T. Haga

Phase diagram of In-Se system and crystal growth of indium monoselenide

Abstract An equilibrium phase diagram of the In-Se system was investigated in detail by differential thermal analysis (DTA). It was confirmed experimentally that the maximum conversion rate of the InSe crystal as the primary crystal is obtained from an In 1.04 Se 0.96 melt. Composition analyses of ingots grown by the Bridgman method were performed using a He + ion Rutherford-backscattering technique (RBS). The results of the analyses were well consistent with the obtained phase diagram. To appreciate the quality of the InSe crystal, X-ray Laue and ion-blocking patterns, and energy dependance of channeled ions were investigated. These studies indicated that the InSe crystals had no mosaic structure. The values of electron mobility and decay time of photo-excited carriers also indicated the strong improvement of crystal perfection by the non-stoichiometric Bridgman method.

Out‐diffusion of Ga and As atoms into dielectric films in SiOx /GaAs and SiNy/GaAs systems

Residual Ga and As atoms in SiOx and SiNy dielectric films deposited on GaAs were investigated by Rutherford backscattering spectroscopy and particle‐induced x‐ray emission techniques. Both Ga and As atoms were detected in the films after high temperature heat treatment, and even in the films as‐deposited. The magnitude of the residual atoms presumably out‐diffused from GaAs substrates was of the order of 1×1019 /cm3. The concentration of Ga atoms prevails over that of As atoms in SiOx/GaAs systems as is generally known, and vice versa in SiNy/GaAs systems after heat treatment. Dynamic behavior of Ga and As atoms in the films as functions of annealing temperature and annealing time cannot be explained by a simple diffusion mechanism. A model is proposed that the damaged layer around the interface of the systems is responsible for the anomalous out‐diffusion phenomena.

Lattice deformation and interdiffusion of InAs quantum dots on GaAs(100)

InAs quantum dots (QDs) on GaAs(100) grown by molecular-beam epitaxy were structurally characterized by ion channeling. Lattice deformation of the InAs QDs and diffusion of Ga atoms into InAs QDs were clearly observed to depend strongly on the InAs coverage. It was revealed that the diffusion is significantly enhanced when the InAs coverage is changed from 1.53 to 1.71 monolayer. During this change, lattice deformation was reduced while the average size (base diameter) of dots was decreased. These phenomena suggest that some growth process change occurred.

Optimal crystal growth condition of ZnSe grown by molecular beam epitaxy

Abstract The crystal quality of ZnSe grown on the (100) GaAs substrate by molecular beam epitaxy is characterized by ellipsometry and the Rutherford backscattering method. The growth rate and refractive index are measured as a function of the beam pressure ratio of Zn and Se molecules and the substrate temperature. It is discussed that the refractive index reflects the degree of packing of atoms in crystal films. The most close-packed ZnSe crystals are grown at the stronger Se beam pressure by several % than the Zn. The optimal crystal growth temperature around 270°C is confirmed by temperature dependence of growth rate and the refractive index. Substrate temperature dependence of the Rutherford backscattering spectra also shows that MBE ZnSe crystals of the best quality are grown near this temperature.

Interdiffusion between InAs Quantum Dots and GaAs Matrices

The existence of interdiffusion between self-assembled InAs quantum dots and a GaAs substrate has been investigated using ordinary Rutherford backscattering which is also useful for determining the value of the average InAs layer thickness. As a result, evidence for the diffusion of Ga atoms into the dot is obtained. Furthermore, spatial distribution of the diffused Ga atoms in InAs dots is suggested.

Volume distributions of InAs/GaAs self-assembled quantum dots by Stranski–Krastanow mode of molecular beam epitaxy

Abstract We studied the volume distributions of dislocation-free InAs/GaAs self-assembled quantum dots obtained by Stranski–Krastanow mode of molecular beam epitaxy. The same scaling function was obtained over a wide range of dot densities. The scaling function indicated that the cluster size fluctuation normalized by the average size is constant for all the quantum dot densities we studied. The resemblance of the scaling function to that of the submonolayer homoepitaxial growth implies that the strain is not the essential factor determining the cluster size distribution of quantum dots. We also describe the prospects for their device applications.

Volume distributions of InAs/GaAs self-assembled quantum dots by Stranski–Krastanow mode

Abstract We studied the volume distributions of dislocation-free InAs/GaAs self-assembled quantum dots obtained by Stranski–Krastanow mode of molecular beam epitaxy, with and without in situ annealing. The same scaling function was obtained over a wide range of dot densities. The scaling function indicated that the cluster size fluctuation normalized by the average size is constant for all the quantum dot densities we studied. The resemblance of the scaling function to that of the submonolayer homoepitaxial growth implies that the strain is not the essential factor determining the cluster size distribution of quantum dots.

Two modes of Ga diffusion into InAs self-assembled quantum dots suggested by ion channeling

Abstract InAs self-assembled quantum dots (SAQDs) is structurally investigated as a function of growth interruption time from 0 to 180 s . Deformation of In increased as growth interruption time increased. Also, a strong correlation between the In deformation and photoluminescence (PL) peak wavelength was found. Deformation of Ga was reduced when the growth interruption time was changed from 0 to 30 s , increased from 30 to 90 s and saturated beyond 90 s . These results suggest a presence of two different mechanisms of Ga diffusion into QDs.

Crystallographic Properties of Closely Stacked InAs Quantum Dots Investigated by Ion Channeling

The crystallographic properties of InAs quantum dots with thin GaAs(<20 nm) intermediate layers have been investigated by ordinary Rutherford backscattering and particle induced X-ray emission measurements. The results reveal that lattice defects of In increase with a decrease in thickness of the GaAs intermediate layers. We also studied the dependence of channeling on the incident energy, and found that five stacked InAs quantum dots with 1-nm-thick GaAs intermediate layers were very different from those with thicker intermediate layers.

Characterization by ion-channeling of ZnSe grown by photo-assisted molecular beam epitaxy

Abstract Improvement in crystallinity of ZnSe crystals grown by molecular beam epitaxy (MBE) under UV light irradiation was assessed by ion channeling. The present study confirmed that UV irradiation during MBE improves the value of X min from 0.10 to 0.07 by reducing the density of lattice imperfections compared to unirradiated samples.