Quantum-Film, Quantum-Wire, and Quantum-Box Lasers

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Staffs

$B!&(BY. Suematsu $B!&(BS. Arai $B!&(BM. Asada $B!&(BM. Watanabe $B!&(BS. Tamura

Visiting Researcher

$B!&(BG. Bacher

Research Student

$B!&(BY. H. Park

Students

$B!&(BK. C. Shin $B!&(BM. Tamura $B!&(BM. Kumazawa $B!&(BS. Kurihashi $B!&(BT. Kojima $B!&(BM. Madhan Raj $B!&(BN. Serizawa $B!&(BX. Y. Jia $B!&(BH. Arima $B!&(BT. Ando $B!&(BS. Peng $B!&(BM. Ito $B!&(BM. Miura $B!&(BH. Nakaya $B!&(BK. Numata $B!&(BS. Tanaka $B!&(BN. Nunoya $B!&(BT. Numaguchi $B!&(BY. 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.

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

  2. 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 = 240 ?m, cavity length L = 60 ?m) under pulsed operation was 180 A/cm2 (Ith = 20 mA), and was 230 A/cm2 under CW condition.

  3. 1.3 ?m-wavelength Multiple Microcavity Laser with narrow groove (0.4 ?m) was fabricated using Cl2/H2 ECR dry-etching, which operated at 77 K under CW optical pumping condition.

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Semiconductor Photonic Devices

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Staffs

$B!&(BS. Arai

Students

$B!&(BT. Takizawa $B!&(BE. Kikuno $B!&(BA. Uchino $B!&(BT. Shimizu $B!&(BM. Kondo $B!&(BY. 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 17 dB 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 1.55 ?m wavelength. Extinction ratios at each output port of 2.3 dB and 2.6 dB were obtained with low switching light power of 5.9 mW at the input fiber end.

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Quantum Coherent Electron Devices

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Staffs

$B!&(BK. Furuya $B!&(BY. Miyamoto $B!&(BM. Suhara $B!&(BS. Tamura

Visiting Researchers

$B!&(BM. Gault $B!&(BH. Yuzurihara

Students

$B!&(BY. C. Kang $B!&(BF. Vazquez $B!&(BH. Hongo $B!&(BN. Kikegawa $B!&(BN. Machida $B!&(BT. Otake $B!&(BD. Kobayashi $B!&(BR. Takemura $B!&(BJ. Yoshinaga $B!&(BT. Oobo $B!&(BH. Toda $B!&(BN. Matsumoto $B!&(BT. Arai $B!&(BK. Sato $B!&(BA. Yamaguchi $B!&(BY. Ikeda $B!&(BY. Nakamura $B!&(BI. Kobayashi $B!&(BH. Nakaya

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A novel ultra high-speed transistor utilizing high-velocity and wave properties of the ballistic electron was proposed and studied from the viewpoint of (1) ballistic transport in GaInAs/InP, in particular, the wave nature of the hot electron, (2) device concept using the wave nature of the hot electron, and (3) detection of hot electron emission by using a scanning probe microscope.

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  1. In order to evaluate the phase coherent length of hot electrons in semiconductors, triple-barrier resonant tunneling diodes were fabricated by OMVPE. The current-voltage (J-V) characteristics were measured at 4.2K and 77K. Measured J-V characteristics were are explained by the theoretical analysis in which the phase breaking process in each well and the contribution of the relaxed electrons to current are taken into account. For double-barrier resonant tunneling diodes, effects of impurities in a well on the energy level broadening are theoretically analyzed and effects of spacer layer thickness were experimentally investigated.

  2. A hot electron double-slit is performed under a magnetic field in a semiconductor. A 40-nm pitch buried double-slit and two segmented collectors are employed. The variation of the collector current is observed, which amplitude has good agreement with theoretical simulation.

  3. The possibility of hot electron detection with a scanning probe microscope is discussed. To this end we have proposed a technique called Scanning Hot Electron Microscopy (SHEM), which allows to obtain both the spatial and energetic distribution of hot electrons in a device. After demonstrating the theoretical possibility of SHEM, we have been able of obtaining some preliminary experimental results, showing the detection of a 4 pA hot electron current. The expected spatial resolution of the technique has also been analyzed theoretically, showing that it is on the same order as for other scanning probe techniques.

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High-Speed Electron Devices Using Nanometer-thick

Metal/Insulator Layered Heterostructures

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Staffs

$B!&(BM. Asada $B!&(BM. Watanabe

Students

$B!&(BT. Suemasu $B!&(BY. Kohno $B!&(BW. Saitoh $B!&(BK. Mori $B!&(BH. Sugiura $B!&(BK. Yamazaki $B!&(BK. Osada $B!&(BM. Tsutsui $B!&(BK. Yoshida $B!&(BK. Okamoto

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Superlattices and ultrathin layers with the combination of metal and insulator were proposed as one of the candidates of the material for ultrahigh-speed electronic devices and optical devices because of the low resistivity of metals, low dielectric constant and wide band gap of insulators and high conduction band offset at metal/insulator heterointerface. A novel transistor using quantum interference in metal/insulator heterostructure has been proposed and it was shown that sub-pico second response can be expected at such devices.

Results obtained up to now are as follows:

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(1) Multiple negative differential resistance (NDR) due to quantum interference of hot electron waves was observed at 300K for the first time in a small area metal (CoSi2)/insulator(CaF2) quantum interference transistor with an emitter size of 0.9$B!_(B0.9 ?m2 fabricated by using electron-beam lithography. This was achieved by reducing voltage drop in collector series resistance.

(2) A novel amplifier device with multilayer heterostructure was proposed. The device is composed of the input part utilizing photo-assisted tunneling and the output part utilizing radiation from a charge density wave modulation at the input. A simple analysis shows that amplification up to the terahertz frequency range is possible in the device.

(3) A very short channel tunneling field effect transistor using new heterostructures (CoSi2/Si/CdF2/CaF2) lattice-matched to Si substrate, was proposed. Theoretical analysis shows that this transistors has characteristics similar to those of conventional MOS-FET even with the channel length of 5 nm.

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Light Emitting Devices Using Semiconductor(Metal)/Insulator

Nanostructures

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Staffs

$B!&(BM. Asada $B!&(BM. Watanabe

Students

$B!&(BT. Matsunuma $B!&(BY. Aoki $B!&(BA. Yamada $B!&(BT. Maruyama $B!&(BY. Isaka $B!&(BY. Maeda $B!&(BJ. Nishiyama

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New type of light emitting devices on Si substrate are investigated using silicon or cobalt silicide super-heterostructures, such as nanocrystals embedded in insulator (CaF2) or CaF2-CdF2 superlattices.

In such structures including insulating materials as quantum barriers, we can expect strong quantum confinement effects, which can lead fascinating changes in the optical properties relative to those of the 3D bulk material.

Results obtained in this research are as follows:

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  1. Visible electroluminescence from nanocrystalline silicon embedded in CaF2 was firstly observed even at room temperature. The white-blue light emissions could be observed by the naked eye at applying voltage of around 10V. The EL spectra was observed from 400 nm-700 nm at room temperature. This range of wavelength corresponds to the energy between fundamental quantized levels of an electron and a hole in a Si quantum box of 1-2 nm in diameter.

  2. Formation technique of nanocrystal Si and CoSi2 in single crystalline CaF2 on Si(111) substrate was developed using co-deposition and two-step growth of Si, Co and CaF2. Metal or semiconductor crystals less than 10 nm in diameter were obtained using this technique. Growth condition dependence of size and density were also clarified.

  3. Intra-subband transition lasers using CaF2-CdF2 superlattices were proposed and analyzed theoretically. The main feature of these material system is the large conduction band discontinuity at heterointerface and its capability of epitaxy on silicon substrate. Threshold current density of lasers with cascaded CdF2 quantum well active region was calculated.

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Processing for Nanometer Structures

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Staffs

$B!&(BK. Furuya $B!&(BS. Arai $B!&(BM. Asada $B!&(BY. Miyamoto $B!&(BM. Watanabe $B!&(BM. Suhara $B!&(BS. Tamura

Visiting Researcher

$B!&(BG. Bacher

Research Student

$B!&(BY. H. Park

Students

$B!&(BT. Takizawa $B!&(BH. Hongo $B!&(BM. Tamura $B!&(BT. Kojima $B!&(BM. Kumazawa $B!&(BS. Kurihashi $B!&(BE. Kikuno $B!&(BH. Tanaka $B!&(BC. Nagao $B!&(BH. Honji $B!&(BX. Y. Jia $B!&(BT. Ando $B!&(BH. Hattori $B!&(BH. Nakaya $B!&(BA. Kokubo $B!&(BS. Tanaka $B!&(BN. Nunoya $B!&(BY. Hayafune $B!&(BH. 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.