M. Hirose

Control of self-assembling formation of nanometer silicon dots by low pressure chemical vapor deposition

Abstract The formation of nanometer-scale silicon dots on ultrathin SiO 2 layers has been studied by controlling the early stages of low-pressure chemical vapor deposition (LPCVD) of a monosilane gas. It has been suggested that the thermal dissociation of surface Si–O bonds plays a role in creation of nucleation sites on as-grown SiO 2 and that surface Si–OH bonds formed by a dilute HF treatment or pure water immersion act as nucleation sites during LPCVD. By spatially controlling OH-termination on the SiO 2 surface before LPCVD, the selective growth of Si dots has been demonstrated.

Quantum confinement effect in self-assembled, nanometer silicon dots

The first subband energy at the valence band of self-assembled silicon quantum dots grown by low-pressure chemical vapor deposition on ultrathin SiO2/Si substrates has been measured as an energy shift at the top of the valence band density of states by using high-resolution x-ray photoelectron spectroscopy. The systematic shift of the valence band maximum towards higher binding energy with decreasing the dot size is shown to be consistent with theoretical prediction. The charging effects of the silicon dots and the SiO2 layer by photoelectron emission during the measurements have been taken into account in determining the valence-band-edge energy.

Charging States of Si Quantum Dots as Detected by AFM/Kelvin Probe Technique

Hemispherical Si quantum dots have been self-assembled on thermally grown 3.2-nm-thick SiO2/p-Si(100) by low-pressure chemical vapor deposition of silane. The charging states of the Si quantum dots have been detected as surface potential changes by using an atomic force microscopy/Kelvin force probe method. From the relationship between the measured surface potential changes and the charging energy of a single dot, the number of electrons retained in a dot has been estimated to be one. Furthermore, it is found that electron extraction from neutral dots can be achieved to create a hole at each dot.

Luminescence from Thermally Oxidized Porous Silicon

Porous silicon produced by means of anodization in an HF-based solution has been oxidized in an N2+O2 gas mixture at 900 or 1000°C to realize the ideal passivation of a porous Si surface with thermally grown oxide instead of hydrogen termination. Visible photoluminescence at room temperature has been observed for porous Si whose surface is terminated by oxygen. It is shown that the luminescence from the porous silicon is extremely stable under Ar+ laser light (488 nm) irradiation even in air at room temperature. A possible mechanism for the visible light emission is discussed on the basis of the excitation intensity dependence of the luminescence.

Intense Visible Luminescence from Thermally-Oxidized Porous Silicon

Photoluminescence from porous silicon oxidized at 800 or 900°C in an N 2 +O 2 gas mixture has been investigated. The ideal passivation of the porous Si surface with thermally grown oxide results in stable, intense visible-light emission. The steady-state and time-resolved luminescence measured as functions of temperature and excitation power have indicated that a possible pathway for the light emission is the radiative recombination through localized states.

Wide-Gap Polysilane Produced by Plasma-Enhanced CVD at Cryogenic Temperatures

Polysilane thin films have been grown by the rf glow discharge decomposition of SiH 4 at substrate temperatures ranging from -84 to -110°C. The infrared absorption spectra have shown that polysilane chains (SiH 2 ) n are predominantly incorporated in the matrix together with SiH 3 which terminates the chain. Also, the infrared absorption band at 2120∼2140 cm -1 and a distinct Raman peak at ∼430 cm -1 indicates that fairly long chains (SiH 2 ) n with n>11 are produced. Polysilane prepared at -110°C has an optical bandgap of about 3.1 eV and exhibits a visible luminescence around 2.75 eV at 100 K.