3.3 Lattice
43
(a)
c
c/4
4 1
4 2
c/2
(b)
c/2
2 1
glide
Fig. 3.12 a Schematic drawing of a 4 1 and 4 2 screw axis. b Schematic drawing of an axial glide reflection. The mirror
plane is shown with dashed outline. Opposite faces of the cube have opposite color. For comparison a 2 1 screw axis is
shown
(a)
(b)
(c)
Fig. 3.13 Transmission electron micrographs of polycrystalline silicon (poly-Si). a As-deposited material from lowpressure chemical vapor deposition (LPCVD) at about 620 ◦ C, grain size is about 30 nm. b After conventional processing
(annealing at 1150 ◦ C), average grain size is about 100 nm. c After annealing in HCl that provides enhanced point defect
injection (and thus increased possibility to form larger grains), average grain size is about 250 nm. Adapted from [196]
3.3.6 Polycrystalline Semiconductors
A polycrystalline material consists of crystal grains that are randomly oriented with respect to each
other. Between two grains a (large-angle) grain boundary (see also Sect. 4.4.3) exists. An important
parameter is the grain size and its distribution. It can be influenced via processing steps such as
annealing. Polycrystalline semiconductors are used in cheap, large-area applications such as solar
cells (e.g. polysilicon, CuInSe 2 ) or thin-film transistors (poly-Si) or as n-conducting contact material
in MOS diodes (poly-Si) as shown in Fig. 3.13 (see also Fig. 21.29). Polycrystalline material can be
fabricated from amorphous material using annealing procedures as discussed in Sect. 24.6.1 for silicon.
3.3.7 Amorphous Semiconductors
An amorphous material lacks the long-range order of the direct lattice. It is disordered on the atomic
scale. Historically, amorphous Se (a-Se) has been investigated first; since the 1950’s amorphous chalco-
43
(a)
c
c/4
4 1
4 2
c/2
(b)
c/2
2 1
glide
Fig. 3.12 a Schematic drawing of a 4 1 and 4 2 screw axis. b Schematic drawing of an axial glide reflection. The mirror
plane is shown with dashed outline. Opposite faces of the cube have opposite color. For comparison a 2 1 screw axis is
shown
(a)
(b)
(c)
Fig. 3.13 Transmission electron micrographs of polycrystalline silicon (poly-Si). a As-deposited material from lowpressure chemical vapor deposition (LPCVD) at about 620 ◦ C, grain size is about 30 nm. b After conventional processing
(annealing at 1150 ◦ C), average grain size is about 100 nm. c After annealing in HCl that provides enhanced point defect
injection (and thus increased possibility to form larger grains), average grain size is about 250 nm. Adapted from [196]
3.3.6 Polycrystalline Semiconductors
A polycrystalline material consists of crystal grains that are randomly oriented with respect to each
other. Between two grains a (large-angle) grain boundary (see also Sect. 4.4.3) exists. An important
parameter is the grain size and its distribution. It can be influenced via processing steps such as
annealing. Polycrystalline semiconductors are used in cheap, large-area applications such as solar
cells (e.g. polysilicon, CuInSe 2 ) or thin-film transistors (poly-Si) or as n-conducting contact material
in MOS diodes (poly-Si) as shown in Fig. 3.13 (see also Fig. 21.29). Polycrystalline material can be
fabricated from amorphous material using annealing procedures as discussed in Sect. 24.6.1 for silicon.
3.3.7 Amorphous Semiconductors
An amorphous material lacks the long-range order of the direct lattice. It is disordered on the atomic
scale. Historically, amorphous Se (a-Se) has been investigated first; since the 1950’s amorphous chalco-