512
20 Transparent Conductive Oxide Semiconductors
Fig. 20.1 Historical
development of the
resistivity of doped ZnO
(circles), In 2 O 3 (squares)
and SnO 2 (diamonds) TCO
films. Adapted from [1665]
Fig. 20.2 Practical TCO
materials
mostly n-conducting. Also p-conducting TCOs have been reported, e.g. CuAlO 2 delafossite [1667]
with room temperature conductivity of σ = 1 S/cm, ZnIr 2 O 4 [1668] with σ = 2 S/cm and ZnCo 2 O 4
spinel [1669] with σ = 20 S/cm. However, there has been so far no report on a practical transparent
highly conductive p-type electrode.
The term ITO stands for a variety of Sn-doped indium oxide (In 2 O 3 ) materials, the Sn content being
typically in the 5–10% range but not strictly defined. The crystal structure of In 2 O 3 [1670] is shown in
Fig. 20.3. The effect of the replacement of indium by tin atoms in In 2 O 3 on mechanical, electrical and
optical properties of ITO has been calculated in [1671] using DFT. In Fig. 20.4 the band structures of
pure In 2 O 3 and (Sn 0.065 In 0.935 ) 2 O 3 (one out of 16 indium atoms was replaced in the calculation) are
compared [1672]. The fundamental band gap is slightly lowered, the high doping introduces a gigantic
Burstein-Moss shift. Additionally another band gap opens that splits the lowest conduction band. Also
the conduction mechanism in amorphous oxides has been discussed [151].
20.3 Properties
The best conductivity of TCOs is in the range of 10
−4
cm for the specific resistivity. Such value is
about three orders of magnitude smaller than that of metals. However, the TCO meanwhile is highly
transparent in the visible region, while metals become transparent only in the UV region because of
their high plasma frequency (cf. Sect. 9.9.1).
The conduction mechanism in ZnO:Al is band transport in a highly doped semiconductor. The
carrier concentration is typically around 10
21 cm
−3 . One of the best results is a (Hall) mobility of
47.6 cm
2 /Vs, leading to a specific resistivity of 8.5 × 10
−5
cm [1673]. The mobility is limited by
20 Transparent Conductive Oxide Semiconductors
Fig. 20.1 Historical
development of the
resistivity of doped ZnO
(circles), In 2 O 3 (squares)
and SnO 2 (diamonds) TCO
films. Adapted from [1665]
Fig. 20.2 Practical TCO
materials
mostly n-conducting. Also p-conducting TCOs have been reported, e.g. CuAlO 2 delafossite [1667]
with room temperature conductivity of σ = 1 S/cm, ZnIr 2 O 4 [1668] with σ = 2 S/cm and ZnCo 2 O 4
spinel [1669] with σ = 20 S/cm. However, there has been so far no report on a practical transparent
highly conductive p-type electrode.
The term ITO stands for a variety of Sn-doped indium oxide (In 2 O 3 ) materials, the Sn content being
typically in the 5–10% range but not strictly defined. The crystal structure of In 2 O 3 [1670] is shown in
Fig. 20.3. The effect of the replacement of indium by tin atoms in In 2 O 3 on mechanical, electrical and
optical properties of ITO has been calculated in [1671] using DFT. In Fig. 20.4 the band structures of
pure In 2 O 3 and (Sn 0.065 In 0.935 ) 2 O 3 (one out of 16 indium atoms was replaced in the calculation) are
compared [1672]. The fundamental band gap is slightly lowered, the high doping introduces a gigantic
Burstein-Moss shift. Additionally another band gap opens that splits the lowest conduction band. Also
the conduction mechanism in amorphous oxides has been discussed [151].
20.3 Properties
The best conductivity of TCOs is in the range of 10
−4
cm for the specific resistivity. Such value is
about three orders of magnitude smaller than that of metals. However, the TCO meanwhile is highly
transparent in the visible region, while metals become transparent only in the UV region because of
their high plasma frequency (cf. Sect. 9.9.1).
The conduction mechanism in ZnO:Al is band transport in a highly doped semiconductor. The
carrier concentration is typically around 10
21 cm
−3 . One of the best results is a (Hall) mobility of
47.6 cm
2 /Vs, leading to a specific resistivity of 8.5 × 10
−5
cm [1673]. The mobility is limited by