To me, GaAs has a cubic structure with 4 fold symmetry. Why are some properties an-isotropic? Can you propose some literature?
Dear Kamran, the two cleavage planes of GaAs contains a full set of in-plane directions; as GaAs is a crystallographically polar material, this implies that each direction can be either Ga or As (that is, the corresponding planes normal to these directions are either Ga- or As-terminated). These differently-terminated planes react differently to specific (i.e., anisotropic) etch solutions. Now, each cleavage plane contains only one type (either Ga- or As-terminated planes when referred to the (100) wafer surface, which explains the reported different etch behavior of cleavage planes to etching of (100)-GaAs wafers
Dear Kamran, the two cleavage planes of GaAs contains a full set of in-plane directions; as GaAs is a crystallographically polar material, this implies that each direction can be either Ga or As (that is, the corresponding planes normal to these directions are either Ga- or As-terminated). These differently-terminated planes react differently to specific (i.e., anisotropic) etch solutions. Now, each cleavage plane contains only one type (either Ga- or As-terminated planes when referred to the (100) wafer surface, which explains the reported different etch behavior of cleavage planes to etching of (100)-GaAs wafers
I am not sure whether I understand your question.
As pointed out by Dubecky, GaAs has a diamond-like structure with two different sets of FCC lattices which Wyckoff positions differ (1/4,1/4,1/4). Then both (011) and (0-11) or (110) and (1-10) surfaces usually described are identical and non-polar.
On the other hand, smoothly cleaved planes of (100) or (111) will cause Ga- or As-terminated surfaces. Consider the ionic character of this compounds, these surfaces are considered as polar.
Hello Kamran,
besides anisotropic etching you will find an anisotropic refractive index (called indicatrix) resulting in Faraday effect for certain light propagation directions. This is due to the fact of the above mentioned 1/4 diagonal displacement of the fcc-lattices. So in particular orientations you can differentiate between the lattices when you rotate them 180 degrees. This would not be true when the displacement would have been 1/2 diagonal.
A good source for such questions is always Landold Börnstein from Springer Materials (see link below)
http://www.springermaterials.com/navigation/#n_240790_Gallium+arsenide+%2528GaAs%2529
Dear all, many thanks for your time to answer this question. Now, I have a better understanding when looking at your answers!
Elena Shishonok
All planes of multiplicity {110} form the singlet peak in XRD patterns of a FCC crystal if the crystal lattice is perfect. No difference can be obtained in etching. If some planes of the crystals are distroyed (imurities, vacancies) you will obtain a split of the XRD reflexes and results of etching are different.
Because in one case the surface is terminated by Ga atoms, in the other by As atoms.
Make an stick and balls model of both susfaces and you will see the difference.
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