Y Takeda

X-ray ctr scattering measurement of inp/ingaas/inp interface structures fabricated by different growth processes

Hetero-interfaces of InP/InGaAs (three monolayers (ML))/InP samples grown by organometallic vapor phase epitaxy (OMVPE) were investigated using X-ray crystal truncation rod (CTR) measurement. The samples were prepared with three different source-gas flow-sequences: (a) conventional sequence, (b) growth interruption, and (c) Ga and In source-gas pulse injection. The results of the X-ray CTR measurement showed that the interfaces between InP cap and InGaAs layers of (b) and (c) were sharper than that of (a) as intended. However, the amount of As in (b) was less than that designed since As atoms desorbed even from the InGaAs layer during the growth interruption. Surprisingly, the Ga atoms distributed wider and peak compositions of Ga were smaller than those designed for all the samples. It means that the quantum well structures are far from those designed and expected. It suggests that more efforts are necessary to control the distribution of group-III atoms after we solved the problem of group-V atom distributions.

InAs dots grown on InP (001) by droplet hetero-epitaxy using OMVPE

Abstract We have successfully obtained InAs dots on InP (001) by droplet hetero-epitaxy and observed room-temperature photoluminescence (PL) spectrum with a peak at around 1.6 μm. Dependences of the surface morphology on the substrate temperature and on the trimethylindium (TMIn)-supply time were investigated. From atomic force microscopy (AFM), images of the samples prepared by varying the TMIn-supply time, a critical coverage for supplied In to form droplets was found to exist between 1.5 monolayers (MLs) and 3 MLs. This result was confirmed by low-temperature PL measurements. At the TMIn-supply of 3 MLs, which was above the critical coverage, small dots of height ≈5 nm were formed with the density of 9.8x10 9 cm −2 . A PL spectrum of the sample grown using the same sequence followed by the growth of a 10 nm InP cap-layer, exhibited a 1.6 μm emission, with a full width at half maximum (FWHM) of 150 meV at room temperature.

SR-stimulated etching and OMVPE growth for semiconductor nanostructure fabrication

Abstract Synchrotron radiation- (SR-)stimulated etching and selective area growth by organometallic vapor phase epitaxy were performed to form an ordered array of InP crystals on SiO 2 -patterned InP (001) substrate. The SR-stimulated etching was used to pattern the SiO 2 film, because photochemical reaction using SR was expected to provide smooth surfaces, vertical side walls and fine patterning. In the first place, we investigated the basic properties of the SR-stimulated etching by using a mm-size pattern of SiO 2 mask. The etched depth was observed to increase linearly with the irradiation dose. It was found that the etching depth was controlled very accurately. Next, we used μm-size patterns of SiO 2 masks for fabricating the ordered array of InP crystals. In a atomic force microscope image of the sample after etching, a steep side wall was observed. However, the etched surface was not smooth, contrary to our expectation. Moreover, some dust were observed on the surface. From this dust it was found that the SR-stimulated etching had a resolution of ≤100 nm at most.

Layer structure analysis of Er δ-doped InP by x-ray crystal truncation rod scattering

The layer structure and crystal structure of an Er δ-doped layer in InP are analyzed in a one monolayer (ML) level by an x-ray crystal truncation rod (CTR) scattering measurement using synchrotron radiation. The Er δ-doped InP sample is prepared by organometallic vapor phase epitaxy using trimethylindium, tertiarybutylphosphine, and tris(methyl-cyclopentadienyl)erbium as source materials. The analysis is made by comparing the measured CTR spectra and theoretically generated ones assuming four possible crystal structures for the Er δ-doped layers. We reveal that the Er atoms in InP form the rocksalt structure ErP. In the analysis of the crystal structure the x-ray interference plays a vital role. Er distribution in the δ-doped layer is clearly resolved in 1 ML level. It is shown that the Er atoms are well confined in 5 ML(15 A) thickness. The total amount of Er atoms is 0.171 ML, which is quite close to 0.2 ML obtained by Rutherford backscattering measurement on the same sample.

Exafs and X-ray Ctr Scattering Characterization of Er Doped in InP by Omvpe

Er-doped semiconductors are considered to be important for optical communication systems since one of the prominent luminescent peaks of Er is in the minimum absorption region of silica based fiber and wavelength of the luminescence is insensitive to the ambient temperature. In this work, OMVPE grown InP samples uniformly and δ-doped with Er were investigated by EXAFS and X-ray CTR measurements. The EXAFS measurement revealed that the uniformly doped Er atoms in InP grown at 580°C formed NaCl-structure ErP, and at 530°C occupied the In-sites. The X-ray CTR measurement revealed that the δ-doped Er atoms in InP at 530C formed NaCl-structure ErP. In the sample, the total number of Er was analyzed to be about 0.171ML(monolayer), and the FWHM of Er distribution was about 5ML. By comparing the results of PL measurement with those of the EXAFS and the X-ray CTR measurements, it was suggested that the Er atoms on In-sites show high efficiency of luminescence and the Er atoms in the NaCl-structure ErP low efficiency.

Growth mode transition of InGaAs in OMVPE growth on GaP (001)

Abstract We investigated growth of InGaAs with different In compositions on GaP (001) substrates by low-pressure organometallic vapor phase epitaxy (LP-OMVPE). From atomic force microscope (AFM), plan-view transmission electron microscope (TEM), cross-sectional TEM and high-resolution TEM observations, it was found that the growth depended clearly on the ratio of TMIn flow rate to the total flow rate of group-III sources ( x TMIn ). In the low x TMIn region, InGaAs grew as a layer. In the high x TMIn region, on the other hand, island formation took place. At x TMIn =0.5, InGaAs islands were formed by the Stranski–Krastanow (S–K) growth mode.

Local structure study of dilute Er in III-V semiconductors by fluorescence EXAFS.

For understanding the luminescence of Er atoms in III-V semiconductors, OMVPE-grown InP doped with Er has been investigated by fluorescence EXAFS (extended X-ray absorption fine structure) in order to study the local structure around Er atoms. The local structures around the Er atoms doped in InP, with doping as dilute as 3 x 10(12) Er atoms in a 1.5 mm x 1.0 mm spot, were successfully measured by fluorescence EXAFS. The EXAFS analysis revealed that the Er atoms doped in InP above 853 K (which showed low luminescence) formed the rock-salt-structure ErP, while the Er atoms doped in InP below 823 K (which showed high luminescence) substituted on the In site of InP. The dependence of the local structure on growth temperature was observed for the samples doped with 3 x 10(12) atoms and 1.2 x 10(13) atoms of Er.

Occupation site and distribution of δ-doped Er in InP measured by X-ray CTR scattering

Atomic level hetero-structure analysis of Er δ-doped InP grown by OMVPE was successfully made by the X-ray crystal truncation rod (CTR) scattering measurement using synchrotron radiation. It was shown that Er atoms in the δ-doped InP formed rocksalt structure ErP. Distributions of the Er atoms around the δ-doped layers were also revealed clearly on the atomic scale. The total amounts of incorporated Er increased exponentially as the Er supply time increased.

X-Ray Interference and Crystal Truncation Rod Observation of GaN and GaInN Layers Grown on Sapphire with AlN Buffer Layer

X-ray CTR measurement was conducted for GaN and GaInN layers grown on sapphire substrates with low-temperature grown AlN buffer layers. It is to study the crystalline structure of the GaN and GaInN layers formed on the sapphire substrates with the buffer layers. The GaN and GaInN/GaN layers on the sapphire substrates with the low-temperature grown AlN buffer layers had the Al polarity ((0001)A). The surfaces were found to be covered with N. The thicknesses of the GaInN layers were measured accurately to be 4.02nm and 40.5nm for the samples designed to have 4nm and 40nm-thick GaInN layers, respectively. Indium compositions for 4nm- and 40nm-thick GaInN layers were determined to be 8.8% and 11%, respectively.

Nanometer-scale InAs islands grown on GaP (001) by organometallic vapor phase epitaxy

We have successfully grown nanometer-scale InAs islands on GaP (001) by low-pressure organometallic vapor phase epitaxy (LP-OMVPE). Effects of substrate temperature and InAs deposition rate on the shape, size and areal density of InAs islands were investigated by ex-situ atomic force microscope (AFM) and high-energy electron diffraction (HEED). The AFM observations showed that the island size decreased with the substrate temperature while the areal density increased, indicating that migration play a role on island formation. The HEED patterns provided significant result that the island grown at high temperature (650°C) consisted of a few grains, while the island grown at low temperatures (550 and 500°C) was single crystalline.