Nobuo Matsumura

Y-line emission and lattice relaxation in MBE-ZnSe and -ZnSSe on GaAs

The Y-line emission in photoluminescence spectra at 11 K was studied in MBE-ZnSe and -ZnSSe (up to a sulfur content x=0.13) on GaAs. Compared with X-ray diffraction data, the Y-line seems to relate to misfit dislocations, and thus seems a good measure for checking lattice relaxation in ZnSe and ZnSSe epilayers with a sulfur content x 0.05, the reasons for which are discussed.

Preparation of CdTe thin films on Ge substrates by molecular beam epitaxy

Abstract CdTe films were epitaxially grown on (111) and (100) Ge substrates by MBE at substrate temperatures above 200°C in spite of the large lattice mismatch of 13.5%. From X-ray diffraction and intensity of exciton emissions in photoluminescence the quality of the films was found to be the best at 350°C and the J Cd / J Te ratio of 1/1. But some distortion existed in the epitaxial films. Especially, very large strain remained in the grown films on (100) substrates although the surface morphology was smooth. The (111) films were twinned while the (100) films were not. These results suggest that the twinning in every small area relaxes the lattice strain in (111) films.

MBE growth of high quality lattice-matched ZnSxSe1-x on GaAs substrates

We present the optimum growth conditions of lattice-matched ZnSxSe1-x (x ≈ 0.055) by MBE on (100) GaAs substrates. Surface morphology, X-ray diffraction and photoluminescence were investigated, and the optimum growth conditions were revealed as follows: The molecular beam intensity ratio of the group VI to II element is around 2.0 and the substrate temperature is 340 °C. This molecular beam ratio means that the surface coverage fractions of the group II and group VI atoms are the same during growth. It is shown by comparing the photolumunescence spectra that the quality of the ZnSxSe1-x epilayers was higher than that of ZnSe.

Laser irradiation during MBE growth of ZnSxSe1−x: A new growth parameter

Abstract The effects of light irradiation of a He-Cd laser (441.6 nm) on MBE growth of ZnS x Se 1− x ( x =0−0.13) were studied. The growth rates of the epilayers were reduced and the photo-desorption rate constanSts of Zn, Se and S were obtained. In the photoluminescence spectra at 11 K, the intensities of the free exciton emission increased, and thus the crystallinity of the epilayers was found to be improved. The behavior of surface adatoms on the growing surface under laser irradiation is discussed.

Growth of ZnSxSe1−x by MBE on (100)GaAs substrates: Effect of lattice-matching

Abstract ZnS x Se 1− x layers were grown by MBE using Zn, Se and ZnS as source materials. The sulfur mole franction x was varied between 0 and 0.3. The quality of epilayers was found to be improved around the lattice-matching composition to the GaAs substrate ( x =0.055−0.069) judging from the lattice relaxation, FWHM values of X-ray rocking curve and the photoluminescence spectra.

Growth conditions in molecular beam epitaxy for controlling CdSeTe epilayer composition

Summary form only given. CdSe/sub x/Te/sub 1-x//ZnSe quantum-dots structures have a large conduction and valence band offset at an appropriate composition and are expected to be highly-efficient light-emitting material in the green region. However, to our knowledge, there have been very few reports on CdSeTe epilayers. Composition control of II-VI/sub x/VI/sub 1-x/ mixed crystals is difficult because the vapor pressures of VIth elements are high. In this report, the growth conditions were studied for controlling CdSeTe-epilayer composition.

Photo-assisted MBE growth of ZnSe on GaAs substrates

ZnSe epilayers have been grown by photo-assisted MBE on GaAs substrates at various substrates temperatures and under various molecular beam intensity ratios of group VI to group III element. A He-Cd laser with 441.6 mm wavelength was used as a light source. From the temperature dependence of the photo-desorption rate constants, the activation energies of photo-desorption of Zn and Se adatoms from the physical adsorption state (EPZn, EPSs) and from the chemical adsorption state (EC) are obtained, that is, EPZn=7.8 kcal/mol, EPSe=6.7 kcal/mol and EC=16.1 kcal/mol. Thus, the photo-desorption observed is photo-enhanced “thermal” desorption. ZnSe epilayers have been successfully grown at a temperature as low as 150°C. A sharp and strong free-excition emission is observed in photoluminescence spectra at 11 K in the low-temperature grown samples, which shows that the crystallinity is almost comparable with that of the unirradiated epilayer grown at 340°C (the optimum growth temperature without irradiation).

Lattice strain and its effects on energy band structure in MBE-ZnSxSe1−x/GaAs

Abstract ZnS x Se 1− x layers with various compositions ( x = 0−0.13) and layer thicknesses (0.1–3.5 μm) were grown on (100)GaAs by MBE. Lattice strain and its effects on energy band structure of the epilayers are studied. The lattice constants normal to the substrate revealed that the thin layers (0.1-0.3 μm) grew coherently. Splitting and shifting of exciton emissions due to two-dimensional strain were observed, and hydrostatic and shear deformation potentials were determined. The thick lattice-mismatched layers consist of thin coherently grown layers and remaining relaxed layers. The strain in the relaxed layers are affected both by the mismatches of lattice constants and by the difference in thermal expansion coefficients. The residual strain of the epilayers can be determined by the exciton emission energies using the deformation potentials.

Self-Assembling CdSe, ZnCdSe and CdTe Quantum Dots on ZnSe(100) Epilayers

CdSe quantum dots were fabricated on ZnSe(100) epilayers by the molecular beam epitaxy (MBE) and the solid phase reaction method. ZnCdSe quantum dots were prepared by MBE and the atomic layer epitaxial method. CdTe quantum dots were fabricated by alternate supply of Cd and Te beams. Nanoscale surface structures of these self-assembling dots were observed using an atomic force microscope. Broad emissions were observed in the photoluminescence of these capped samples.

Molecular Beam Epitaxial Growth of ZnSSe with Hg-Xe Lamp Irradiation

ZnSSe epilayers were grown by MBE with light irradiation using a Hg-Xe lamp. The free-exciton-emission intensities increased in the photoluminescence spectra of the light-irradiated epilayers, and the sulfur composition also increased. However, the surface morphologies were rough. The irradiated-photon-energy dependence of the above irradiation effects was investigated for the first time, and it turned out that the photons of energy larger than the band-gap energy of the epilayer were responsible for the light-irradiation effects.