy electron diffraction technique, and the dependences of the surface reconstructions on the relative arrival rates of Sb and In and the surface temperature are reported. The change in surface structures on the (111)B and (001) faces occurs when the Sb/In ratio is about unity, and the ratio at transition does not depend on the substrate temperature. This behavior is interpreted as meaning that the sticking coefficient of Sb atoms (or molecules) is nearly unity for the Sb/In ratio cong1.

Properties of CdTe films grown on InSb by molecular beam epitaxy

Abstract The optical and electrical properties of molecular beam epitaxial layers of CdTe grown on InSb(001) substrates at 200–225 °C and either doped with copper, arsenic, antimony or indium or undoped were investigated. Non-intentionally doped layers are found to be n type and to contain indium and antimony atoms out diffused from the substrates. For copper- and arsenic-doped layers, acceptor-bound exciton annihilation lines become dominant in the exciton region of the photoluminescence spectra at 6 K, whereas for antimony-doped layers the acceptor-bound exciton line remains weaker than the donor exciton line even at antimony concentrations of up to 1.2 × 10 18 cm -3 . P-type conduction was observed only in heavily copper-doped samples.

Orientation effects in the LPE growth of GaInAsP quaternary alloys

It was found that the liquidus composition determined by the saturation technique for the (100) ‐oriented InP source crystal is different from that for the (111) B‐oriented InP source crystal in the LPE growth of GaInAsP alloys. The lattice‐matching conditions in GaInAsP LPE growth using the liquidus data are also influenced by the substrate orientation.

Vapor Phase Epitaxial Growth and Characterization of Ga1-yInyAs1-xPx Quaternary Alloys

Epitaxial layers of Ga1-yInyAs1-xPx alloys have been grown on GaAs substrates using an AsH3-PH3-Ga-In-HCl-H2 chemical vapor deposition system. The influence of mole ratios Ga/(Ga+In) and P/(As+P) in the input gas stream on the alloy composition of epitaxial layers has been investigated. As for the group V elements, the deposition probabilities of As and P species in gas phase are approximately equal for small y, but As deposition appears to become dominant for large y. As for group III elements, Ga is always incorporated more preferentially than In. The lattice constant of the quaternary alloys is ascertained to obey Vegards law and the composition dependence of the bandgap, obtained from photoluminescence measurements, is compared with an interpolation formula, derived by use of the bowing parameters of ternary alloys.

Photoluminescence of GaxAl1-xAs Crystals Grown by Liquid Phase Epitaxy

Photoluminescence studies are made for GaxAl1-xAs mixed crystals doped with Te, Sn, Si, Ge and Zn. Broad low energy emission bands as well as near bandgap emission bands are observed. The near gap bands show changes in characteristics due to the transition from direct to indirect bandgap at composition (1-x)cong0.36. The low energy bands can be classified into two types. Bands of the first type are observed in the direct gap region and arise from the same origin as in GaAs. Bands of the second type are observed both in the indirect and direct gap regions except for small (1-x). From the composition dependence, it is suggested that the bands of the latter type are associated with the deep donor levels induced from the [100] conduction band minima.

Molecular beam epitaxy of InSb films on CdTe

Abstract Heteroepitaxial growth of InSb by molecular beam epitaxy (MBE) on (001)-oriented CdTe substrates has been investigated. Double crystal X-ray diffractometry and Auger electron spectroscopy have shown that single crystal layers of InSb can be grown nearly coherently on the substrates and without interfacial reaction at growth temperatures of 225–275°C.

Photoluminescence of CuAlxGa1−xSe2 crystals grown by chemical vapor transport

The photoluminescence (PL) characteristics have been studied for the CuAlxGa1−x Se2 chalcopyrite quaternary crystals grown by an iodine transport technique. The PL measurements at 77 K reveal the existence of three types of emission bands, which are attributed to transitions involving localized states: shallow acceptors, deep donors, and deep acceptors, respectively. The origin of the shallow acceptors is tentatively assigned to Se interstitials and that of the deep donors to iodine impurities. All the measured crystals are p type and the hole mobility at room temperature decreases with x (≲0.3).

Growth of CuGaSe2 single crystals by the traveling heater method

Abstract Growth of CuGaSe 2 chalcopyrite crystals by the traveling heater method (THM) with In solvent has been investigated. The In solutions saturated with stoichiometric CuGaSe 2 solute at temperatures above 850 °C are single phase, but those saturated below 850 °C are found to be separated into two liquid phases. Bulk single crystals have been obtained by the THM growth at 870–980 °C, but the grown crystals become inevitably solid solutions CuGa x In 1− x Se 2 with several per cent CuInSe 2 1− x = 0.04−0.07 , due to the use of In as the solvent.