The permissible optical input power of a semiconductor optical switch/modulator for maintaining high performances was derived by taking account of reduction of internal electric field due to absorption-induced photo-current. It was found that the extinction ratio degrades with the increase of absorbed optical power. The permissible optical input power, at which the extinction ratio decreases 3 dB, was found to be higher than 20 mW for reflection type optical switch/modulator.

A three-terminal quantum device utilizing photon-assisted tunneling in a multilayer structure is proposed and analyzed in terms of its high frequency amplification characteristics. The operation principle of this device includes photonassisted tunneling at the input, formation of a propagating charge wave due to the beat of tunneling electrons and its acceleration, and radiation of electromagnetic waves at the output. Analysis of these operations, discussion of similarities and dissimilarities to classical klystrons, and estimation of the power gain and its frequency dependence are given. A simple example demonstrates that amplification up to the terahertz frequency range is possible using this device.

A new intersectional switch of small size using total internal reflection generated by an electric-field-induced refractive-index-variation in the multiquantum well (MQW) structure is proposed. The intersectional angle is expected theoretically to be more than 10 for the applied field of 32.8 V/µm in GaInAsP/InP MQW waveguide. This switch is expected to be of small size with high speed response, and is integrable monolithically together with integrated lasers.

We have analyzed a very short channel tunneling field effect transistor which uses new heterostructures (CoSi2/Si/CdF2/CaF2) lattice-matched to the Si substrate. In device operation, the drain current from source (CoSi2) to drain (CoSi2) through tunnel barriers (Si) and the channel (CdF2) is controlled by a gate electric field applied to the barrier between the source and the channel through the gate insulator (CaF2). Theoretical analysis shows that this transistor has characteristics similar to those of conventional metal-oxide-semiconductor field effect transistors even with channel lengths as short as 5 nm. In addition, we have estimated the theoretical response time of this transistor and showed the possibility of subpicosecond response.

We estimated the transit time of GaInAs/AlAs double-barrier resonant tunneling diodes (RTDs) oscillating at 0.6–1 THz. The RTDs have graded emitter structures and thin barriers, and are integrated with planar slot antennas for the oscillation. The transit time across the collector depletion region was estimated from measured results of the dependence of oscillation frequency on RTD mesa area. The estimated transit time was slightly reduced with the introduction of the graded emitter, probably due to reduction of the electron transition between Γ and L bands resulted from the low electric field in the collector depletion region.

The linewidth enhancement factor α is analyzed for long wavelength GaInAs/InP laser. The effects of the anomalous dispersion and the free carrier plasma on α are comparable with each other. Calculated α shows strong wavelength dependence, and is about 3.55.6 at 1.551.6 µm, which is in good agreement with experiments.

As THz wave has the advantages of enough resolution and penetration to materials, it has been examined to be used for the imaging system. The propagation distance of THz wave is limited to be short. That is also the advantage for application to the indoor wireless communication etc. For the achievement of the ultra-high frequency oscillator (and concurrently transmitter) device, the properties of small, electronic excitation, the antenna constructed and being on the wafer are important. For the purpose, the Negative differential resistance Dual channel transistor (NDR-DCT) proposed by AIST is utilized. In this paper, as an initial theoretical analysis, we simulated the oscillation frequency of this device at about 100 GHz-1THz within the Terahertz band on which the above applications was expected. The equivalent circuit model of NDR-DCT was shown based on the analogy with the resonant tunnelling diode (RTDs), and the antenna as the resonance circuit part was designed by the numerical analysis. The possibility of the THz oscillation of this device was confirmed. The slit reflector that we proposed can realize the slot antenna on the device effectively and is suitable for three terminal structure semiconductor. its manufacturing is relatively easy.

We report on the analysis and fabrication of vertical PtSi Schottky source/drain metal oxide semiconductor field effect transistors (MOSFETs), which are suitable for combination with quantum effect devices such as resonant tunneling diodes. Analysis was carried out by one-dimensional approximation of the device structure, WKB approximation of the tunneling probability in Schottky barrier tunneling and self-consistent calculation. Theoretical calculation showed good drivability (750 µA/µm) of this device with tOX = 1 nm and tSi = 5 nm. As a preliminary experiment, devices with a Si channel thickness of 8 nm, 20 nm or 30 nm and a vertical channel length of 55 nm were fabricated. Although the drain current at the "on" state was small due to the thick gate oxide of 8 nm, analysis and measurement showed reasonable agreement with respect to the drivability. Based on the results of theoretical analysis, the device drivability can be much improved by reducing the gate oxide thickness.

From the analysis of layer number dependence of response time and current gain, there is a tendency that with decreasing layer number, response time becomes higher and current gain becomes larger. The current gain band-width product , is estimated theoretically to be 640 GHz (current gain is to be 34), when metal layer number is one and layer thickness is 10 Å.

The transistor action with negative differential resistance (NDR) of a nanometer-thick metal (CoSi2)/insulator (CaF2) resonant tunneling transistor is discussed for two transistor structures. These transistors are composed of metal-insulator (M-I) heterostructures with two metallic (CoSi2) quantum wells and three insulator (CaF2) barriers grown on an n-Si (lll) substrate. One of the two structures has the base terminal connected to one of the quantum wells next to the collector, and the other, to one next to the emitter. Although base resistance is high maybe due to the damage caused during the fabrication process, the two transistors show different characteristics, as expected theoretically. Transfer efficiency α (= IC/IE) close to unity was obtained at 77 K for electrons through the resonant levels in M-I heterostructures.

Field induced refractive index variation and the ratio of index to loss variations p' which is an important parameter deciding the loss characteristics of an intersectional optical switch, was analyzed for GaInAs/InP quantum box structure. We found that large index variation and large | p| value(10) with low fundamental absorption, which are required for low insertion loss switch(1 dB), can be attained. Further the usable wavelength range for low loss switching operation is shown to be around 8 nm.

Experimental result and theoretical analysis are reported for bias-voltage dependence of oscillation frequency in resonant tunneling diodes (RTDs) integrated with slot antennas. Frequency change of 18 GHz is obtained experimentally for a device with the central oscillation frequency of 470 GHz. The observed frequency change is attributed to the bias-voltage dependence of the transit time of electrons across the RTD layers, which results in a voltage-dependent capacitance added to RTD. Theoretical analysis taking into account this transit time is in reasonable agreement with the observed results. Voltage-controlled RTD oscillators in the terahertz range are expected from the theoretical results. A structure suitable for large frequency change is also discussed briefly.

This paper theoretically presents that a terahertz (THz) oscillator using a resonant tunneling diode (RTD) and a rectangular cavity, which has previously been proposed, can radiate high output power by the impedance matching between RTD and load through metal-insulator-metal (MIM) capacitors. Based on an established equivalent-circuit model, an equation for output power has been deduced. By changing MIM capacitors, a matching point can be derived for various sizes of rectangular-cavity resonator. Simulation results show that high output power is possible by long cavity. For example, a high output power of 5 mW is expected at 1 THz.

A novel transistor, introducing metal and iusulator and using the quantum interference of hot electrons in the conduction band of an insulator as the operation principle, is proposed. The metal-insulator combination contributes to the reduction of the device size and obtaining high current density, low resistivity, and small capacitance, which result in the decrease of the response time of the device. Also, since this combination has the extremely high conduction band discontinuity, strong quantum interference can be obtained. The static I-V characteristics are analyzed and it is shown that there are multiple peaks useful for a variety of signal processing and logic applications. In addition, since the gradient between each peak and valley in the characteristics is steep, the device used as an amplifier has a high transconductance which contributes to the reduction of the response time. We show the possibility of subpicosecond response (0.2 ps) of this device theoretically.

A novel electronic device named Space Charge Limited Insulator Tetroide (SCLIT), which uses space charge limited current in insulator of a metal-insulator structure is proposed. A possibility for high speed response (fγ1.1 THz) is estimated theoretically. The static characteristics are also shown.

In this study, we propose and fabricate an oscillator array composed of three resonant-tunneling-diode terahertz oscillators integrated with slot-coupled patch antennas, and which does not require a Si lens. We measure the radiation pattern for single and arrayed oscillator, and calculate the output power using the integration of the pattern. The output power of a single oscillator was found to be ～15 µW. However, using an array configuration, almost combined output power of ～55 µW was obtained.

Phase locking with frequency tuning is demonstrated for a resonant-tunneling-diode terahertz oscillator integrated with a biased varactor diode. The tuning range of oscillation frequency is 606-613GHz. The phase noise in the output of the oscillator is transformed to amplitude noise, and fed back to the varactor diode together with bias voltage. The spectral linewidth at least <2Hz was obtained at the oscillation frequencies tuned by the bias voltage of the varactor diode.

We report on the formation technique and the first observation of visible light emission from silicon nanoparticles (<10nm) embedded in CaF22 Iayers grown on Si(111) substrates by using codeposition of Si and CaF2. It is shown that the size and density of silicon particles embedded in the CaF2 layer can be controlled by varying the substrate temperature and the evaporation rates of CaF2 and Si. The photoluminescence (PL) spectra of Si nanoparticles embedded in CaF2 thin films were investigated. The blue or green light emissions obtained using a He-Cd laser (λ=325nm) could be seen with the naked eye even at room temperature for the first time. It is shown that the PL intensity strongly depends on growth conditions such as the Si:CaF2 flux ratio and the growth temperature. The PL spectra were also changed by in situ annealing process. These phenomena can be explained qualitatively by the quantum size effect of Si nanoparticles embedded in CaF2 barriers.