Eiji Yagyu

AlGaN Channel HEMT With Extremely High Breakdown Voltage

Enhanced performance of RF power modules is required in a next-generation information society. To satisfy these requirements, we designed a novel high-electron mobility transistor (HEMT) structure employing wider bandgap AlGaN for a channel layer, which we called AlGaN channel HEMT, and investigated it. The wider bandgap is more effective for higher voltage operation of HEMTs and contributes to the increase of output power in RF power modules. As a result, fabricated AlGaN channel HEMTs had much higher breakdown voltages than those of conventional GaN channel HEMTs with good pinchoff operation and sufficiently high drain current density without noticeable current collapse. Furthermore, specific on-state resistances of fabricated AlGaN channel HEMTs were competitive with the best values of reported GaN- and SiC-based devices with similar breakdown voltages. These results indicate that the proposed AlGaN channel HEMTs are very promising not only for an information-communication society but also in the power electronics field.

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.

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

Design and Characteristics of Guardring-Free Planar AlInAs Avalanche Photodiodes

This paper reports a guardring-free planar AlInAs avalanche photodiode (APD) for optical fiber communications. AlInAs APDs can achieve a larger gain-bandwidth product (GBP) with lower excess noise than commercial InP APDs, and the guardring-free planar structure enables these superior AlInAs APDs to have both a low dark current and high reliability for practical use. We present the structure, fabrication, designs, APD characteristics, and receiver sensitivity, systematically. The guardring-free planar structure and its peculiarities are described, and we show APD designs for 2.5-Gb/s and 10-Gb/s applications and their characteristics. A 0.2-mum -thick AlInAs multiplication layer achieves a GBP of 120 GHz and an excess noise factor of 2.9 at a multiplication factor of 10. Their dark currents are less than 20 nA and their lifetime is evaluated to be 25 million hours at 85degC. Lastly, we demonstrate that the guardring-free planar AlInAs APDs with a transimpedance amplifier achieve the remarkable sensitivity of -37.0 dBm at a bit error rate of 10-10 for 2.5-Gb/s signals and of -29.9 dBm at a bit error rate of 10-12 for 10-Gb/s signals. This performance indicates that the guardring-free planar AlInAs APDs have made great advances against commercial InP APDs and other AlInAs APDs.

Analysis of Single-Photon-Detection Characteristics of GaInAs/InP Avalanche Photodiodes

An effective method to analyze the origin of primary dark counts is presented for single-photon-detection avalanche photodiodes (APDs) operated in the gated Geiger modes. It is revealed that a band-to-band tunneling model reproduces the experimental data very well for GaInAs/InP single-photon-detection APDs, while a phonon-assisted tunneling model fails. Therefore, we concluded that primary dark counts are dominated by the band-to-band tunneling for the GaInAs/InP single-photon-detection APDs. Then, we calculate the dark count probability and the detection efficiency by modeling the band-to-band tunneling. It is found that the ratio of the dark count probability to the detection efficiency is reduced by decreasing the impurity concentration of the multiplication region and of the p-type window.

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.

Guardring-Free Planar AlInAs Avalanche Photodiodes for 2.5-Gb/s Receivers With High Sensitivity

We demonstrate a practical 2.5-Gb/s AlInAs avalanche photodiode (APD) and an AlInAs APD-based optical receiver with high sensitivity. The AlInAs APD has a simple guardring-free planar structure with high reliability. In addition to the inherent low excess noise of AlInAs, their simplicity and high yields are great advantages in production, even when contrasted with the planar InP APDs now on the market. The guardring-free AlInAs APDs achieve larger gain-bandwidth (GB) products and lower excess noise, with a maximum 3-dB bandwidth of 6.0 GHz and a GB product of typically 80 GHz, and have equal performance with InP APDs, which have a responsivity of 1.0 A/W and a multiplying dark current of 2.2 nA. An AlInAs APD-based 2.5-Gb/s optical receiver with a SiGe transimpedance amplifier has a sensitivity of -37.0 dBm at a bit-error rate of 10-10

Highly reliable guardring-free InAlAs avalanche photodiodes

The InAlAs avalanche photodiodes that employ a guardring-free structure demonstrate record high reliability of over 10000 hours at a high temperature of 200degC with no degradation in the surfaced pn-junction.