Microtwinning in microcrystalline silicon and its effect on grain-size measurements

Abstract

Microcrystalline silicon grown by plasma-enhanced chemical vapor deposition consists of a phase mixture of amorphous silicon and submicrometer sized columnar crystalline silicon grains. These grains do not exhibit perfect translational symmetry but show a high density of microtwins, evidenced by structural investigations by use of transmission electron microscopy and x-ray diffraction. The high twin fault density of typically every tenth ͕111͖ bilayer leads to anisotropic size broadening effects for Bragg reflection peaks. This anisotropic behavior of size broadening interferes with grain-size and strain measurements from x-ray diffractograms. Experimentally measured apparent grain sizes are up to a few ten nanometers and are subject to significant scatter due to the effect of microtwinning. Numerical modeling of the shape of Bragg reflection peaks is presented for the two characteristic modifications of microtwinning, i.e., lamellar and random twinning, to assess quantitatively the effect of microtwinning on size broadening and grain-size measurements from Bragg reflection width.

Mechanism insight into the effect of I/P buffer layer on the performance of NIP-type hydrogenated microcrystalline silicon solar cells

“…This thickness is supported by the phase diagrams measured using real-time spectroscopic ellipsometry by Collins et al 25 A Gaussian dangling-bond distribution model with a standard deviation of 0.2 eV was adopted to describe the broad distribution of dangling bonds. 26,27 The overall material parameters employed in the simulation is tabulated in the Appendix (see Table II). Fig.…”

Characterization of room temperature recrystallization kinetics in electroplated copper thin films with concurrent x-ray diffraction and electrical resistivity measurements

“…14 For samples with coherently diffracting regions (i.e., the regions between twins and/or regions containing no stacking faults or dislocations) larger than approximately 100 nm, these broadening contributions are much smaller than the contributions due to coherent domain size and strain and can be neglected. 14,31 For a polycrystalline thin film (Figure 2(a)), the measured intensity is the sum of the diffracted intensities from all "M" grains satisfying Bragg's law…”

Electrical detection of electron-spin-echo envelope modulations in thin-film silicon solar cells

“…The crystalline columns present in μc-Si:H consist of grains of perfect crystal quality separated by grain boundaries. 40 In contrast to the amorphous matrix, the crystalline grains are expected to contain only a small quantity of H. The absence of 1 H-ESEEM in the case of CE centers is therefore a strong indication that these centers are not located in the amorphous phase or at the boundary between crystalline and amorphous phases since the amorphous phase contains H in large concentrations. This conclusion excludes models b and c where CE centers are attributed to interface defects or electrons confined to an inversion layer at the boundary of amorphous and crystalline phases, since in the case of a planar interface the ω I ( 1 H) and 2ω I ( 1 H) peak intensities should indicate a hydrogen density of about half the hydrogen content in the amorphous phase.…”

“…However, in μc-Si:H, dislocations or point defects are absent in crystalline columns and grains. 40 The only important lattice distortions or crystal defects in crystalline grains are coherent twin boundaries with a high density (twin fault probability λ = 0.1). 40 Theoretical studies of the atomic and electronic structure of silicon twin grain boundaries revealed that they induce shallow localized electronic states.…”

“…40 The only important lattice distortions or crystal defects in crystalline grains are coherent twin boundaries with a high density (twin fault probability λ = 0.1). 40 Theoretical studies of the atomic and electronic structure of silicon twin grain boundaries revealed that they induce shallow localized electronic states. 41,42 The latter can be rationalized qualitatively by considering that coherent twin grain boundaries conserve the tetrahedral coordination of the lattice while the bond lengths and angles of Si atoms at the grain boundary are disturbed.…”