Takuya Maruizumi

Interface structures generated by negative-bias temperature instability in Si/SiO2 and Si/SiOxNy interfaces

We used a density functional method to investigate the mechanism of negative-bias temperature instability (NBTI) and resultant structural changes of Si/SiO2 and Si/SiOxNy interfaces. The reaction energies for the water- and hydrogen-originated instabilities of several interface defects show that water-originated reactions of oxygen and nitrogen vacancies occur most easily. The larger instability of the Si/SiOxNy interface, compared with the Si/SiO2 interface, can be understood in terms of the difference in reaction energies. According to the calculated nitrogen 1s core-level shifts of the nitrogen atoms at the Si/SiOxNy interface, it is possible to identify a NBTI-generated structure at the Si/SiOxNy interface by x-ray photoelectron spectroscopy.We used a density functional method to investigate the mechanism of negative-bias temperature instability (NBTI) and resultant structural changes of Si/SiO2 and Si/SiOxNy interfaces. The reaction energies for the water- and hydrogen-originated instabilities of several interface defects show that water-originated reactions of oxygen and nitrogen vacancies occur most easily. The larger instability of the Si/SiOxNy interface, compared with the Si/SiO2 interface, can be understood in terms of the difference in reaction energies. According to the calculated nitrogen 1s core-level shifts of the nitrogen atoms at the Si/SiOxNy interface, it is possible to identify a NBTI-generated structure at the Si/SiOxNy interface by x-ray photoelectron spectroscopy.

Room-temperature electroluminescence from Si microdisks with Ge quantum dots

A current-injected silicon-based light-emitting device was fabricated on silicon-on-insulator (SOI) by embedding Ge self-assembled quantum dots into a silicon microdisk resonator with p-i-n junction for current-injection. Room-temperature resonant electroluminescence (EL) from Ge self-assembled quantum dots in the microdisk was successfully observed under current injection, and observed EL peaks corresponding to the whispering gallery modes (WGMs) supported by the microdisk resonator were well identified by means of numerical simulations.

Activated boron and its concentration profiles in heavily doped Si studied by soft x-ray photoelectron spectroscopy and Hall measurements

The chemical bonding states of boron (B) in shallow P+/N junctions on Si substrates were studied by soft x-ray photoelectron spectroscopy (SXPES). This study revealed three chemical bonding states of B embedded in bulk Si. The concentration profiles of B were successfully determined by combining SXPES with step-by-step etching of Si substrates. The concentration profiles of B thus determined were in good agreement with those determined by secondary ion mass spectroscopy. The concentration profiles of holes were also determined by combining Hall measurements with the step-by-step etching of Si substrates. The concentration profiles of B having the lowest binding energy were found to agree well with the concentration profiles of holes. Therefore, B with the lowest binding energy can be assigned as activated B and those having the middle and highest binding energies can be attributed to deactivated B having chemical bonding states different from that of activated B.

Silicon-Based Light-Emitting Devices Based on Ge Self-Assembled Quantum Dots Embedded in Optical Cavities

Highly efficient light-emitting devices operating in 1.3-1.6 μm wavelength range are realized by combining optical cavities and Ge self-assembled quantum dots (QDs) grown on SOI wafers by molecular beam epitaxy (MBE). Different types of optical cavities, including photonic crystal (PhC) nanocavities, microdisks, and microrings, are fabricated to enhance the light emission efficiency at room temperature. Sharp resonant peaks with Q-factor on the order of 103 are observed in the micro-photoluminescence (μPL) spectrum. Through numerical simulation, these peaks are well identified as the corresponding cavity modes. The emission performances of these devices are also investigated by performing pumping-power- and geometric-parameter-dependent μPL measurements. The resonant wavelength, Q-factor, and emission intensity can be easily manipulated by these parameters.

Silicon-based current-injected light emitting diodes with Ge self-assembled quantum dots embedded in photonic crystal nanocavities

Room temperature light emission from Ge self-assembled quantum dots (QDs) embedded in L3-type photonic crystal (PhC) nanocavity is successfully demonstrated under current injection through a lateral PIN diode structure. The Ge QDs are grown on silicon-on-insulator (SOI) wafer by solid-source molecular beam epitaxy (SS-MBE), and the PIN diode is fabricated by selective ion implantation around the PhC cavity. Under an injected current larger than 0.5 mA, strong resonant electroluminescence (EL) around 1.3-1.5 μm wavelength corresponding to the PhC cavity modes is observed. A sharp peak with a quality factor up to 260 is obtained in the EL spectrum. These results show a possible way to realize practical silicon-based light emitting devices.

INCORPORATION OF N INTO SI/SIO2 INTERFACES : MOLECULAR ORBITAL CALCULATIONS TO EVALUATE INTERFACE STRAIN AND HEAT OF REACTION

The determining factor for the accumulation of N at a Si/SiO2 interface during oxynitridation of the interface was investigated using a quantum-chemical method. Both mechanical and chemical factors (the interface strains and the heats of reaction of the oxynitridation) were considered. Though a slight relaxation of interface strain occurs when the interface has a certain type of oxygen-vacancy defect, we found the N incorporation does not relax the interface strain in most cases. The exothermicity and endothermicity of the oxynitridation reaction in the Si and SiO2 films, respectively, are the primary cause of the accumulation of N at the interface.

Enhanced 1524-nm Emission From Ge Quantum Dots in a Modified Photonic Crystal L3 Cavity

Light emitters based on Ge quantum dots embedded in modified photonic crystal three defect-long (L3) cavities are fabricated and characterized. Several sharp resonant luminescence peaks dominate the photoluminescence (PL) spectrum at room temperature. The strongest resonant luminescence peak is obtained at 1524 nm. The enhancement factor is 110, and the corresponding Purcell factor is estimated to be 6.7. The large enhancement is due to high Purcell factor and high collection efficiency of modified L3 cavity verified by far-field patterns. The intrinsic Q factor measured from crossed-polarized resonant scattering is much higher than the Q factor measured from PL, indicating that the Q factors measured from PL are inaccurate due to free-carrier absorption of the photogenerated carriers.

Subnitride and valence band offset at Si3N4∕Si interface formed using nitrogen-hydrogen radicals

The authors measured soft x-ray-excited angle-resolved photoemission from Si 2p, N 1s, and O 1s core levels, and valence band for nitride films formed on Si(100), Si(111), and Si(110) using nitrogen-hydrogen radicals with the same probing depth. The Si3N4∕Si interfaces formed exhibited an almost abrupt compositional transition. Furthermore, the crystal orientation of Si substrate affects the total areal density of subnitrides but not the valence band offset at the Si3N4∕Si interface.

Interface structures generated by negative-bias temperature instability in Si/SiO/sub 2/ and Si/SiO/sub x/N/sub y/ interfaces

Accordingly, we investigated possible NBTI mechanisms and resultant structural changes at Si/SiO/sub 2/ and Si/SiO/sub x/N/sub y/ interfaces. To determine if it is possible to identify a NBTI-generated structure through XPS of the interface, the N 1s core-level shifts of various structures at the Si/SiO/sub x/N/sub y/ interface were also evaluated. We further considered the important role of hydrogen to localize the hole trapped in the interface.

Angle-resolved photoelectron spectroscopy on gate insulators.

Abstract This work reviews the study of the chemical composition and the chemical structure of ultrathin oxynitride films using angle-resolved photoelectron spectroscopy. The nearest and the second nearest neighbors of a nitrogen atom in oxynitride films were determined from the deconvolution of N 1s spectra. It was found by applying maximum entropy concept to the angle resolved Si 2p and N 1s photoelectron spectra that the distribution of nitrogen atoms and their bonding configurations in oxynitride films formed by the plasma nitridation is quite different from those in oxynitride films formed by the interface nitridation.