GaAs (001) - (2x4) Rekonstructions

The (2x4) is the typical reconstruction during MBE growth of (001) GaAs. Three different reconstructions with a (2x4)-symmetry are known. They are named with increasing arsenic coverage alpha, beta and gamma. The coverage is 0.5, 0.75 and one monolayer of arsenic.


The surfaces show different diffraction pattern in RHEED [Farrell90].


In RAS the differences are even bigger [Rumberg95].

Because the (2x4) is the typical reconstruction under MBE-conditions, it is very well investigated. The first models were just from simulations of the RHEED intensities together with theoretical calculations of favourable dimer configurations. They have leaded to these models for the three different phases:

From RHEED and STM investigation of samples prepared by MBE these models for the (2x4)-reconstruction were constructed [Farrell90], [Biegelsen90].

Further investigations of decapped as of quenched sampled directly from MBE have changed the picture for the ß(2x4) and therefore also of the rest. The structure of this phase is supposed to consist mainly of a two upper, one lower arsenic dimer arrangement. The existence of the gamma phase is completely questioned, see discussion below.

Newer investigations with STM of decapped samples of the (2x4) [Hashizume95].

The gamma(2x4)

The existence of the gamma(2x4) is questioned as a stable reconstruction [Hashizume95]. Also the gamma phase is only seen in the RHEED pattern, while the STM-images are quite similar to the one of a beta(2x4). Furthermore exists to this RHEED pattern a many RAS spectra, so the "typical" spectrum given above shows only the general trend.

If the gamma(2x4) exist, it arsenic coverage is about 1.0 monolayers.

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last change: 12.12.1996