Shimomura Kazuhiko

Emission wavelength control of InAs QDs using MOVPE have been studied. Emission wavelength in each arrayed waveguides was controlled by selective area growth of MOVPE using SiO2 mask. Heights of QDs were controlled by using double-capping method, and emission wavelength was controlled by changing the composition of GaInAs buffer layer beneath the QDs. By using these methods, broadband InAs QDs LED, more than 600nm bandwidth, and flat-top spectrum have been obtained.

We have demonstrated (Ga)InAs/InP QD arrayed waveguide LED on directly bonded InP/Si substrate. Electroluminescence signal from the LED has been achieved and comparable peak wavelength was observed from both the sample and reference grown on InP substrate. These results are promising in terms of integration of communication wavelength light source on InP/Si substrate.

A nanowire-CMOS heterogeneously integrated circuit is demonstrated. The circuit consists of a voltage divider and a delta-sigma modulator (DSM); InAs nanowires are used in the voltage divider. InAs nanowires are deposited on a CMOS substrate by using Field-Assisted Self-Assembly (FASA) process based on dielectrophoresis. The DSM successfully converts the voltage across the nanowire into density-modulated digital pulses. The present result suggests that variations in the nanowire resistance caused, for example, by chemical absorption on the nanowire surface can be sensed and converted into the digital output. Furthermore, nanowire deposition is electrically monitored by measuring time variation of the current during the FASA.

Integrating III-V materials which enables high-speed computer with large-capacity on Si has been required. Therefore, we have fabricated InP/Si substrate employing wafer direct bonding and wet-etching. Then growth of GaInAs/InP MQW structure has been realized on the substrate using MOVPE. The same work has also been demonstrated on SiO_2-Si and Glass substrate. Furthermore, selective MOVPE growth of GaInAs/InP MQW structure has been done on the InP/Si substrate. Our work is of importance in terms of integration of several functional optical devices on heterogeneous substrate.

Field-assisted self-assembly process (FASA) of InAs and InAs/InP core-shell nanowires onto a Si substrate has been investigated. The dependence of the FASA yield on the frequency of the AC voltage applied between the FASA electrodes is examined. Furthermore, nanowires are deposited onto a MOS substrate to obtain an nMOS inverter. It is confirmed that the inverter operates properly.

A GaInAs/InP MQW-based wavelength demultiplexer composed of a waveguide array in which refractive index varies across the array yielded successful results. Since optical path length differences between waveguides in the array are achieved through refractive-index differences controlled by SiO2 mask design in selective metal-organic vapor phase epitaxy MOVPE, straight waveguide grating is possible with reducing optical propagation losses. A straight waveguide array device with a 1.4 % refractive-index difference was fabricated. The fabrication of a preliminary wavelength demultiplexer was also achieved, obtaining a wavelength separation with around 25-nm spacing and FSR of approximately 100 nm. Moreover, an optical deflector was investigated and achieved primitive deflection at 1460- and 1490-nm incident wavelengths.

We have measured the gate length dependence of the optical response characteristics in optically controlled MOSFET. By changing the pattern of optical absorption region, the leakage current was reduced remarkably, and we obtained almost same current-voltage characteristics in metal gate MOSFET. We have measured the optical response characteristics, such as modulation current, on-off ratio and responsivity in optically controlled MOSFET, and we obtained the high current modulation and responsivity by reducing the gate length of MOSFET region.