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Activities
Quantum-Film, Quantum-Wire, and Quantum-Box Lasers
Staffs: Y. Suematsu S. Arai M. Asada M. Watanabe S. Tamura
Visiting Researcher: G. Bacher
Research Student: Y. H. Park
Students: K. C. Shin M. Tamura M. Kumazawa S. Kurihashi T. Kojima EM. Madhan Raj N. Serizawa X. Y. Jia H. Arima T. Ando S. Peng M. Ito M. Miura H. Nakaya K. Numata S. Tanaka N. Nunoya T. Numaguchi Y. Hayafune
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GaInAsP/InP strained-quantum-film, -wire, and -box lasers have been studied both theoretically and experimentally.

Results obtained in this research are as follows:
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(1) Temperature dependences of GaInAsP/InP compressively-strained single-quantum-well lasers with quantum-wire (Q-Wire) size active region were measured and compared with those of quantum-film lasers. Lower threshold current as well as higher differential quantum efficiency operation of Q-Wire laser than those of Q-Film laser at a temperature below 193K were obtained. Threshold current density of Q-Wire laser was 43A/cm2 which was almost a half that of Q-Film laser being 85A/cm2.

(2) From temperature dependence of emission wave length of Q-Wire lasers with different wire width, a clear blue shift (20meV for 15nm wire and 10meV for 20nm wire) was observed which was attributed to lateral quantum confinement.

(3) A room temperature CW operation of GaInAsP/InP multiple microcavity laser with etched mirrors was obtained. The threshold current density with broad contact (width W = 240mm, cavity length L = 60 mm) under pulsed operation was 180 A/cm2 (Ith = 20mA), and was 230 A/cm2 under CW condition.

(4) 1.3mm-wavelength Multiple Microcavity Laser with narrow groove (0.4mm) was fabricated using Cl2/H2 ECR dry-etching, which operated at 77K under CW optical pumping condition.
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Semiconductor Photonic Devices
Staffs: S. Arai
Students: T. Takizawa E. Kikuno A. Uchino T. Shimizu M. Kondo Y. Takeuchi
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Semiconductor directional-coupler-type all-optical switching devices with tapered-shape structures were proposed and analyzed by numerical simulations. Moreover a GaInAs/InP multiple-quantum-well directional-coupler-type all-optical switch was fabricated and its low switching power operation was demonstrated.Results obtained in this research are as follows:
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(1)@A semiconductor directional-coupler-type all-optical switch with tapered-shape structures, based on the nonlinear refractive index variation induced by photoexcited carriers, was proposed and its taper-shape dependence was investigated. By the numerical simulation, it is shown that an introduction of tapered-shape structures is effective for the improvement of the extinction ratio. It is also found that this device can drive the signal light of about 17dB higher power than the switching power.

(2)@A GaInAs/InP multiple-quantum-well (MQW) directional-coupler-type all-optical switch utilizing the carrier-induced nonlinearity was fabricated and its low switching power operation was demonstrated at 1.55mm wavelength. Extinction ratios at each output port of 2.3dB and 2.6dB were obtained with low switching light power of 5.9mW at the input fiber end.
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Processing for Nanometer Structures
Staffs: K. Furuya S. Arai M. Asada Y. Miyamoto M. Watanabe M. Suhara S. Tamura
Visiting Researcher: G. Bacher
Research Student: Y. H. Park
Students: T. Takizawa H. Hongo M. Tamura T. Kojima M. Kumazawa S. Kurihashi E. Kikuno H. Tanaka C. Nagao H. Honji X. Y. Jia T. Ando H. Hattori H. Nakaya A. Kokubo S. Tanaka N. Nunoya Y. Hayafune H. Nakamura
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Study of nanometer structure fabrication technique is important for the realization of quantum effect devices such as quantum-wire or -box devices and ballistic electron devices based on wave characteristics of electrons.

Results obtained in this research are as follows:
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(1) A high density InP triangular vertical pillar structure with a period of 40 nm was obtained by combining electron-beam lithography and anodization techniques.

(2) ECR-RIBE etching of GaInAsP/InP was investigated and characterized by PL intensity dependence on the pattern size.

(3) Conditional boundary between the step flow mode and the 2D-nucleation mode in GaInAs/InP OMVPE growth was obtained. Atomically flat terraces with monolayer steps were formed on both of InP and GaInAs surface.

(4) In EB lithography, the size distribution of dense multiple wire patterns (period: 50 nm) formed on EB-resist (ZEP-520) was measured and its deviation was reduced by proximity effect correction.

(5) Electrical properties of nanostructure is demonstrated. Contact current of 100-nm-pitch Cr/Au wire electrodes on GaInAs, and the current passing through the each wire are measured.
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