364
12 Heterostructures
Fig. 12.19 1 × 1 mm 2 top view with a differential interference contrast microscope of a 1.3 µm thick GaN layer grown
on Si(111). Reproduced with permission from [1156], ©2000 IPAP
Fig. 12.20 a, b 10 nm thick Ge layer on Si (100) deposited at room temperature with MBE and annealed up to 770 ◦ C
without (a) and with (b) Sb surfactant. Adapted from [1165]. c Cross-section TEM image of a heterostructure of 70
monolayers germanium on Si (111), grown by MBE with Sb surfactant. The horizontal arrow labeled ‘I’ denotes the
position of the interface. The arrows labeled ‘D1’ and ‘D2’ denote the positions of partial dislocations (cmp. Fig. 4.20).
Adapted from [327]
This is a serious problem for the growth of embedded layers of the type A–B–A. If the embedded film
grows well, the capping does not and vice versa.
In the case of Ge on Si, Ge has the lower surface free energy than Si. Ge grows on Si in StranskiKrastanow mode [1158] (Fig. 12.20a). Si grows both on Ge(001) and Ge/Si(001) in a Volmer-Weber
mode [1159] causing severe problems for the fabrication of Si/Ge/Si quantum wells or superlattices. A
substantial modification of growth mode can be achieved by using a third element C as a capping layer,
saturating surface bonds. It lowers the surface free energy of both materials A and B, thus favoring
wetting of the substrate. Such element C is called surfactant (surface-active species) [1160, 1161].
Typical examples are As [1160] or Sb [327] on Si and Ge (Fig. 12.20b). Also the surfactant modifies
defect nucleation and can lead to defect-free epitaxial Ge/Si layers (Fig. 12.20c). Surfactants have also
been described for the growth of compound semiconductors, e.g., In [1162] or Sb [1163, 1164] for
GaAs.
12 Heterostructures
Fig. 12.19 1 × 1 mm 2 top view with a differential interference contrast microscope of a 1.3 µm thick GaN layer grown
on Si(111). Reproduced with permission from [1156], ©2000 IPAP
Fig. 12.20 a, b 10 nm thick Ge layer on Si (100) deposited at room temperature with MBE and annealed up to 770 ◦ C
without (a) and with (b) Sb surfactant. Adapted from [1165]. c Cross-section TEM image of a heterostructure of 70
monolayers germanium on Si (111), grown by MBE with Sb surfactant. The horizontal arrow labeled ‘I’ denotes the
position of the interface. The arrows labeled ‘D1’ and ‘D2’ denote the positions of partial dislocations (cmp. Fig. 4.20).
Adapted from [327]
This is a serious problem for the growth of embedded layers of the type A–B–A. If the embedded film
grows well, the capping does not and vice versa.
In the case of Ge on Si, Ge has the lower surface free energy than Si. Ge grows on Si in StranskiKrastanow mode [1158] (Fig. 12.20a). Si grows both on Ge(001) and Ge/Si(001) in a Volmer-Weber
mode [1159] causing severe problems for the fabrication of Si/Ge/Si quantum wells or superlattices. A
substantial modification of growth mode can be achieved by using a third element C as a capping layer,
saturating surface bonds. It lowers the surface free energy of both materials A and B, thus favoring
wetting of the substrate. Such element C is called surfactant (surface-active species) [1160, 1161].
Typical examples are As [1160] or Sb [327] on Si and Ge (Fig. 12.20b). Also the surfactant modifies
defect nucleation and can lead to defect-free epitaxial Ge/Si layers (Fig. 12.20c). Surfactants have also
been described for the growth of compound semiconductors, e.g., In [1162] or Sb [1163, 1164] for
GaAs.