This article reviews the major physico-chemical aspects of molecular beam epitaxy (MBE), especially as applied to the deposition of thin epitaxial films of III-V compound and alloy semiconductors. The experimental requirements to achieve the necessary levels of control, purity and uniformity are described first to establish the basic features of the technique. This is followed by a rather detailed treatment of the growth process, including thermodynamic considerations, surface reaction kinetics and film growth dynamics. Because MBE provides a unique means of preparing clean surfaces having controlled stoichiometry and reconstruction, the evaluation of their crystallographic and electronic structure is dealt with at some length. The structure and composition of semiconductor-semiconductor interfaces, together with the formation of quantum wells and periodic superlattices, are topics of increasing importance and as such also receive considerable attention. Dopant incorporation is dealt with rather more briefly by reference to specific examples and finally some mention is made of materials other than III-V semiconductors which have been prepared by MBE.

https://iopscience.iop.org/article/10.1088/0034-4885/48/12/002/pdf

Molecular beam epitaxy

The surface structures formed upon deposition of O2 and Ga2O onto the technologically important arsenic-rich GaAs(001)-c(2×8)/(2×4) surface have been studied using scanning tunneling microscopy and spectroscopy, and the results are compared to density functional theory calculations. O2 chemisorbs by displacing first layer arsenic atoms bonded to second layer gallium atoms. Oxygen chemisorption pins the Fermi level at less than 5% monolayer coverage by creating a donor and acceptor site within the band gap originating from the gallium atom bonded between the two O atoms. In contrast, Ga2O chemisorbs by inserting into arsenic dimer pairs at elevated surface temperatures. A monolayer of Ga2O forms a (2×2) surface structure with a crystalline interface that is electronically unpinned: there are no states within the band gap. The unpinned interface results from Ga2O restoring the surface arsenic and gallium atoms to near-bulk charge.

Scanning tunneling microscopy and spectroscopy of gallium oxide deposition and oxidation on GaAs(001)-c(2×8)/(2×4)

Scanning Tunneling Microscopy of III–V Compound Semiconductor (001) Surfaces

Through rigorous control of preparation conditions, organized monolayers with a highly reproducible structure can be formed by solution self-assembly of octadecanethiol on GaAs (001) at ambient temperature. A combination of characterization probes reveal a structure with conformationally ordered alkyl chains tilted on average at 14 ± 1° from the surface normal with a 43 ± 5° twist, a highly oleophobic and hydrophobic ambient surface, and direct S−GaAs attachment. Analysis of the tilt angle and film thickness data shows a significant mismatch of the average adsorbate molecule spacings with the spacings of an intrinsic GaAs(001) surface lattice. The monolayers are stable up to ∼100 °C and exhibit an overall thermal stability which is lower than that of the same monolayers on Au{111} surfaces. A two-step solution assembly process is observed:  rapid adsorption of molecules over the first several hours to form disordered structures with molecules lying close to the substrate surface, followed by a slow densif...

Molecular self-assembly at bare semiconductor surfaces: preparation and characterization of highly organized octadecanethiolate monolayers on GaAs(001).

K. Jacobi

Papers

Structure and reactivity of GaAs surfaces