Eitaro Ishimura

Improvement of InP crystal quality grown on GaAs substrates and device applications

We have investigated the effect of strained-layer superlattice (SLS) buffer layers on the crystal quality of InP grown on GaAs substrates. The various SLSs such as In0.63Ga0.37As/InP, In0.73Ga0.27As/InP, In0.9Ga0.1P/InP, and GaAs/InP were tested. It is found that the optical property of InP layers grown on In0.63Ga0.37As/InP SLSs was dramatically improved. An InGaAsP/InP double heterostructure laser diode and an InGaAs PIN photodiode (PD) on InP/GaAs with an In0.63Ga0.37As/InP SLS have been fabricated. The CW threshold current of the laser at room temperature was as low as 31 mA, and the dark current of the PD was 30 nA at - 10 V.

Simple planar structure for high-performance AlInAs avalanche photodiodes

We demonstrate a high-performance AlInAs avalanche photodiode (APD) based on a novel planar diode concept. The APD features a simple planar structure without a guardring, which simplifies production making it more like a PIN photodiode process. Measured device characteristics designed for 10-Gb/s use were a dark current of 0.16 /spl mu/A, responsivity of 0.88 A/W, and a gain-bandwidth product of 120 GHz. Reliability was guaranteed by an aging test exceeding 2400 h, whose conditions were a reverse dark current of 100 /spl mu/A at 175/spl deg/C. These features and performance indicate that the AlInAs APD is highly practical.

Long-Wavelength Receiver Optoelectronic Integrated Circuit on 3-Inch-Diameter GaAs Substrate Grown by InP-on-GaAs Heteroepitaxy.

A monolithic long-wavelength receiver optoelectronic integrated circuit (OEIC), which integrates an InGaAs PIN-photodiode (PD) and a GaAs field-effect transistor (FET), has been successfully fabricated on a 3-inch-diameter GaAs substrate using InP-on-GaAs heteroepitaxy, by metalorganic chemical vapor deposition (MOCVD) and conventional GaAs-IC process technology. The epitaxial quality of the PD layer has been improved by use of a low-temperature-grown buffer layer, thermal cyclic annealing and an InGaAs/InP strained-layer superlattice. The integrated PD has low dark current of 10 nA at -5 V bias voltage, and exhibited stable operation at 175°C. The fabricated receiver OEIC has 1.4 GHz bandwidth and sensitivity of -28.1 dBm at the transmission rate of 622 Mb/s with bit error rate of 10-9, which is applicable to practical subscriber optical communication systems.

Dark current and diffusion length in InGaAs photodiodes grown on GaAs substrates

In0.53Ga0.47As photodiodes grown on GaAs substrates have been fabricated and analyzed. The dislocation density in the InGaAs layer is 2×107 cm−2. A lowest dark current of 3.8×10−4 A/cm2 at 10 V bias is obtained, which is very stable during a bias‐temperature test of Vb=−10 V, T=175 °C, and t=100 h. The quantum efficiency is more than 85% at λ=1.3 μm. This device is expected to be practically used. The dark current has been successfully explained by the thermionic emission and thermionic field emission from traps at midgap. The diffusion length of holes in the InGaAs layer is explained by the recombination at dislocations with the finite recombination velocity of S∼104 cm/s.

Investigation of guardring-free planar AlInAs avalanche photodiodes

We analyze the operation principle and the characteristics of a guardring-free planar AlInAs avalanche photodiode (APD) by computational simulation and experimental results. The simple planar structure is based on a novel epitaxy-junction diode concept and its practical performance for 10-Gb/s optical receivers was successfully demonstrated. Electric field simulations clarified how edge multiplication, which is an inherent problem in APDs, is suppressed in the guardring-free structure. The experimental results, which are current-voltage, capacitance-voltage, and wide-range line scans of responsivity, support the simulation results, and the simulation explains the peculiar characteristics of the experimental results. The computational and the experimental analysis are consistent with one another

3D imaging LADAR with linear array devices: laser, detector and ROIC

This paper introduces the recent development of 3D imaging LADAR (LAser Detection And Ranging) in Mitsubishi Electric Corporation. The system consists of in-house-made key devices which are linear array: the laser, the detector and the ROIC (Read-Out Integrated Circuit). The laser transmitter is the high power and compact planar waveguide array laser at the wavelength of 1.5 micron. The detector array consists of the low excess noise Avalanche Photo Diode (APD) using the InAlAs multiplication layer. The analog ROIC array, which is fabricated in the SiGe- BiCMOS process, includes the Trans-Impedance Amplifiers (TIA), the peak intensity detectors, the Time-Of-Flight (TOF) detectors, and the multiplexers for read-out. This device has the feature in its detection ability for the small signal by optimizing the peak intensity detection circuit. By combining these devices with the one dimensional fast scanner, the real-time 3D range image can be obtained. After the explanations about the key devices, some 3D imaging results are demonstrated using the single element key devices. The imaging using the developed array devices is planned in the near future.

40G RZ-DQPSK transmitter monolithically integrated with tunable DFB laser array and Mach-Zehnder modulators

A 40G RZ-DQPSK transmitter monolithically integrated with a tunable DFB laser array and Mach-Zehnder modulators was developed for the first time. The optical waveform of 40Gb/s DQPSK was successfully demonstrated.

Hybrid integration of waveguide photodiode and preamplifier IC using Au stud bump

The authors developed an InP photodiode (PD) module integrated with an InP HBT preamplifier IC by using an Au stud bump. Theoretical analysis shows that the deviation of the group delay linearly increases in the inductance between the PD and IC. The flip-chip bonding based on the Au stud bump effectively reduces the inductance without sacrificing the individual device performance and reliability. Experimental results show that this technique is suitable for the receiver modules designed for applications with a bandwidth greater than 40 Gb/s

Input-Power and Polarization Insensitive All-Optical Wavelength Converter With Monolithically Integrated Monitor PD and Gain-Controlled SOA

This paper presents a polarization-insensitive semiconductor optical amplifier Mach-Zehnder Interferometer (SOA-MZI) wavelength converter with a wide dynamic range. Direct detection of the wavelength-converted output signal power and feedback control of the signal power input to the SOA-MZI are proposed and are confirmed to be able to reduce the variation with input signal power and polarization. The gain-controlled SOA (GC-SOA) and monitor PD used to implement the feedback control are monolithically integrated into the SOA-MZI wavelength converter. A dynamic range of over 8 dB is obtained for TE and TM polarized input signals NRZ modulated at 43 Gb/s under feedback control, 7 dB better than with no feedback.

Recent Advances in AlInsAs Avalanche Photodiodes

We present practical planar AlInAs APDs, which have large gain-bandwidth products, low noise, and high reliability. The APD receivers had a sensitivity of-28.6 dBm at 10 Gb/s and -37.0 dBm at 2.5 Gb/s.