Photoluminescence and Stability of Sputtered SiO_x Layers

Abstract

Silicon (Si) is the most important semiconductor material used in photovoltaic, microelectronic, and photonic devices. It is an ideal platform for monolithic integrated optoelectronic systems because it is nontoxic and inexpensive compared to the widely used III-V semiconductors. [1][2][3] However, Si was considered to be an unsuitable material for effective light generation. Its indirect bandgap stipulates weak light emission resulting from optical or electrical excitation. In 1981, quantum confinement was observed in silicon nanocrystals. [4,5] This effect was interrelated with an energy shift of optical absorption. Furthermore, light emission from Si nanocrystals (SiNCs) and porous Si was achieved. [4] Subsequently, SiNCs have drawn significant attention. As a result of the Heisenberg principle, the electron momentum distribution becomes broadened when the particle size decreases to a nanometer scale, thus providing a way for quasi-direct electronic transitions. It results in effective light generation in SiNCs via photoluminescence (PL). [6] The recombination of electrons and holes in SiNCs causes a bright PL signal at room temperature. [7] Changing the size of nanocrystals allows tuning the energy of the PL maximum. [4,8] Among the parameters affecting light emission from SiNCs in SiO x layers are the following: the impact of oxygen and chemical degradation in the ambient atmosphere, defects in the SiO x layers, substrate effects. [9][10][11] In addition, light emission may originate also from the substrate by laser-induced nonbridging oxygen hole centers (NBOHCs). [12] Achievement of efficient and controllable light emission in SiNCs would drastically enhance the development and use of Si-based optoelectronic devices due to their compatibility with mature Si-based electrical circuits.Various methods have been proposed so far to produce SiNCs embedded in different layers, such as plasma-enhanced chemical vapor deposition (PECVD), [13][14][15] electron beam (e-beam) evaporation, [16,17] ion implantation, [18,19] and sputtering. [20][21][22] Depending on the material and plasma settings, sputtering can provide homogeneous amorphous or crystalline layers with settable density. Therefore, it is also widely used in the fabrication of semiconductor and optical coatings on an industrial scale. SiNCs can form in amorphous Si-containing, e.g., SiO x , layers using annealing, which can be conductive or radiative thermal ones. It is known that