A pitch of a grating drawn by an electron beam was controlled precisely within 10 by attaching an attenuator to a conventional electron-beam-exposure system. This technique may be applied for fabrication of a periodic structure for integrated optics.

The electron wave device requires large current density as well as high coherence to increase the speed. This letter describes a relation between the coherence and the current density of the ballistic electron transport. The product of the degree of the coherence and the current density is a constant determined by the electron group velocity. Decrease of the coherence in the direction(s) not essential for the interference increases the current density.

The bandwidth of the single-mode fiber is derived for both the amplitude-modulation and the heterodyne-detection (AM) system and the intensity-modulation and the intensity-detection (IM) system, in case that the spectral width of the light source is much less than the modulation bandwidth. In the wavelength-division-multiplexing system, the bandwidth per carrier wave is given as a function of the wavelength, and also at the zero-dispersion wavelength. In case of IM system, the frequency dispersion of the fiber causes the harmonic distortion of the signal and reduces the bandwidth to about a third of that in case of AM system.

Fabrication of 1.5 µm GaInAsP/InP laser by OMVPE on p-type substrate is reported. Low threshold current density (1.2 kA/cm2) was obtained by reduction of growth time in order to prevent Zn diffusion from substrate. CW operations at room temperature were obtained in buried heterostructure (BH) devices fabricated by OMVPE-LPE hybrid growth method. No degradation was observed after 2000 hours' aging test.

Current-voltage characteristics of triple-barrier resonant tunneling diodes are theoretically analyzed taking phase breaking into account. The peak current in predicted using conventional theories is much smaller, typically by a factor of 1/3000 for a coherent length of 100 nm, than that measured because the incoherent tunneling process is neglected. We take both the coherent and the incoherent tunneling processes into account in the analysis and show that the product of the peak current and the voltage width at half maximum of the peak current is almost constant even when the phase coherent length varies between 50 and 1000 nm. The peak current density increases by two orders of magnitude in the model developed here.

In this paper, we report the fabrication and device characteristics of InP/InGaAs double heterojunction bipolar transistors (DHBTs) with buried SiO2 wires. The SiO2 wires were buried in the collector and subcollector layers by metalorganic chemical vapor deposition toward reduction of the base-collector capacitance under the base electrode. A current gain of 22 was obtained at an emitter current density of 1.25 MA/cm2 for a DHBT with an emitter width of 400 nm. The DC characteristics of DHBTs with buried SiO2 wires were the same as those of DHBTs without buried SiO2 wires on the same substrate. A current gain cutoff frequency (fT) of 213 GHz and a maximum oscillation frequency (fmax) of 100 GHz were obtained at an emitter current density of 725 kA/cm2.

1.55µm GaInAsP/InP BH lasers with multiple p-n current blocking layer were fabricated entirely by low-pressure OMVPE. The undercut portions were filled in a manner similar to mass transport process. The laser shows a threshold current of 48 mA at 300 K under CW operation.

Gain and loss coefficients were determined for GaInAsP/InP (λg1.5 µm) grown by OMVPE from lasing characteristics. Crystal quality of OMVPE GaInAsP/InP was found to be substantially the same as those grown be LPE. Absorption losses of the quaternary active and the binary InP layers were estimated separately.

This letter describes theoretical characteristics of the electron diffraction transistor and its inverter circuit. The electron wave diffraction due to a transverse potential grating is analyzed taking thermally induced dispersions into account. The switching time is estimated as 0.4 ps at 77 K.

Fabrication of GaInAsP/InP heterostructure lasers for 1.5 µm wavelength region by organometallic vapor phase epitaxy are discussed. Results of growth conditions, which were experimentally found important to obtain the low threshold current density (1 kA/cm2) comparable with LPE at 1.5 µm lasing oscillation are reported, such as gas switching at hetero-interfaces, maintenance of constant temperature over the growth of all layers, selection of carrier gas and doping conditions. Furthermore, OMVPE device techniques for buried heterostructure laser operating at CW condition are described. Fabrications and characterization of quantum well structure are also reported.

The feasibility of a new transistor structure was demonstrated through an experimental observation of current gain and voltage gain. The proposed transistor structure is a hot electron transistor without a base layer to minimize scattering. Electron emission from the emitter is controlled using positively biased Schottky gate electrodes located on both sides of the emitter mesa. Monte Carlo simulation shows an estimated delay time of 0.17 ps and low gate leakage current with open-circuit voltage gain over unity. To confirm the basic operation, the device with a 25 nm wide emitter was fabricated. To obtain saturated current-voltage characteristics, the emitter was surrounded by gates and parasitic regions were eliminated by electron beam lithography. The observed open-circuit voltage gain was 25. To obtain a low leakage current, an electron energy smaller than the Γ-L separation was necessary to maintain the ballistic nature of the electron. When the gate-emitter voltage was 0.8 V, the gate leakage current was only 4% of the collector current. Thus voltage amplication and current amplification were confirmed simultaneously.

The potential distribution around a linear array of donor atoms in a semiconductor crystal is calculated, approximating the linear array by a continuous line charge. Two methods are used for the analysis. One is the self-consistent calculation of Poisson's equation and the effective mass Schrödinger's equation, and the other is the Thomas-Fermi approximation. Results of both methods agree very well, and it is shown that it is possible to form a potential distribution as fine as the electron wavelength by appropriate arrangement of the impurity atoms. Arrays of impurity atoms therefore can act as buiding elements for future electron wave devices.

GaInAs/InP MOSFETs were fabricated by organometallic vapor phase epitaxy (OMVPE) for the first time to obtain an effective channel mobility of 900 cm2/Vs comparable to the best data by other growth techniques. For the MOS structure, a native oxide layer was formed by low-temperature (220) oxidation technique using water. Due to potentially high uniformity, OMVPE MOSFET technique could be very attractive in the optoelectronic integrated circuits(OEIC) for optical communication.

The minimum transferable linewidth by X-ray is derived using waveguide analysis. The minimum width is determined by the refractive index of the absorber and does not depend on the X-ray wavelength. Therefore there is an optimum mask aperture size which provides the minimum linewidth. By using Au as the absorber, 8 nm linewidth is attainable.

We investigated collector current spreading in InGaAs single heterojunction bipolar transistors (SHBTs) having a collector thickness of 75 nm. SHBTs were fabricated with three different emitter widths -- 200, 400, and 600 nm -- and the highest cutoff frequency that was obtained was 468 GHz. The relationship between the current density at the highest cutoff frequency and the emitter width could not be used to estimate the current spreading because it was independent of the collector-base voltage. However, the relationship between the current density with the increase in the total collector-base capacitance and the emitter width indicates current spreading in the collector. The current spreading was estimated to be approximately 90 nm.

Fabrication process for narrow emitter along 010 direction in heterojunction bipolar transistor fully drawn by electron beam lithography was studied. Emitter structure of a 100 nm width was formed by using epitaxial structure with 30-nm-thick InP layer of emitter. Transistor operation of devices with 0.5-µ m-wide emitter was confirmed. This process can be applied to a buried metal heterojunction bipolar transistor (BM-HBT) with narrow emitter, resulting in high-speed operation of BM-HBT.

Ultimate limit of the bandwidth of the multimode optical fiber with the index profile consisting of α-power and the fourth-order terms of radius is derived, rejecting the effects of the cladding and compensating the material dispersion. The 3 dB-bandwidth can be increased up to 1.9 GHz at 10 km length.

The spontaneous emission factor in the rate equation of the injection laser is derived with help of the classical electromagnetic theory. The spontaneous emission is treated as the radiations from dipoles located in the active region. The value of the spontaneous emission factor given theoretically is in good agreement with the measured results. The magnitude of the spontaneous emission factor is inversely proportional to the volume of the active region and the spectral width of the spontaneous emission, and is proportional to the energy confinement factor and the fourth power of the wavelength. The possibility of the suppression of the relaxation oscillation by reducing the volume of the active region is predicted theoretically.

The effect of the intraband electronic relaxation on the relaxation oscillation of the light output from the injection laser modulated directly is examined theoretically. Assuming the k-selection rule, carriers are devided into two parts; that is, carriers which contribute to the laser gain directly, and the rest. The intraband electronic relaxation is taken into account as the coupling of the two parts of the carriers in rate equations. As the result of the small signal analysis of rate equations, the height of the resonance-like" peak in the frequency response of the direct modulation depends on the electronic relaxation time remarkably in the range from 10-13 to 10-12 s. The intraband electronic relaxation possibly concerns with the suppression of the relaxation oscillation of the light output from the GaAs injection lasers.

A method to estimae the coupling length of the fiber in which modes couple each other due to the random bending of fiber axis is given. The coupling length is estimated from the comparison of the measured transfer function to the theoretical one which is derived previously. The coupling length of a graded-index fiber is estimated to be about 0.8 km using this method. Further, the coupling length of recent graded-index fibers is presumed to be about several Km. For step-index fibers, it is estimated to be in the range between 0.5-5 Km.