Creation of the synthetic Rashba field in a Si channel of Si spin MOSFET is introduced and discussed. The Rashba field is attributed to the local electric field at the Si/SiO₂ interface and is tuneable by a gate electric field. An effective magnetic field due to the Rashba field gives rise to spin lifetime anisotropy in a Si channel, which is detected by the oblique Hanle effect. It is also found that the Rashba field is built-in even at the gate voltage of 0 V. The magnitude of the spin splitting energy is estimated to be 0.6 μeV, which is comparable to that in strained GaAs.

Metallic delafossites ABO₂ (PdCoO₂, PdCrO₂, PdRhO₂, and PtCoO₂) are among the most conducting metals, having the electrical conductivity comparable with that of elemental Au. This remarkable electrical conductivity resides in the quasi-two dimensional layered crystal structure consisting of alternating A⁺ and [BO₂]^- layers. In this short article, I will introduce our recent research on thin-film growth of metallic delafossites. I will also briefly overview the physical properties of metallic delafossites, focusing on the surface/interface phenomena arising from their polar layered crystal structure.

Niobium nitride (NbN) is a superconducting material used in single photon detectors and quantum bits. Because NbN is lattice-matched to the wide-gap semiconductor AlN, it is possible to integrate the functions of nitride semiconductors and superconductors via epitaxial growth. However, the basic properties of NbN thin films epitaxially grown on nitride semiconductors are still unclear. In this article, we show the structural and electrical properties of NbN thin films grown on AlN by sputtering. We also discuss the mechanism that the difference in crystal structure between AlN and NbN leads to the formation of NbN twins.

In this article, we review our recent studies on excitonic optical properties of deep-UV luminescent AlGaN. The characteristics of optically pumped stimulated emission from AlGaN-based UV-C multiple quantum wells were studied as a function of temperature. The change in the mechanism of optical gain formation from excitonic transition to degenerated electron-hole plasma was observed with increasing temperature. Excitonic stimulated emission was observed up to 450 K, indicating a low threshold carrier density and high thermal stability at room temperature. Furthermore, lasing spectra with fine structures due to the longitudinal cavity mode were clearly observed, confirming excitonic lasing at room temperature.

In the field of quantum electron optics, where quantum optics experiments are performed using propagating electrons, quantum states of finite-size wave packets of single electrons should be manipulated. Among various types of wave packets, a single electron confined in a moving potential of a surface acoustic wave (SAW) serves as the smallest wave packet. In this article, we discuss transfer of single electrons by SAWs and control of the SAW-driven quantum transport.

Semiconductor devices, which have become indispensable in our daily lives, operate by the movement of charge carriers (electrons and holes) in real space and energy spaces. We are developing a photoelectron emission microscope (PEEM) with femtosecond laser pulses to evaluate semiconductor materials and for operands observation. In addition to spatial resolution using a PEEM and temporal resolution using laser pulses, energy resolution is accompanied by continuously varying the photon energy of the laser pulses in the ultraviolet region. As a result, dynamics of conducting electrons are imaged with a high signal-to-noise ratio. In this paper, we describe the details of the system, and introduce two results on advanced materials.

The DLTS (deep-level transient spectroscopy) is recognized as one of various methods to evaluate defects in semiconductors. It uses the depletion-layer capacitance transients caused by the change of charge states of defects in the depletion region of devices due to the bias pulses. This enables to observe electrically active defects which directly affect the device performance. In this fundamental lecture, the temperature-scan DLTS is presented as an introduction and basis to the DLTS. The interpretation of DLTS signals is given together with the experimental procedure to perform DLTS measurements.