Seiji Fujikawa

Metalorganic vapor-phase epitaxial growth and characterization of vertical InP nanowires

Highly dense and free-standing InP nanowire structures of vertical orientation were grown by the metalorganic vapor-phase epitaxial technique using colloidal Au nanoparticles as the catalyst. Scanning electron microscopy and transmission electron microscopy showed that the nanowires were single crystalline with 〈111〉 growth direction and of uniform length of about 700 nm, and most of them had diameter in the range of 20–25 nm. Photoluminescence measurements, carried out at room temperature as well as at 77 K, showed a significant blueshift in the peak position compared to bulk InP due to the quantum confinement of the carriers in the nanowires. The successful growth of these nanowires opens up the possibility of realizing various nanoscale devices on the wafer scale in the bottom-up approach.

In situ Real-Time X-ray Reciprocal Space Mapping during InGaAs/GaAs Growth for Understanding Strain Relaxation Mechanisms

In situ real-time X-ray diffraction measurements during In0.12Ga0.88As/GaAs(001) epitaxial growth are performed for the first time to understand the strain relaxation mechanisms in a lattice-mismatched system. The high resolution reciprocal space maps of 004 diffraction obtained at interval of 6.2 nm thickness enable transient behavior of residual strain and crystal quality to be observed simultaneously as a function of InGaAs film thickness. From the evolution of these data, five thickness ranges with different relaxation processes and these transition points are determined quantitatively, and the dominant dislocation behavior in each phase is deduced.

Real-time observation of anisotropic strain relaxation by three-dimensional reciprocal space mapping during InGaAs/GaAs (001) growth

Real-time three-dimensional reciprocal space mapping (3D-RSM) measurement during In0.12Ga0.88As/GaAs(001) molecular beam epitaxial growth has been performed to investigate anisotropy in relaxation processes along [110] and [1¯10] directions caused by α and β misfit dislocations (MDs). Anisotropies, strain relaxation, and crystal quality in both directions were simultaneously evaluated via the position and broadness of 022 diffraction in 3D-RSM. In the small-thickness region, strain relaxation caused by α-MDs is higher than that caused by β-MDs, and therefore crystal quality along [110] is worse than that along [1¯10]. Rapid relaxation along both [110] and [1¯10] directions occurs at almost the same thickness. After rapid relaxation, anisotropy in strain relaxation gradually decreases, whereas crystal quality along [1¯10] direction, presumably due to β-MDs, becomes better that along [110] direction and the ratio does not decay with thickness.

Real-time observation of surface morphology of indium phosphide MOVPE growth with using X-ray reflectivity technique

Abstract The results of real-time X-ray reflectivity measurements of MOVPE grown indium phosphide surface are presented. At the low growth temperature of 450°C, large decreases of reflectivity were observed, suggesting the formation of indium islands. At higher growth temperature of 550°C, only small changes were observed at high growth rate, indicating the step-flow growth mode. Oscillations longer than mono-layer growth were also observed at 500°C and 550°C, and roughness changes obtained from these oscillations were less than 0.01-nm, suggesting small islands formation on the terrace or step-edge fluctuation during the growth.

Structural Changes Caused by Quenching of InAs/GaAs(001) Quantum Dots

Self-assembled InAs/GaAs(001) quantum dot structures before and after quenching were investigated by in situ X-ray diffraction to assess the effects of quenching. Before quenching, quantums dots were uniform in size so that the shape and internal lattice constant distribution of a quantum dot were quantitatively determined on the basis of three-dimensional X-ray intensity mapping. X-ray measurements after quenching revealed that the quantum dot size showed a bimodal distribution as a result of the proliferation of dislocated islands during quenching. A formula to describe the X-ray diffraction from dislocated islands with a large size distribution is presented. The cooling rate between 20 and 40 K/min was found to have little effect on the structures of quenched quantum dots.

Real-Time Analyses of Strain in Ultrathin Silicon Nanolayers on Insulators during Thermal Oxidation

In-plane strain in ultrathin silicon nanolayers of separation by implantation of oxygen wafers was characterized in real time by the grazing incidence X-ray diffraction during thermal oxidation in a newly developed oxidation furnace. The strain in the ultrathin silicon nanolayer during the growth is on the order of 10-4. The amount of strain does not change for the thicknesses of 6 nm to about 2 nm, but it increases twofold at the thicknesses of less than 2 nm at the oxidation temperature of 1220 °C. The strain originates from the volume difference between the Si nanolayers and SiO2.

Reconstruction of an InP(001) surface grown by metalorganic vapor phase epitaxy in atmospheric hydrogen environment

A reconstructed surface of InP (001) substrate, grown by metalorganic vapor phase epitaxy under atmospheric hydrogen environment, is investigated by using grazing incident x-ray diffraction. Fractional-order diffractions of (n/2 m) were observed, showing the existence of a (2×1) domain on the surface. Calculations based on the P-dimer model suggest that there are P dimers whose bonding is parallel to the [110] direction and indium displacement in the second layer.

Real-Time Observation of Fractional-Order X-ray Reflection Profiles of InP(001) During Step-Flow Growth

Fractional-order X-ray reflection profiles of (2×1)-InP(001) have been observed for the first time during step-flow growth of metalorganic chemical vapor deposition. Changes of the profiles have revealed that the coverage of (2 ×1) structures during the growth depends on the flow rates of indium and phosphorus sources. After stopping the growth, a slow recovery of peak intensity was observed with a time constant of lager than 1 min which corresponds to the residence time of indium atoms on the surface.

Optical and structural properties of InP nanowires grown under vapor-liquid-solid mechanism by metal organic vapor phase epitaxy

Metal organic vapor phase epitaxial growth of surface mounted and vertically aligned InP nanowires under the vapor-liquid-solid mechanism is being reported in this paper. Two types of the nanowires were grown by using the suspended Au nanoparticles of 10 and 20 nm nominal diameters as the catalyst and their structural and optical properties were compared. Scanning electron microscopy showed the growth of isolated, of uniform cross section along the length and the large number of nanowires per unit area in range of 7-10/spl times/10/sup 9/ cm/sup -2/ for both the Au nanoparticles used. The distribution in the diameters of the nanowires grown using the 10 and 20 nm Au nanoparticles were in the ranges of 5-110 and 5-60 nm, respectively, with the average length of 700 nm, irrespective of the type of the catalysts used. Transmission electron microscopy showed the <111> orientation of the nanowires with the presence of alternate rotational twin structures along the length. Energy dispersive X-ray analysis was carried out for elemental analysis of a single nanowire. The nanowires showed clear room temperature photoluminescence spectra with the peaks blue shifted by 25 and 32 meV due to the quantum confinement of the carriers in the nanowires grown on 10 and 20 nm Au nanoparticles, respectively. The successful growth of these nanowires will help in realizing the wafer scale fabrication and integration of new electro-optic devices under the bottom-up approach.

In situ Study of Strain Relaxation Mechanisms During Lattice-mismatched InGaAs/GaAs Growth by X-ray Reciprocal Space Mapping

The in situ X-ray reciprocal space mapping (in situ RSM) of symmetric diffraction measurements during lattice-mismatched InGaAs/GaAs(001) growth were performed to investigate the strain relaxation mechanisms. The evolution of the residual strain and crystal quality were obtained as a function of InGaAs film thickness. Based on the results, the correlation between the strain relaxation and the dislocations during the film growth were evaluated. As a result, film thickness ranges with different relaxation mechanisms were classified, and dominant dislocation behavior in each phase were deduced. From the data obtained in in situ measurements, the quantitative strain relaxation models were proposed based on a dislocation kinetic model developed by Dodson and Tsao. Good agreement between the in situ data and the model ensured the validity of the dominant dislocation behavior deduced from the present study.