Shimomura Kazuhiko

We have proposed the optical deflector using arrayed waveguides that have different refractive index fabricated by MOVPE selective area growth. By placing the asymmetric width of SiO2 mask pattern on both sides of the arrayed waveguide, the thickness of the each waveguide in the array has changed gradually. And the phase change in each arrayed waveguide results the deflection of the light. In this device, we have numerically calculated and fabricated the 1xN multi-mode interference (MMI) star coupler using GaInAs/InP MQW structure to input the light equally for each arrayed waveguide. From the numerical calculation, we obtain 0.42dB fluctuation of the output light power in each waveguide in the 1 x 16 MMI waveguide. In the experiment, we fabricated the 1 x 16 MMI waveguide using GaInAs/InP MQW structure, and 0.88dB fluctuation of the output light was obtained for the 1.56mum wavelength input light. And further, we have numerically calculated the wavelength demultiplexing and switching performance in this device. We have obtained the wavelength dependence of output power in 8 arrayed waveguides that have 1.0% refractive index difference in both sides of the arrayed waveguide. From this analysis, we can exchange the output ports of each wavelength by controlling the refractive index in the arrayed waveguide.

Novel ZnCdSe/BeZnTe type-II superlattices (SLs) are very attractive For active layers of new visible light emitting devices using II-VI compounds on InP substrates. It is expected that the transition energy of the SL can be controlled in a wide visible range from 761 to 397 nut by only changing layer-thickness combinations. In this study, the ZnCdSe/BeZnTe SLs grown on InP substrates by molecular beam epitaxy with the shutter Control method for the first time. In the X-ray diffraction measurements, sharp satellite peaks from the SL structures could be observed, which indicates that high crystal qualities and steep interfaces between ZnCdSe and BeZnTe layers were obtained by using the shutter control method. For the SL samples with several layer-thickness combinations, wide-range visible emissions from 740 to 507 nut could be observed in the Pl measurements at 15 K. The PL peaks are comparable to theoretical transition energies calculated for ZnCdSe/BeZnTe SL structures. A double hetero (DH) structure consisting of ZnCdSe/BeZnTe SLs and BeZnTe cladding layers was fabricated. In the PL spectrum of the DH sample at 15 K. sharp peak emissions at 517 and 614 nm could be observed.

ZnCdSe/BeZnTe II-VI compound superlattices (SLs) were grown on InP substrates by molecular beam epitaxy for the first time. In the X-ray diffraction studies, definite satellite Peaks were observed for each sample, which indicates that fine periodic SL structures were obtained. For SL samples with several layer thickness combinations, wide-range visible emissions from 740 to 507 nm were observed during photoluminescence (PL) studies at 15 K. Comparison of PL emission properties at 15 K for a ZnCdSe/BeZnTe SL and ZnCdSe bulk samples showed the superior emission intensity of the SL sample, A double hetero-structure (DH) consisting of ZnCdSe/BeZnTe SLs and BeZnTe cladding layers was fabricated. In the PL spectrum of the DH sample at 15 K, sharp emission peaks at 517 and 604 nm were observed. Visible light emitting diodes were fabricated by applying ZnCdSe/BeZnTe SLs as the active layer, and were evaluated under pulsed current injections at room temperature. A single-peak yellow-green emission around 562 nm was obtained.

BeZnCdSe quaternaries, MgSe/BeZnCdSe superlattice (SL) and BeZnCdSe quantum well (QW) structures were grown on InP substrates by molecular beam epitaxy for the first time. As for a lattice-matched Be-0.08(Zn0.30Cd0.70)(0.92)Se sample, a single-peak photoluminescence (PL) spectrum was observed at the temperature range from 15K to room temperature. The PL peak wavelength and the full-width at half-maximum (FWHM) value at 15 K were 572 nm and 8.8 meV, respectively. PL measurements of MgSe/BeZnCdSe SL samples were observed single-peak emissions in the green-to-blue color range from 525 to 470 nm at 15 K with changing MgSe layer-thickness ratio from 0.20 to 0.60. As for the QW sample consisting of four BeZnCdSe QWs with a different well width, PL peaks corresponding to each QW were observed in the wavelength range from 459 to 561 nm at 15 E(. By fitting calculated transition energies in the QWs to the PL peak energies. the band offset ratio between the BeZnCdSe well and the MgSe/BeZnCdSe SL barrier was estimated to be DeltaE(c) : DeltaE(v) = 9 : 1. (C) 2001 Elsevier Science B.V. All rights reserved.

We have proposed the optical deflector using arrayed waveguides that have different refractive index by MOVPE selective area growth with asymmetric width of SiO_2 mask pattern on both sides of the arrayed waveguide where the thickness of the each arrayed wavegrade has changed gradually. And the phase change in each arrayed waveguide results the deflection of the light. We have numerically calculated and fabricated the 1×N multi-mode interference (MMI) star coupler using GaInAs/InP MQW structure to input the light equally for each arrayed waveguide. From the numerical calculation, we obtain 0.42dB fluctuation of the output light power in each waveguide in the 1×16 device. In the experiment, 0.88dB fluctuation of the output light was obtained for the 1.56μm wavelength input light. And further, we have numerically calculated the performance of the wavelength divide device by using this arrayed waveguide.

We report the wavelength control of the arrayed waveguide using MOVPE selective area growth. The asymmetric mask pattern, which placed the wide mask next to the one-side-arrayed waveguide, resulted in the gradient change of the bandgap wavelength in array waveguides. The wavelength in each waveguide was found to be linearly changed and clearly dependent on the wide mask width W-w. A 100nm photoluminescence peak wavelength shift in the arrayed waveguide was achieved for a 50 mum asymmetric mask pattern, while maintaining linearly shifted profiles. (C) 2000 Elsevier Science B.V. All rights reserved.

BeZnTe II-VI compound ternary alloys with various Be composition (x(Be)) were grown on InP substrates by molecular beam epitaxy. From absorption coefficient measurements at room temperature. the bandgap energies (E-g) were evaluated as a function of x(Be). The bandgap energy monotonically increases from 2.24 to 3.29 eV when increasing x(Be) from 0 to 0.62 By fitting a quadratic equation in terms of x(Be) to the E-g values, E-g = 2.24(1 - x(Be)) + 4.1x(Be) + 0.1x(Be)(x(Be) - 1) is obtained, and tho bowing parameter is seen to be as small as 0.1eV. Thus, the E-g value of BeZnTe, when the lattice constant is matched to InP, is estimated to be 3.1eV. p-type doped BeZnTe alloys were grown using an RF-radical nitrogen source. A high hole concentration of 4.8 x 10(18) cm(-3) was obtained for a Be0.4Zn0.6Te sample with a wide bandgap of 2.97eV. These results suggest that BeZnTe is very promising for p-cladding layer materials in short wavelength II-VI laser diodes. (C) 2000 Elsevier Science B.V. All rights reserved.

We report the wavelength control of the arrayed waveguide using MOVPE selective area growth. The asymmetric mask pattern, which placed the wide mask next to the one-side-arrayed waveguide, resulted in the gradient change of the bandgap wavelength in array waveguides. The wavelength in each waveguide was found to be linearly changed and clearly dependent on the wide mask width Ww. A 100 nm photoluminescence peak wavelength shift in the arrayed waveguide was achieved for a 50 μm asymmetric mask pattern, while maintaining linearly shifted profiles.

A new type of optical deflector with a graded refractive index region is proposed. For this device, two types of structure, a multielectrode type and a comblike electrode type, have been numerically analyzed using the finite difference beam propagation method to show results :such as the dependence of the deflection angle and the deflection efficiency on the structure. We fabricated this optical deflector using a GaInAs/InP MQW structure, and we confirmed the fundamental optical deflection and the wavelength dependence of the device. (C) 1999 Scripta Technica.

Superlattice quasi-quaternaries (SL-QQs), consisting of MgSe/ZnSeTe short-period superlattices, were grown on InP substrates by molecular beam epitaxy with nitrogen p-doping. By changing the Mg composition (i.e., the layer thickness ratio of MgSe in the superlattice) from 0 to 0.76, the photoluminescence peak energy at 15 K increased from 2.11 to 7.68 eV. The N-doping of MgSe/ZnSeTe SL-QQs was performed by two processes, that is by the modulation-doping into ZnSeTe and by the all-doping. For the modulation-doping, a hole concentration of over 1 x 10(18) cm(-3) was obtained for Mg composition of less than 0.14, with decreased monotonically with increasing Mg composition. The hole concentration increased by changing the doping process from the modulation-doping to the ail-doping. Far example, the hole concentration increased from 1 x 10(15) to 3 x 10(17) cm(-3) for Mg composition of 0.4. ZnCdSe/MgZnCdSe(Te) light emitting diodes (LEDs) were fabricated using MgSe/ZnSeTe SL-QQs as p-cladding layers having yellow emissions around 577 nm at 77 K.

The gate-length dependencies of the optical response characteristics in an optically controlled metal oxide semiconductor field effect transistor (MOSFET) have been measured. This device was fabricated as an integrated structure of the absorption region anti MOSFET region using the direct wafer-bonding technique. By reducing the gate length of the MOSFET region, the transconductance of the FET channel was increased, and a high current modulation and responsivity was obtained by irradiation of 1.5 mu m wavelength light.

We have demonstrated a novel integrated photo- detector on Si large-scale integration circuits, This device integrated the light absorption region on the gate of metal-oxide-semiconductor field-effect transistor (MOSFET), and the long wavelength light controls the current of MOSFET. The GaInAs-InP multiple-quantum-well absorption region and SiO2 of the MOSFET were directly bonded, From the experimental results, we confirmed that the light-controlled current was increased by shortening the gate length of the MOSFET, and that an 1850 A/W responsivity was obtained in a 3.5-mu m gate length device using an irradiation of 1,5-mu m wavelength light.

The gate length dependencies of the optical response characteristics in the optically controlled MOSFET have measured. This device was the integrated structure of absorption region and MOSFET region by using direct wafer bonding technique. By reducing the gate length of MOSFET region, the transconductance of FET channel was increased, and we obtained high current modulation and responsivity by irradiation of 1.5 mu m wavelength light.

New type optical deflector with graded refractive index region has proposed. For this device, two types structure that are multi electrode type and comb like electrode type have been numerical analyzed using Finite Difference Beam Propagation Method, and have shown the structural dependence on the deflection angle and the deflection efficiency, etc. We fabricated this optical deflector using GaInAs/InP MQW structure, and we confirmed the fundamental optical deflection and the wavelength dependence of the device.

High on-off ratio and high responsivity was obtained in a novel integrated optically controlled HEMT, The integrated structure of the device was composed of a p-i-n photodiode region and a HEMT region, These two regions were bonded using direct wafer bonding technique, When a laser light with a wavelength of 1.55 mu m was irradiated on the absorption region, on-off ratio of 12 dB and a responsivity of more than 300 A/W was obtained, This device is very attractive as the high efficiency optoelectronic (OE) transformer directly integrated on the LSI circuits.

ZnCdSe/MgZnCdSe multiple quantum well (MQW) devices were fabricated on InP substrates by molecular beam epitaxy, and quantum-confined Stark effect (QCSE) in the devices were investigated by measurements of reflectance variations at the top surface and absorption coefficient variations in the MQW region with changing applied voltage at room temperature. As a result, remarkable reflectance variations were observed near 587 nm wavelength, accompanied by red shifts of the transition wavelength with increasing applied voltage. A maximum reflectance variation of 5.2% was obtained under the applied voltage of -7.5 V (the electric field of 1.9 x 10(5) V/cm). From the electromagnetic analysis of the device structure. the refractive index variation of 2.4% per well in the MQW was theoretically estimated for the maximum reflectance variation. (C) 1998 Elsevier Science B.V. All rights reserved.

For the first time, high responsivity was obtained from an integrated optically controlled metal-oxide semiconductor field-effect transistor using the direct wafer bonding technique, The integrated structure of the device was composed of an absorption p-i-n photodiode region and a MOSFET, These two regions were bonded using the SiO2-InP direct wafer bonding technique, When a laser light with a wavelength of 1.50 mu m was irradiated on the absorption region, a responsivity of more than 280 A/W was obtained, This is the largest responsivity in an integrated long-wavelength photoreceiver on a Si substrate, This device modulates MOSFET's current by changing the electric field in the absorption region.

We have researched the optical deflectors, which are capable of random access that the optical switches don't have. In the last, we have proposed the refractive index distribution type optical deflectors by the numerical analysis using FD-BPM. We fabricated the GaInAsP/InP MQW waveguide optical deflectors, and measured the deflection characteristics. The structure of the device using GaInAsP/InP MQW wafer consists of the single mode waveguide where the input light propagates, the grated refractive index region whose refractive index changes by applied voltage. We observed 7μm deflection at the input of 1.46μm wavelength 0.3mW light power where the applied voltage was -2V. This result was equivalent to 1 degree deflection angle.

An optically controlled field-effect transistor (FET) in which the GaAs FET region and the GaInAs/InP light absorption region were directly bonded is demonstrated. This device offers high optical-to-electrical conversion efficiency. In this work, we report the electrical and optical characteristics of this device based on the direct wafer bonding technique. The bonding temperature dependence on the device characteristics and responsivity characteristics were also measured. As a result, we achieved a high responsivity of more than 150 A/W.

The purpose of this study is the realization of optical modulator of II-VI MgZnCdSe compounds lattice-matching to InP substrate. In this study, quantum confined stark effect of ZnCdSe/MgZnCdSe multiple quantum well(MQW) grown on InP substrate by molecular beam epitaxy(MBE) was investigated. The reflectance measurement for the MQW structure at room temperature showed the maximum variation of the reflectance at a wavelength near the lowest excitonic transition gap was -6.3% which corresponded to the refractive index venation of -3.4% under 1.87x10^5V/cm electric field apply. This value was larger than that of III-V materials. It is expected that the high performance optical modulator is realized due to the large excitonic effect on II-VI compounds. Fabry-Parot optical modulator which consisted of the spacer layer of the MQW between two multiple layer reflectors were also designed, and the extinction ratio and the insertion loss of the modulator were estimated. Furthermore MgZnCdSe multiple layer reflectors were grown an maximum reflectance of 98.0% was obtained at 596nm

The drain-to-source current of a metal-oxide semiconductor field-effect transistor (MOSFET) was controlled by long-wavelength laser light for the first time. The device studied was composed of an absorption region and a MOSFET, and these two regions were bonded by polyimide. When the voltage was applied to the absorption region, it shelved the normal operation of a MOSFET. When the laser light with a wavelength of 1.48 mu m was irradiated on to the absorption region, a responsivity of more than 100 A/W was achieved. This device modulates the current of the MOSFET by changing the electric field in the absorption region, and it has the possibility of high-speed operation up to 60 GHz.

We have fabricated the optically controlled MOSFET by using direct wafer bonding technique. It was the long wavelength light detector integrated on Si substrate, and we have measured its optical response characteristics. The device modulated the drain-to-source current using the potential change of the light absorption region when the laser light was irradiated. The response speed depends on the light absorption region and the MOSFET and it is possible to use under tens GHz frequency As a resnilt of the measurement, the maximum modulation current ΔI_<DS> of 560μA, the maximum Photo screening voltage ΔV_<PS> of 0.4V, and the maximum responsivity R of 288A/W were obtained, when the input light wavelength was λ=1.50μm.

An optically controlled field-effect transistor (FET) in which the GaAs FET region and the GaInAs/InP light absorption region were directly bonded was demonstrated. The temperature dependence of the direct bonding and its effect on the performance of the optically controlled FET were examined. A maximum current modulation rate of 60% and a responsivity of more than 150(A/W) were obtained.

We have fabricated the optically-controlled FET using direct wafer bonding technique. In this fabrication, we changed the annealing temperature of direct bonding at 620, 660 and 700℃. And we measured the dependence of the annealing temperature of direct banding from the input optical characteristics of the device. As a result, we have achieved high responsivity R=151.8(A/W).