T. Kawamura

In situ observation of superstructures on InP(0 0 1) surface under hydrogen atmospheric environment with using grazing incidence X-ray diffraction

Abstract Because of the difficulties of using electron-based techniques in the metalorganic vapor-phase epitaxy (MOVPE) environment, an in situ X-ray diffractometer that combines a goniometer and reactor chamber was developed. Consequent measurements of P-rich InP(0xa00xa01) surface grown by MOVPE show the surface has a (2×1) structure. Calculations based on a P-dimer model suggest that this structure is composed of P-dimers whose bonding is parallel to the [ 1 xa01xa00] direction and indicates indium displacement in the second layer.

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.

High-resolution x-ray diffraction analysis of epitaxially grown indium phosphide nanowires

Indium phosphide (InP) nanowires epitaxially grown on InP (111)B were investigated by using grazing incidence x-ray diffraction. A broad scattering at the tail of InP (22¯0) diffraction and an additional peak at the low angle side were observed, showing the formation of nanowires and alloys of the gold catalysts and indium. Scattering intensity along the [11¯0] direction was compared with calculations based on a cylinder model. The best fit was obtained for a 5.5-nm radius with a 2.5-nm deviation, which was smaller than the values determined from the secondary electron microscopy and photoluminescence spectroscopy measurements. This result is explained by an oxide layer on the nanowire sidewalls and the low quantum efficiency of photoluminescence yields for small nanowires since x-ray diffraction directly detects crystalline structure of nanowires.

High-performance EUV/soft X-ray ellipsometry system using multilayer mirrors

A high-performance EUV/soft X-ray ellipsometry system using multilayer mirrors has been developed. A couple of multilayer mirrors were used for the polarizer, and two multilayer mirrors were used for the rotating analyser. The multilayer mirrors were optimized to obtain a medium extinction of about 2000. An extinction ratio of the polarizer up to 10(4) can be achieved by using two multilayer mirrors, and the calculated reflectivity was more than 35%. The calculated error of the optical elements reveals that the error of the polarizer and misalignment optical parts is mainly of the first order, and that of the analyser is of the second order.

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.

Real-time observation of formation of indium phosphide nanowires by means of GISAXS

Real-time observation of InP nanowire formation was performed using grazing incidence small angle x-ray scattering (GISAXS). Prior to the nanowire growth gold colloidal particles were spread on the substrate as the catalyst and annealed at 500 °C. Changes of GISAXS images were clearly observed after annealing, suggesting the formation of molten metal droplets, which were used for nanowire growth. After staring the growth little change except for the increase of GISAXS intensity was observed, suggesting that x-ray scattering from nanowires overlapped with that from the catalysts. From the GISAXS images calculated using a sphere and cylinder model, scattering from the nanowires shows the streak along the qydirection, and that from droplets shows an increase of intensity around the specular reflection, which qualitatively explains the measured GISAXS image after the growth.

Evaluation of size and its distribution of InP nanowires using small angle X-ray scattering and X-ray diffraction at the grazing condition

The structure of vertical InP nanowires on InP (111)B were investigated using grazing incidence X-ray diffraction and grazing incidence small angle X-ray scattering. The size distribution of the nanowires was evaluated from the diffuse scattering at (22~0) diffraction and analyzed using a cylinder model. The average diameter was about 15 nm, which was 10 nm smaller than that in the SEM observation. This can be explained by an oxide layer on the nanowires sidewall. Nanowire height was investigated using grazing incidence small angle X-ray scattering. Sharp streaks along the horizontal axis were observed, suggesting the formation of nanowires with uniform height. Form the distance between streaks, the average height of the nanowires was determined and the length of nanowires was estimated to be about 700 nm, which was consistent with the SEM observation.