Structure of Microcrystalline Si(Ge) Produced by Plasma Chemical Reaction

Abstract

Plasma chemical reactions produce microcrystalline states of silicon and germanium (μc-Si and μc-Ge), Atomic and morphological structures of μc-Si grain and film are investigated by means of electron microscopy, vibrational spectroscopy, etc.
The grain of, μc-Si produced by rf sputtering of a Si dis k target in pure H₂ atmosphere (Table 1) consists of a single crystal of Si (diamond structure) in irregular shape of dimensions 5∼50 nm (Fig.1 and Fig.2). The surface of μc-Si grain is covered with hydrogen atoms covalently bonding with Si atoms (Table 3). Content of hydrogen in, uc-Si film has been measured to be about 30 atom%.
A film of μc-Si shows colum nar structure composed of the aggregate of μc-Si grains, when the film is sufficiently thick. The columnar structure develops with the growth of μc-Si film (Fig.3 b). The surface morphological observation of the film by SEM shows roun d grains in shape with dimension of several hundred nm (Fig.3 a).
Crystalline nature of μc-Ge is summarized in Table 2.
Optical absorption spectra of μc-Si and, uc-Ge resemble those in the single crystal Counter parts (Fig.6 and Fig.8). Photoluminescence spectra of μc-Si film show also crystalline nature rather than amorphous one (Fig.7). There are many defects including ESR centers of ∼10¹⁸ spin/cm3 in μc-Si grain and film.
Infrared absorption bands in Si-H stretc hing vibration region- are composed of sever al fine peaks (Fig.4). Assignment of these peaks is discussed in terms of electron negativities of adjacent substituted groups, symmetric and anti-symmetric vibrations of SiH₂ group, and SiH structures located closely each other on ac-Si grain surfaces.
A morphological model for μc-Si film produced by rf glow discharge decompositio n of SiH₄ i s discussed from the photoluminescence properties and lower hydrogen content in that film.