Yes but  it is described as -1-1-1

It is a chemical difference-one side Ga and the opposite As, different etching figure. Read: Z. Liliental-Weber and L. Parechanian_Allen; Applied Physics Letters 01/1986; 49:1190-1192

(-1-1-1)

very good question, indeed.

Yes, they are (111)B on the back side.

It is not evident  whether they are also epi-ready on the back side or not. It depends on the manufacturer process. But if you want them epi-ready, make a UV-ozone oxidation. See:

Garcia, Fontaine, and Munoz-Yagüe

Appl. Phys. Lett., Vol. 66, No. 5, 30 January 1995

I believe so but probably both sides need to be prepared epi-ready

GaAs(111)A differs sufficiently from GaAs(111)B from the point of view for diggerent epi-technics. To the best of my knowledge, the A-side (i.e. Ga-atoms side) is prefered for most of epitaxial methods due the better stability connected with the low partial pressure of Ga-atoms compared to As-ones. So, the innitial growth (at same another conditions) confirms better on A-side than on B-one. But the above mentioned is not absolutely true for the today-s well-developed epitaxial methods and growth porpose.

In my opinion it is better to obtain a GaAs  wafer with a defined epi-ready one side  - A or B - as you prefere. Double-side polished wafer is usually not double-side epi-ready, because it is difficult to save the two sides free of microcracs, and more over - to recognize which is A or B side.

 (111)A  is the termination with Ga

(111)B  is the termination with As

I have no experineces with double polished side GaAs wafers, but it is clear that the mechanical-chemical polishing destroys the "normal" surfaces (the surface state situation like surface charge, dislocation density, etc. differe on both side) and probably in different way because you can't keep the the same conditions for both side processes.

For example there have been enough specic surface preparations actions for one sided wafer technology before the LPE process getting the pin GaAs structures for what we made later on the DLTS experiments (the wafer manufacturer was the Clifton Ltd ( www. clifton.ee )). You have to be aware that in case of double sided epigrowth, the result you will get could be not the similar due to different growth conditions for different sides, and if the similar physical parameters for epylayers on both sides are needed, you will be probably in difficulties.

I guess that the differences in orientation on both surfaces could be technologically possible for GaAs wafers as well (it hasn't been in focus of our interest in past), but we have seen such a surface behavior very clearly in case of 4H-SiC wafers by realization of Schottky structures using the diffusion welding metallization technology for simultaneous both side contacs manufacturing.

normally this kind of substrates are prepared to be polished on both sides

So the user can select the adequate orientation for their experiments

Growth on (111) is very different from (11-1) as the latter has a low growth rate and the (111) a 100 times higher growth rate surface in GaAs, see L. Hollan and C. Shiller, J. Crystal Growth 13/14, 319 (1972) and W. Shaw, J. Electrochem. Soc. 115, 405 (1968). The reason is the stability of the different surface reconstructions on these orientations.

Hence there in practive is no stable (111) surface obtained. Because the higher growth rate results from a strong sticking and thus a very low mobility on (111). However, a (111) surface can be stable (thermodynamically) at low V/III ratios (i.e. a very low growth rates for near equilibrium and low arsenic pressure). See the calculated WUlff plot (from A. Kley at FHI-Berlin 1997) In practice this is almost impossible to achieve in MOVPE but maybe possible via MBE.

About double side substrates: As written above those are first polished on one side, then mounted (glued) on that polished side and the final surface CMP is done; this is also done using a much finer polishing paste. While both side may look shiny, one side is much flatter and has much less polishing damage than the other. For epitaxy one the backside (and generally for any GaAs growth) you could try to etch the surfaces. An epi-ready ozone treatment tend to fail on high-index GaAs surface. If you attempt growth with MOVPE, a long anneal in H2 and AsH3 at 650°C may help before growth.