Graduate School of Engineering
Department of Materials Science

Materials science and technology as a basis for device realization:semiconductor processing for perfect crystals

Electronic and optical device performances are strongly dependent on the crystal perfection. Our research goal is focused on the realization to bring out materials nature and to create novel electronic and optical functions using nanometer or even atomic scale device fabrication processing. We investigate the interplay between crystallinity (point defect and nonstoichiometry etc.) and device characteristics. These devices are useful for information, medicine, environment and energy technologies.

Current Topics for information technologies(IT)

• THz transistor
  In order to realize high speed transistor operating with THz frequency, it is essential for semiconductor devices to be minitualized down to few 10nm or less. We are studying electron transport mechanism in such ultra small devices and Molecular Layer Epitaxy (MLE) technology as a fundamental process for nano-structure device fabrication.
• Semiconductor Raman laser/amplifier
  Semiconductor Raman laser and amplifier are realized by means of terahertz lattice vibration in semiconductors. These devices are promising devices for light frequency selection in terahertz bandwidth optical communications as well as wave length division multiplexing (WDM) optical communications.
• Optoelectronics materials
  We investigate the deviation from stoichiometry and related defects in compound semiconductors. Our main tool for defect recognition is the photocapacitance method. The effects to control stoichiometry of crystal growth have been observed such as the growth of almost dislocation-free GaP, GaAs and InP.

Current Topics for applications to medicine

• Frequency-Tunable High-Power Terahertz wave Generation System
  Many vibrations of bio-molecule exist in terahertz(THz) region. THz-wave irradiating with a selective frequency can excite specified biological molecule. We are developing Frequency-tunable high-power THz wave generation system based on the lattice vibration and exploring applications to medicine.
• Tunnett diode
  Terahertz frequencies operation of electron devices can be achieved with electron transport free of interaction with phonons, i.e., with ballistic or direct tunneling electron transport in semiconductors. One of the promising devices for THz operation is the tunnel injection transit time effect diode(TUNNETT). We have realized THz-wave generation in continuous-wave mode using the TUNNETT diode.
• middle-far infrared laser diode and CCD detector
  We are developing middle-far infrared laser diode(LD) and CCD detector, which have the promising application to medical lasers and gas sensors. We are realizing the infrared LD and CCD detector using PbTe crystal systems with stoichiometry control technology.

Current Topics for environment and energy technologies

• Static Induction Transistor (SIT)
  We are developing power devices(SIT etc.) essential to environment and energy technologies. The power devices can be operated with high power and high efficiency. In order to realize true high performance, control and evaluation of point defects are essential in power devices. This is the basis for defect enegineering technology.