The (2x1) is the phosphorous rich reconstruction, found in MBE, GS-MBE [Yang94] and CBE [Zorn96]. There are no information about the mircroscopic structure yet, although one might speculate, if it is a disordered GaAs-like (2x4).
Two slightly different RAS-spectra have been found.
Any contribution is welcome.
last change: 5.6.1996