Chapter 11
Surfaces
Gott schuf das Volumen, der Teufel die Oberfläche.
God created the bulk; surfaces were made by the devil.
attributed to W. Pauli
Abstract The specifics of semiconductors surfaces, their symmetry, equilibrium crystal shape, reconstructions, steps and faceting are summarized, being important for epitaxy. Physical surface properties
such as vibrational and electronic states are discussed.
11.1 Introduction
Obviously every crystal has a surface all around it, connecting it to the surrounding world. This
represents a brutal perturbation of the bulk periodicity with the consequence of a whole new world of
physics at the surface. With regard to semiconductor technology, the surface properties are of large
importance in a number of instances:
• The crystal growth of semiconductors always occurs at a surface. This subject will be discussed in
Chap. 12.
• The surface is subject to interaction with the chemistry of the surrounding atmosphere. This is
of essential importance for catalysis, e.g., oxidation of CO at noble metals or photocatalytic water
splitting, e.g., using TiO 2 , into oxygen and hydrogen [1051, 1052]. Photocatalysis is briefly discussed
in Sect. 22.1. The interaction and reaction with the surrounding atmosphere can lead modifications
of the semiconductor such as change of conductivity, e.g.., in SnO 2 , which can be used in the
construction of gas detectors [1053–1055].
• Surface passivation and barriers, e.g., using photoresist, silicon oxides or nitrides, are often necessary
in practical devices in order to avoid surface recombination (Sect. 10.12.1) or the interaction with
atmospheric oxygen or water.
But surface physics is interesting in its own right, investigating the properties of a complex mostly
two-dimensional system. ‘Pure’ surfaces are studied using crystals cleaved in ultra-high vacuum or
carefully prepared atomically clean surfaces. A special case are two-dimensional materials, also termed
atomic sheets, such as graphene; these will be discussed in Sect. 13.1.
At the surface the atoms rearrange, compared to their bulk positions, vertically and laterally, also
forming new bonds (surface reconstructions). The mechanical properties (surface phonons) and elec© Springer Nature Switzerland AG 2021
M. Grundmann, The Physics of Semiconductors, Graduate Texts in Physics,
https://doi.org/10.1007/978-3-030-51569-0_11
339
Surfaces
Gott schuf das Volumen, der Teufel die Oberfläche.
God created the bulk; surfaces were made by the devil.
attributed to W. Pauli
Abstract The specifics of semiconductors surfaces, their symmetry, equilibrium crystal shape, reconstructions, steps and faceting are summarized, being important for epitaxy. Physical surface properties
such as vibrational and electronic states are discussed.
11.1 Introduction
Obviously every crystal has a surface all around it, connecting it to the surrounding world. This
represents a brutal perturbation of the bulk periodicity with the consequence of a whole new world of
physics at the surface. With regard to semiconductor technology, the surface properties are of large
importance in a number of instances:
• The crystal growth of semiconductors always occurs at a surface. This subject will be discussed in
Chap. 12.
• The surface is subject to interaction with the chemistry of the surrounding atmosphere. This is
of essential importance for catalysis, e.g., oxidation of CO at noble metals or photocatalytic water
splitting, e.g., using TiO 2 , into oxygen and hydrogen [1051, 1052]. Photocatalysis is briefly discussed
in Sect. 22.1. The interaction and reaction with the surrounding atmosphere can lead modifications
of the semiconductor such as change of conductivity, e.g.., in SnO 2 , which can be used in the
construction of gas detectors [1053–1055].
• Surface passivation and barriers, e.g., using photoresist, silicon oxides or nitrides, are often necessary
in practical devices in order to avoid surface recombination (Sect. 10.12.1) or the interaction with
atmospheric oxygen or water.
But surface physics is interesting in its own right, investigating the properties of a complex mostly
two-dimensional system. ‘Pure’ surfaces are studied using crystals cleaved in ultra-high vacuum or
carefully prepared atomically clean surfaces. A special case are two-dimensional materials, also termed
atomic sheets, such as graphene; these will be discussed in Sect. 13.1.
At the surface the atoms rearrange, compared to their bulk positions, vertically and laterally, also
forming new bonds (surface reconstructions). The mechanical properties (surface phonons) and elec© Springer Nature Switzerland AG 2021
M. Grundmann, The Physics of Semiconductors, Graduate Texts in Physics,
https://doi.org/10.1007/978-3-030-51569-0_11
339