Room Temperature Light Emission from Superatom-like Ge-Core/Si-Shell Quantum Dots.

We have demonstrated the high-density formation of super-atom-like Si quantum dots with Ge-core on ultrathin SiO2 with control of high-selective chemical-vapor deposition and applied them to an active layer of light-emitting diodes (LEDs). Through luminescence measurements, we have reported characteristics carrier confinement and recombination properties in the Ge-core, reflecting the type II energy band discontinuity between the Si-clad and Ge-core. Additionally, under forward bias conditions over a threshold bias for LEDs, electroluminescence becomes observable at room temperature in the near-infrared region and is attributed to radiative recombination between quantized states in the Ge-core with a deep potential well for holes caused by electron/hole simultaneous injection from the gate and substrate, respectively. The results will lead to the development of Si-based light-emitting devices that are highly compatible with Si-ultra-large-scale integration processing, which has been believed to have extreme difficulty in realizing silicon photonics.

Ultrathin silicon oxynitride layer on GaN for dangling-bond-free GaN/insulator interface.

Despite the scientific and technological importance of removing interface dangling bonds, even an ideal model of a dangling-bond-free interface between GaN and an insulator has not been known. The formation of an atomically thin ordered buffer layer between crystalline GaN and amorphous SiO2 would be a key to synthesize a dangling-bond-free GaN/SiO2 interface. Here, we predict that a silicon oxynitride (Si4O5N3) layer can epitaxially grow on a GaN(0001) surface without creating dangling bonds at the interface. Our ab initio calculations show that the GaN/Si4O5N3 structure is more stable than silicon-oxide-terminated GaN(0001) surfaces. The electronic properties of the GaN/Si4O5N3 structure can be tuned by modifying the chemical components near the interface. We also propose a possible approach to experimentally synthesize the GaN/Si4O5N3 structure.

Growth and applications of GeSn-related group-IV semiconductor materials.

We review the technology of Ge1-x Sn x -related group-IV semiconductor materials for developing Si-based nanoelectronics. Ge1-x Sn x -related materials provide novel engineering of the crystal growth, strain structure, and energy band alignment for realising various applications not only in electronics, but also in optoelectronics. We introduce our recent achievements in the crystal growth of Ge1-x Sn x -related material thin films and the studies of the electronic properties of thin films, metals/Ge1-x Sn x , and insulators/Ge1-x Sn x interfaces. We also review recent studies related to the crystal growth, energy band engineering, and device applications of Ge1-x Sn x -related materials, as well as the reported performances of electronic devices using Ge1-x Sn x related materials.

Ge-rich SiGe-on-insulator for waveguide optical modulator application fabricated by Ge condensation and SiGe regrowth.

We have numerically analyzed plasma dispersion effect in a Ge-rich SiGe layer for optical modulator applications. Since strain induces reduction in effective masses of electron and hole, we expect enhanced plasma dispersion effect in a strained Ge-rich SiGe layer. The plasma dispersion effects of Si(0.15)Ge(0.85) on Si(0.2)Ge(0.8) for hole and electron are expected to be approximately 3.0 and 1.5 times larger than those of Si. To realize Ge-rich SiGe-based waveguide optical modulators, we have also investigated the fabrication procedure of SiGe-on-insulator (SGOI) wafers. We have successfully fabricated Ge-rich SGOI wafers without any thick SiGe buffer layers by using Ge condensation in conjunction with the SiGe regrowth technique. We have evaluated the SGOI by Raman spectroscopy, atomic force microscopy (AFM), reflected high energy electron diffraction (RHEED) and transmission electron microscopy (TEM). Ge-rich SiGe waveguides have been fabricated on the SGOI wafer. The propagation loss was found to be approximately 13 dB/mm, which can be reduced to be below 2 dB/mm by optimizing the Ge condensation process. We expect that strained SiGe grown on the fabricated SGOI exhibits more than 2.3 times higher plasma dispersion than Si in case of a carrier injection type, suitable for high-performance waveguide optical modulators.

Initial Processes of Atomic Layer Deposition of Al2O3 on InGaAs: Interface Formation Mechanisms and Impact on Metal-Insulator-Semiconductor Device Performance.

Interface-formation processes in atomic layer deposition (ALD) of Al2O3 on InGaAs surfaces were investigated using on-line Auger electron spectroscopy. Al2O3 ALD was carried out by repeating a cycle of Al(CH3)3 (trimethylaluminum, TMA) adsorption and oxidation by H2O. The first two ALD cycles increased the Al KLL signal, whereas they did not increase the O KLL signal. Al2O3 bulk-film growth started from the third cycle. These observations indicated that the Al2O3/InGaAs interface was formed by reduction of the surface oxides with TMA. In order to investigate the effect of surface-oxide reduction on metal-insulator-semiconductor (MIS) properties, capacitors and field-effect transistors (FETs) were fabricated by changing the TMA dosage during the interface formation stage. The frequency dispersion of the capacitance-voltage characteristics was reduced by employing a high TMA dosage. The high TMA dosage, however, induced fixed negative charges at the MIS interface and degraded channel mobility.