Jiro Osaka

Crystal growth of completely dislocation-free and striation-free GaAs

Abstract Completely dislocation-free and striation-free, semi-insulating GaAs crystals with 50 mm diameter are grown for the first time by means of the newly developed Czochralski process. These crystals are obtained by combining the following techniques; (i) a dislocation-free seed crystal is used to eliminate grown-in dislocations, (ii) the fully encapsulated Czochralski (FEC) method is applied in combination with indium doping to suppress stress-induced dislocations, and (iii) a vertical magnetic-field is applied to homogenize the distribution of doped indium.

Quantitative analysis of carbon in liquid‐encapsulated Czochralski GaAs

The quantitative analysis of carbon in liquid‐encapsulated Czochralski (LEC) GaAs crystals has been investigated using secondary ion mass spectrometry (SIMS). Localized vibrational mode (LVM) infrared absorption measurements are calibrated by SIMS results. A LVM absorption of 1 cm−2 arisen from carbon was found to be produced by a carbon concentration of 9.5±2.9×1015 atoms cm−3 at room temperature. This carbon LVM optical cross section is 2.7 times larger than the value which had previously been reported. Carbon concentrations in LEC GaAs crystals are estimated to be 1–3×1015 cm−3 or lower.

Homogeneity of Vertical Magnetic Field Applied LEC GaAs Crystal

The effect of a vertical magnetic field on both GaAs melt temperature distribution and the homogeneity of LEC GaAs crystals is studied. It is found that although melt flow fluctuations that introduce irregular striations can easily be eliminated, laminar thermal convection cannot be completely suppressed by the magnetic field. This residual laminar thermal convection degrades both microscopic and macroscopic homogeneity of crystals. However, striation-free crystals having a doped Se concentration variation of less than 2.5% across the wafer are obtained by optimizing the seed rotation rate in the presence of such a magnetic field.

Effective segregation coefficient of carbon impurity in LEC GaAs crystals

Abstract The effective segregation coefficient ( k eff ) of carbon impurity is precisely determined by investigating the 13 C concentration distribution along the growth axis in 13 C doped LEC GaAs crystals. It is concluded that the k eff of carbon impurity is 1.44±0.08, by considering a carbon evaporation rate of approximately 2×10 14 atoms/cm 2 ·h.

A Novel Delayed Flip-Flop Circuit Using Resonant Tunneling Logic Gates

A novel delayed flip-flop circuit using monostable-bistable transition logic elements (MOBILEs) was proposed, and was fabricated using resonant-tunneling-diode/high-electron-mobility-transistor integration technology on an InP substrate. Error free operations at up to 12.5 Gb/s were demonstrated at room temperature.

Ultrahigh-speed circuits using resonant tunneling devices

Ultrahigh-speed circuit applications of resonant tunneling diodes (RTDs) have been developed. One of the key concepts is the merged utilization of RTDs and high electron mobility transistors (HEMTs). The integration technology for InP-based RTDs and HEMTs has been developed. Another key technology developed is a circuit configuration using series-connected RTDs, driven by a clocked bias, in combination with HEMTs. Given this circuit concept, various kinds of edge-triggered flip-flop circuits and multiple-valued quantizers featuring high-speed operation and compact configuration have been constructed. By extending this circuit concept, an optoelectronic circuit using RTDs and a photodiode has also been developed. High-speed operations have been demonstrated, including a delayed-flip-flop circuit operating at 35 Gbit/s, multiple-valued quantizers operating at 10 GHz, a 2-bit analog-to-digital converter operating at 5 GHz and an optoelectronic circuit that demultiplexes an 80 Gbit/s optical signal into a 40 Gbit/s electrical signal. The presented results clearly show the potentiality of RTD-based circuits for the construction of unprecedented ultrahigh-speed communications and signal processing circuits.

High-Speed and Low-Power D-FF Employing MOBILEs (Monostable-Bistable Transition Logic Elements)

l.Introduction Resonant tunneling devices have been considered a possible candidate for the key device in the near future and have therefore been intensively studied in recent years. This is due to the potential for high-speed operation of resonant tunneling devices as well as their high functionality, which leads to lower power dissipation. We have developed a new logic gate, called a MOBILE (monostable-bistable transition logic element), which exploits the negative differential resistance (NDR) of the resonant tunneling phenomenon [1]. High-speed operations up to l8 Gb/s of the MOBILE inverter have been recently demonstrated at room temperature [2). This paper proposes a novel delayed flip-flop (D-FF) circuit using MOBILEs, which has the compatible function with that of the ordinary D-FF and demonstrates a high-speed and low-power operation up to 12.5 Gb/s at room temperature.

A LARGE OUTPUT VOLTAGE SWING OF A RESONANT TUNNELING FLIP-FLOP CIRCUIT EMPLOYING A MONOSTABLE-BISTABLE TRANSITION LOGIC ELEMENT (MOBILE)

A resonant tunneling flip-flop circuit was fabricated based on a monostable-bistable transition logic element (MOBILE). In this work, an Source Coupled FET Logic (SCFL) type output buffer and depletion-mode High Electron Mobility Transistors (HEMTs) were employed instead of a Direct Coupled FET Logic (DCFL) type buffer and enhancement-mode HEMTs used in previous studies. A practical output voltage level close to the SCFL interface was demonstrated for the first time with a MOBILE circuit operating at a high bit rate of up to 20 Gb/s. This indicates that the MOBILE has sufficient current drivability.

Gallium arsenide growth by synthesis, solute diffusion method

High purity GaAs was synthesized by the Synthesis, Solute Diffusion (SSD) method. The growth rate was about 3.0 mm/day at growth temperatures around 930°C and at arsenic pressures above 10-2 atm. The growth rate, and its dependence on arsenic pressure, were analyzed to clarify the growth mechanism. It was concluded that the growth rate is determined by arsenic diffusion in the gallium melt, and the crystal synthesis is suppressed by Ga2O gases produced by the reaction between the gallium melt and the quartz crucible at arsenic pressures below 10-2 atm.

Ultrafast optoelectronic time-division demultiplexer IC using resonant tunneling diodes and a unitraveling-carrier photodiode

A 100-Gbit/s class optical receiver will be required in near-future transmission systems. For realizing such high-speed receivers, an ultrafast electronic device and a wideband photodetector are needed. Resonant-tunneling diodes (RTDs) can offer a switching time of less than a few picoseconds. A new type of wideband photodetector, called unitraveling-carrier photodiode (UTC-PD), has a 150-GHz bandwidth and high saturation power. In this paper, we propose an ultrafast optoelectronic time-division demultiplexer IC using only two RTDs and one UTC-PD. The circuit fabricated monolithically demultiplexed an 80-Gbit/s optical signal into a 40-Gbit/s electrical signal with a power consumption of 7.75 mW.