Yoshinori Nomura

Observation of a large third-order nonlinear response of exciton polaritons in GaAs thin film

We investigated the third-order nonlinear response of excitons in GaAs thin films grown by molecular beam exitaxy. Degenerate four-wave mixing (DFWM) measurements were made using picosecond pulses of 3.2 ps auto correlation width at T=5 K. The DFWM signal of a 110-nm-thick GaAs film at exciton resonance energy is 25 times larger than that of a 1-μm-thick GaAs film. This enhancement is explained by the confinement effect of exciton polaritons, which is due to the nonlocal response of the center-of-mass quantized states of excitons in a radiation field.

Gas source MBE growth of InP

We report the electrical and optical properties of InP epilayers grown by gas source molecular beam epitaxy (GSMBE) using trimethylindium (TMI) and phosphine (PH3) under various growth conditions. Reflection high-energy electron diffraction (RHEED) intensity oscillations during the growth of InP are also described. It is found that high quality epilayers are obtained at about 490°C, and at this temperature the RHEED intensity oscillations with periods of more than 700 are observed.

Optical switch for multimode optical-fiber systems

A new type of optical switch is constructed of graded-index rod lenses. It is operated mechanically by small electromagnets. This switch is compatible with practical multimode-fiber communication systems. It has many outstanding features, such as low insertion loss (1.3–1.4 dB), low crosstalk ( 2 × 106 times), and small size (40 × 50 × 25 mm3).

Observations on intensity oscillations in reflection high‐energy electron diffraction during gas source molecular beam epitaxy of InP

We report the first observation of reflection high‐energy electron diffraction intensity oscillations during the growth of InP using trimethylindium and phosphine in gas source molecular beam epitaxy (GSMBE). By optimizing the growth conditions, intensity oscillations more than 700 periods have been observed. The temperature and flux dependence of the oscillating behavior have been studied. Results indicate that the growth of InP by GSMBE is predominantly via a two‐dimensional layer‐by‐layer mode.

Effect of hydrogen molecules on growth rates of GaAs in gas source molecular beam epitaxy

We observed intensity oscillations of reflection high-energy electron diffraction during growth of GaAs using triethylgallium (TEG) and arsine (AsH3). The oscillation period increased with increasing AsH3 flow rate. We found that introduction of H2 or N2 during the growth also caused a decrease in the growth rate. The growth rate reduction is explained by assuming that transient residence of H2 or N2 molecules on the growing surface impedes adsorption of TEG molecules.

Surface diffusion length during MBE and MOMBE measured from distribution of growth rates

Resumen Optoelectronics Technology Research Laboratory, 5-5 Tohkodai, Tsukuba, Ibaraki 300-26, Japan

Ultrafast optical response of excitons weakly confined in semiconductors

Ultrafast optical responses of excitons weakly confined in thin GaAs films are observed in a degenerate four-wave mixing experiment. The signal decay, which is attributed to the coherent response from the second quantized level of the center of mass motion, exhibits a nonmonotonic size dependence. The experimental results are explained by calculation results from a mode analysis based on the microscopic nonlocal theory. The decay time agrees well with the calculation of the radiative width of the confined excitons. These results show that strong coupling can be achieved between the radiation field and confined excitons by controlling the size of the thin semiconductor film.

Selective embedded growth of InGaAs/InP double-heterostructures by chemical beam epitaxy

Selective embedded growth of the InGaAs/InP double heterostructure in a planar fashion was successfully demonstrated by chemical beam epitaxy (CBE). Channels of 5 to 7 μm wide were formed by wet etching on the InP substrate, giving sidewalls of semiconductor. Layers of InP and InGaAs/InP heterostructures were grown on this patterned substrate at a growth temperature of 525°C. The epitaxial layer has facets that depend on the window orientation of the SiO2 mask with respect to the crystal axis. The morphology of the selectively grown material in the channeled stripe along the [011] direction was very smooth.

Molecular beam epitaxy of GaAs x P 1 - x using low-energy P + ion beam

We describe the epitaxial growth of GaAsxP1-x (0 <x < 0.7) on GaAs(00l) substrates using mass-separated low-energy P+ ions, and Ga and As4 molecular beams. Epilayers have been obtained at growth temperatures(Tg) ranging from 300 to 650° C at P+ ion energies(Ep+) between 50 and 300 eV. We have investigated the growth rate as a function ofEp+, and the film composition as a function of the flux ratio of As4 to P+,Tg andEp+. The sticking coefficient of phosphorus is markedly enhanced by using P+ ion, compared with that of As4. As the flux ratio of As4 to P+ is increased from 0 to 8, the composition ratiox of GaAsxP1-xfilms varies from 0 to 0.5. The composition ratiox decreases slightly with increasingTg from 400 to 650° C, and increases with increasingEp+. Film surfaces are smooth atEp+ below 100 eV, and their morphology is degraded with increasing energy.

Molecular beam epitaxy of InP using low-energy P + ion beam

Abstract InP was grown on Fe-doped semi-insulating InP(100) substrates by a new technique in which phosporus was supplied as a mass-separated low-energy ion beam and indium as molecular beam. The electrical and optical properties of the films grown under various conditions are discussed. The epitaxial growth of InP occured at growth temperatures above 200°C, and high quality InP films were obtained with a P + ion energy of 100 eV. The unintentionaly doped epilayers were n-type. The room temperature carrier concentration and Hall mobility of an InP film growth at 480°C and with a P+ ion energy of 100 eV were 1.3×1016 cm-3 and 3100 cm2⧸V · s, respectively. The as-grown surfaces was smooth without any oval type defects.