We studied Si and Mg doping characteristics in cubic GaN and fabricated a light emitting diode of cubic GaN on a GaAs substrate by metalorganic vapor-phase epitaxy. The diode structure consisted of undoped and Mg-doped GaN stacking layers deposited on Si-doped GaN and AlGaN layers. The electron-beam-induced-current signal and current injection characteristics of this diode structure were measured. There was a peak at the interface between the Mg-doped and undoped GaN in the electron-beam-induced-current signal. This shows successful growth of the p-n junction. Light emitting operation was achieved by currents injected through the conducting GaAs substrate of this diode at room temperature. We observed electroluminescence below the bandgap energy of cubic GaN with a peak at 2.6 eV.

Investigations were carried out on metalorganic-chemical-vapor-deposition (MOCVD)-grown strained AlGaN/ GaN/sapphire structures using X-ray diffratometry. While AlGaN with lower AlN molar fraction (< 0.1) is under the in-plane compressive stress, it is under the in-plane tensile stress with high AlN molar fraction (> 0.1). Though tensile stress caused the cracks in AlGaN layer with high AlN molar fraction, we found that the cracks dramatically reduced when the GaN layer quality was not good. Using this technique, we fabricated a GaInN multi-quantum-well (MQW) surface emitting diodes were fabricated on 15 pairs of AlGaN/GaN distributed Bragg reflector (DBR) structures. The reflectivity of 15 pairs of AlGaN/GaN DBR structure has been shown as 75% at 435 nm. Considerably higher output power (1.5 times) has been observed for DBR based GaInN MQW LED when compared with non-DBR based MQW structures.

A directly modulated LED or SLD (super luminescent diode) is attractive for low-cost lightwave systems such as access networks. This letter experimentally studies a directly modulated SLD followed by a gain-saturated semiconductor optical amplifier (SOA), and shows that the modulation rate is expanded in effect by the use of the gain-saturated SOA. This results from the shortened response time of the SLD due to the ASE light from the SOA and a level-equalizing effect in the gain-saturated SOA.

An ultra-fast optoelectronic decision circuit using resonant tunneling diodes (RTD's) and a uni-traveling-carrier photodiode (UTC-PD) is proposed. The circuit employs two cascaded RTD's for ultra-fast logic operation and one UTC-PD that offers a direct optical input interface. This novel configuration is suitable for ultra-fast decision operation. Two types of decision circuits are introduced: a positive-logic type and a negative-logic type. Operations of these circuits were simulated using SPICE with precisely investigated RTD and UTC-PD models. In terms of circuit speed, 40-Gbit/s decision and 80-Gbit/s demultiplexing were expected. Furthermore, the superiority of the negative-logic type in terms of the circuit operating margin and the relationship between input peak photocurrent and effective logic swing were clarified by SPICE simulations. In order to confirm the basic functions of the circuits and the accuracy of the simulations, circuits were fabricated by monolithically integrating InP-based RTD's and UTC-PD's. The circuits successfully exhibited 40-Gbit/s decision operation and 80-Gbit/s demultiplexing operation with less than 10-mW power dissipation. The superiority of the negative-logic type circuit for the circuit operation was confirmed, and the relationship between the input peak photocurrent and the effective logic swing was as predicted.

A resonant-tunneling-diode (RTD) based sense amplifier circuit design has been proposed for the first time to envision a very high-speed and low-power memory system that also includes refresh-free, compact RTD-based memory cells. By combining RTDs with n-type transistors of conventional complementary metal oxide semiconductor (CMOS) devices, a new quantum MOS (Q-MOS) family of logic circuits, having very low power-delay product and good noise immunity, has recently been developed. This paper introduces the design and analysis of a new QMOS sense amplifier circuit, consisting of a pair of RTDs as pull-up loads in conjunction with n-type pull-down transistors. The proposed QMOS sensing circuit exhibits nearly 20% faster sensing time in comparison to the conventional design of a CMOS sense amplifier. The stability analysis done using phase-plot diagram reveals that the pair of back-to-back connected static QMOS inverters, which forms the core of the sense amplifier, has meta-stable and unstable states which are closely related to the I-V characteristics of the RTDs. The paper also analyzes in details the refresh-free memory cell design, known as tunneling static random access memory (TSRAM). The innovative cell design adds a stack of two RTDs to the conventional one-transistor dynamic RAM (DRAM) cell and thereby the cell can indefinitely hold its charge level without any further periodic refreshing. The analysis indicates that the TSRAM cell can achieve about two orders of magnitude lower stand-by power than a conventional DRAM cell. The paper demonstrates that RTD-based circuits hold high promises and are likely to be the key candidates for the future high-density, high-performance and low-power memory systems.

A clock recovery circuit is a key component in optical communication systems. In this paper, an optoelectronic clock recovery circuit is reported that monolithically integrates a resonant tunneling diode (RTD) and a uni-traveling-carrier photodiode (UTC-PD). The circuit is an injection-locked-type RTD oscillator that uses the photo-current generated by the UTC-PD. Fundamental and sub-harmonic clock extraction is confirmed for the first time with good clock recovery circuit characteristics. The IC extracts an electrical 11.55-GHz clock signal from 11.55-Gbit/s RZ optical data streams with the wide locking range of 450 MHz and low power dissipation of 1.3 mW. Furthermore, the extraction of a sub-harmonic clock from 23.1-Gbit/s and 46.2-Gbit/s input data streams is also confirmed in the wider locking range of 600 MHz. The RMS jitter as determined from a single sideband phase noise measurement is extremely low at less than 200 fs in both cases of clock and sub-harmonic clock extraction. To our knowledge, the product of the output power and operating frequency of the circuit is the highest ever reported for injection-locked-type RTD oscillators. These characteristics indicate the feasibility of the optoelectronic clock recovery circuit for use in future ultra-high-speed fully monolithic receivers.

A clock recovery circuit is a key component in optical communication systems. In this paper, an optoelectronic clock recovery circuit is reported that monolithically integrates a resonant tunneling diode (RTD) and a uni-traveling-carrier photodiode (UTC-PD). The circuit is an injection-locked-type RTD oscillator that uses the photo-current generated by the UTC-PD. Fundamental and sub-harmonic clock extraction is confirmed for the first time with good clock recovery circuit characteristics. The IC extracts an electrical 11.55-GHz clock signal from 11.55-Gbit/s RZ optical data streams with the wide locking range of 450 MHz and low power dissipation of 1.3 mW. Furthermore, the extraction of a sub-harmonic clock from 23.1-Gbit/s and 46.2-Gbit/s input data streams is also confirmed in the wider locking range of 600 MHz. The RMS jitter as determined from a single sideband phase noise measurement is extremely low at less than 200 fs in both cases of clock and sub-harmonic clock extraction. To our knowledge, the product of the output power and operating frequency of the circuit is the highest ever reported for injection-locked-type RTD oscillators. These characteristics indicate the feasibility of the optoelectronic clock recovery circuit for use in future ultra-high-speed fully monolithic receivers.

Waveguide photodiodes (WGPDs) are key devices for high-speed optical receivers in trunk lines because of their potential ability to provide both high efficiency and a high-speed response. We have designed a waveguide photodiode for 40-Gb/s-range optical receivers. The optical coupling characteristics were simulated in detail to optimize the waveguide structure, and the electrodes of the photodiode were designed to form a coplanar transmission line to match the system impedance, which minimized frequency-response degradation. A highly beryllium-doped, low-temperature-grown InGaAs contact layer grown by gas source molecular beam epitaxy was used to reduce the series resistance, and approximately 40% reduction of series resistance was achieved. The fabricated device exhibited both a very high external quantum efficiency of 81% for 1.55-µm light and a sufficient bandwidth of more than 40 GHz. Though we used a simple conventional fabrication process, excellent characteristics were achieved due to the optimized optical design and well suppressed parasitic parameters.

We developed an optical transceiver diode (TRAD) module for bi-directional time-compression-multiplexing (TCM) transmission systems. A wavelength-insensitive structure as a receiver and a low-capacitance configuration in the module provide a high sensitivity. Stable switching of 156 Mbit/s NRZ burst signals between the transmitter and receiver modes is achieved. In addition, it is shown that optical module cost can be further reduced by using passive alignment on a Si bench.

We developed an optical transceiver diode (TRAD) module for bi-directional time-compression-multiplexing (TCM) transmission systems. A wavelength-insensitive structure as a receiver and a low-capacitance configuration in the module provide a high sensitivity. Stable switching of 156 Mbit/s NRZ burst signals between the transmitter and receiver modes is achieved. In addition, it is shown that optical module cost can be further reduced by using passive alignment on a Si bench.

Waveguide photodiodes (WGPDs) are key devices for high-speed optical receivers in trunk lines because of their potential ability to provide both high efficiency and a high-speed response. We have designed a waveguide photodiode for 40-Gb/s-range optical receivers. The optical coupling characteristics were simulated in detail to optimize the waveguide structure, and the electrodes of the photodiode were designed to form a coplanar transmission line to match the system impedance, which minimized frequency-response degradation. A highly beryllium-doped, low-temperature-grown InGaAs contact layer grown by gas source molecular beam epitaxy was used to reduce the series resistance, and approximately 40% reduction of series resistance was achieved. The fabricated device exhibited both a very high external quantum efficiency of 81% for 1.55-µm light and a sufficient bandwidth of more than 40 GHz. Though we used a simple conventional fabrication process, excellent characteristics were achieved due to the optimized optical design and well suppressed parasitic parameters.

We study ultrafast operation of multiple-valued quantizers composed of resonant-tunneling diodes (RTDs) and high electron mobility transistors (HEMTs). The operation principle of these quantizers is based on the monostable-multistable transition logic (MML) of series-connected RTDs. The quantizers are fabricated by monolithically integrating InP-based RTDs and 0.7-µm-gate-length HEMTs with a cutoff frequency of 40 GHz. To perform high-frequency experiments, an output buffer and termination resistors are attached to the quantizers, and the quantizers are designed to accommodate high-frequency input signals. Our experiments show that both ternary and quaternary quantizers can operate at clock frequencies of 10 GHz and at input frequencies of 3 GHz. This demonstrates the potential of applying RTD-based multiple-valued quantizers to high-frequency circuits.

This paper describes the distortion characteristics of an even harmonic type direct converter (EH-DC) used in earth stations for CDMA satellite communications. Direct conversion technique is known as a method to simplify circuit topologies of microwave transceivers. In satellite communications, multi carriers which have high and nearly equal level are provided to a quadrature mixer of the EH-DC. Hence, the third-order intermodulation degrades receiving characteristics. In this paper, we show the relationship between the distortion characteristics and noise figure of the EH-DC for CDMA satellite communication systems. Furthermore, we show NPR of even harmonic quadrature mixers caused by the third-order intermodulation. Experimental results in X-band indicate that the proposed EH-DC has almost the same BER characteristics compared with a heterodyne type transceiver.

We demonstrate a very simple and compact optical transceiver diode module using a passive alignment on a silicon bench with a V-groove. The excess loss caused by the passive alignment of an optical transceiver diode and a flat-end optical fiber is only 0. 6 dB. A high coupling efficiency of -4. 3 dB is obtained. This results in a high responsivity with a wavelength- and polarization-independence of 0. 5 dB over a 70 nm wavelength range and in good laser performance.

Well-defined wavelength distributed feedback laser diodes (DFB-LDs) are required in WDM network systems. Since the EDFA gain bands have been expanded, even more wavelengths are needed for large-capacity dense-WDM transmission systems. A precisely pitch-controlled Bragg grating fabricated by electron beam (EB) lithography is very attractive for realizing these DFB-LDs. This paper describes this precise pitch- and phase-controlled grating delineated by a novel method called weighted-dose allocation variable-pitch EB-lithography (WAVE). In this method, an EB-dose profile for the grating is precisely controlled by a combination of the allocation and weighting of multiple exposures. This enables us to fabricate a precise fixed-pitch grating as well as a flexible grating with a continuously chirped structure. The stitching error at the exposure field boundary, the grating pitch, and the phase shift were evaluated by using a moire pattern generated by superimposing the microscope raster scan and the grating on a wafer. We also estimated amounts of the stitching errors from fabricated and calculated lasing characteristics, and clarified that the affect of the errors on the single-mode stability of LDs is negligible. Precise wavelength controlled λ/4 phase shifted DFB-LDs were successfully demonstrated as a result of both the WAVE method and the highly uniform MOVPE crystal growth.

Different-wavelength distributed feedback laser diodes with integrated modulators (DFB/MODs) are fabricated on a single wafer operate at wavelengths from 1. 52 µm to 1. 59 µm, a range comparable to the expanded Er-doped fiber amplifier gain band. A newly developed field-size-variation electron-beam lithography enables grating pitch to be controlled to within 0. 0012 nm, and narrow-stripe selective metal-organic vapor-phase epitaxy is used to control the bandgap wavelength of laser active layers and modulator absorption layers for each channel. The channel spacing of fabricated 40-channel DFB/MODs is 214 GHz in average with a standard deviation of 0. 39 nm. Very uniform lasing and modulating performances are achieved, such as threshold currents about 10 mA and extinction ratios about 20 dB at -2 V in average. These devices have been used to demonstrate 2. 5-Gb/s transmission over 600 km of a normal fiber with a power penalty of less than 1 dB.

Multicolor light emitting diodes (LEDs) which emit red (R), green (G) and blue (B) light have been realized by stacking a two-color emission part on a single-color emission part. The former part consists of two emissive layers of red and blue light, which can be selected by changing the polarity of applied field. The latter part consists of a single-color emission part which emits green light. The emission from the diode in the whole visible spectral range can be modulated by the combination of applying various voltages to the two-color and to the single-color emission parts, separately.

Recent technologies of organic film devices are reviewed. New technologies of fabrication and characterization of organic thin films, electro-mechanical conversion materials, and applications for electrical and optical devices are discussed. In this review paper, especially organic light emitting diodes, tunneling junctions using polyimide Langmuir-Blodgett films, tunneling spectroscopy and high-density recording, plastic actuators using conducting polymers, molecular self-assembly process for fabricating organic thin film devices are reviewed.

The chirp noise effect in a directly modulated semiconductor laser diode (LD) is experimentally studied. A previous theoretical study reported that, when an LD is directly modulated, turn-on jitter caused by spontaneous emission, combined with chromatic dispersion, becomes a source of noise in fiber transmission and restricts system performance. This paper points out that, on the contrary, imperfection in LD driving circuits causes chirp noise and limits transmission performance in actual systems. Experiments regarding dependence of chirp noise on LD modulation conditions are also presented, which show that a high relaxation oscillation frequency and a short turn-on delay time are preferable from the viewpoint of chirp noise.

The effect of sampling-pulse pedestals, generated by pulse compression, on the temporal resolution in electro-optic (EO) sampling is studied both theoretically and experimentally. Analysis is made on how the pedestals degrade a measurement bandwidth and a temporal waveform. Based on the analysis, a practical guideline on the suppression of pedestals is also given. Gain-switched laser diode (LD) pulses adiabatically soliton-compressed using a dispersion decreasing fiber are used to confirm the theoretical results, and are successfully applied to high-temporal-resolution (>100 GHz) EO sampling measurements.