YAMADA Laboratory
<Major Research Areas>Semiconductor Physics, Quantum Electron Transport, Spintronics, Micro-machine

Semiconductor Spintronics and
Micro-machine: Novel Fields of
Compound Semiconductor Research

Research activity

1MBE growth of high-quality 2-dimensional quantum structures of compound semiconductors

　　In order to study the mesoscopic and/or spin-related transport physics, we are carrying out the studies of epitaxial growth of highquality modulation doped hetero-structures by molecular beam epitaxy (MBE). We focus on the hetero-junction material systems such as GaAs/AlGaAs, InGaAs/InAlAs and InGaSb/InAlSb. Especially, in InGaAs/InAlAs two-dimensional electron gas (2DEG), highest electron mobility of 5x105cm2/Vsec and spin-orbit coupling constant of 35(x10-12eVm) were attained at low temperatures.

2Band structure analysis and spectroscopic study of low-dimensional electron systems in compound semiconductors

　　By utilizing the magneto-resistance, magneto-tunneling, and cyclotron resonance experiments at low temperatures, we are analyzing the sub-band structures of the 2-dimensional electron or hole gases confined in hetero-junctions and/or quantum wells. Especially, the effects of strain on the band structures and spinrelated phenomena are the major interests in our group. In Fig. 1, spin-orbit interaction in semiconductor hetero-junction is shown schematically. Also the electronic states in quantum wells, wires and dots are analyzed by using the spectroscopic methods with visible and infrared light.

3Fabrication of ultra-small structures and devices and study of their mesoscopic physics

　 　In addition to the standard nano-fabrication techniques such as ultra-violet and electron beam lithographies, we adopted the methods using focused-ion-beam and probe chip to fabricate semiconductor small structures and electronic devices with small ferromagnetic electrodes. We then study the novel transport physics which are expected to appear in those structures, and make efforts for the realization of spin-control devices and quantum functional devices. In Fig. 2, we show the model of spin-transistor. Devices for quantum computation are one of our research targets in future.

4Fabrication of micro-nano machines by utilizing the semiconductor lithography techniques

　 　By applying the various techniques for semiconductor small structure fabrications, we are developing the batch fabrication technologies to make various kinds of micro-nano mechanical components based on the compound semiconductors. Integration with usual semiconductor devices and hybridization with different material such as ceramics are studied to realize multi-functioned and/or intelligent small mechanical components such as cantilevers in atomic force microscopy (AFM). Figure 3 shows the hybrid cantilever made with GaAs and ceramics.

Equipment

molecular beam epitaxy equipment (fabrication of multi-layer structure of compound semiconductor), electron-beam lithography equipment (fabrication of small electronic devices and micro/nano machines), liquid Helium cryostat with super-conductive magnets (measurements of fundamental properties of the devices)

The main research achievements in the past five years

1. M. Akabori, K. Morimoto, W. Wei, H. Iwase, S. Yamada，Growth and magneto-transport characterization of double-doped InGaAs/InAlAs heterostructures with high Indium compositions，Proc. 30th Int. Conf. on the Physics of Semiconductors，P2-254，July 29, (2010).
2. T. K. Sasaki, H. Iwase, J. Wang, M. Akabori, S. Yamada，Spring characteristics of circular arc shaped 3D micro-cantilevers fabricated using III-V semiconductor strain-driven bending process，Proc. 30th Int. Conf. on the Physics of Semiconductors，P2-392，July 29, (2010).
3. S. Yamada, S. Nitta, H. Iwase, M. Akabori, Y. Imanaka, T. Takamasu,Magnetic field dependency of spin-splitting in InGaAs/InAlAs two-dimensional electron gas with strong Rashba spin-orbit coupling,The 19th Int. Conf. on the Application of High Magnetic Fields in Semiconductor Physics and Nanotechnology，ThP-19，Aug. 4 (2010).
4. Y. Imanaka, T. Takamasu, S. Nitta, S. Yamada，Cyclotron resonance of two-dimensional Rashba systems in InGaAs，The 19th Int. Conf. on the Application of High Magnetic Fields in Semiconductor Physics and Nanotechnology，ThP-18，Aug. 4, (2010).
5. S. Nitta, H. K. Choi and S. Yamada, "In-plane anisotropic transport in 2DEGs having a strong spin-orbit coupling in In[0.75]Ga[0.25]As/ In[0.75]Al[0.25]As hetero-junctions", 18th Int. Conf. Electronic Properties of Two-dimensional Systems, Physica E42, 984 (2010).