Nobuyuki Fujimura

Evaluation of valence band top and electron affinity of SiO2 and Si-based semiconductors using X-ray photoelectron spectroscopy

An evaluation method for the energy level of the valence band (VB) top from the vacuum level (VL) for metals, dielectrics, and semiconductors from the results of X-ray photoelectron spectroscopy (XPS) is presented for the accurate determination of the energy band diagram for materials of interest. In this method, the VB top can be determined by the energy difference between the onset of VB signals and the cut-off energy for secondary photoelectrons by considering the X-ray excitation energy (hν). The energy level of the VB top for three kinds of Si-based materials (H-terminated Si, wet-cleaned 4H-SiC, and thermally grown SiO2) has been investigated by XPS under monochromatized Al Kα radiation (hν = 1486.6 eV). We have also demonstrated the determination of the electron affinity for the samples by this measurement technique in combination with the measured and reported energy bandgaps (E g).

Electroluminescence of superatom-like Ge-core/Si-shell quantum dots by alternate field-effect-induced carrier injection

We have fabricated high-density superatom-like Si–Ge-based quantum dots (Si-QDs with Ge core) and studied their luminescence properties. Electroluminescence was observed from the Si-QDs with Ge core at room temperature in the near-infrared region by the application of square-wave pulsed bias of ±1 V at 500 kHz, which was attributed to radiative recombination between quantized states in the Ge core with deep potential well for holes caused by field-effect-induced alternate electron/hole injection from the substrate. The results lead to the development of Si-based light-emitting devices that are highly compatible with ultra-large-scale integration processing, which was found difficult to realize in silicon photonics.

Photoemission study on electrical dipole at SiO2/Si and HfO2/SiO2 interfaces

Electrical dipole at SiO2/Si and HfO2/SiO2 interfaces have been investigated by X-ray photoelectron spectroscopy (XPS) under monochromatized Al Kα radiation. From the analysis of the cut-off energy for secondary photoelectrons measured at each thinning step of a dielectric layer by wet-chemical etching, an abrupt potential change caused by electrical dipole at SiO2/Si and HfO2/SiO2 interfaces has been clearly detected. Al-gate MOS capacitors with thermally-grown SiO2 and a HfO2/SiO2 dielectric stack were fabricated to evaluate the Al work function from the flat band voltage shift of capacitance–voltage (C–V) characteristics. Comparing the results of XPS and C–V measurements, we have verified that electrical dipole formed at the interface can be directly measured by photoemission measurements.