Work function measurements on MBE GaAs(001) layers

Abstract

For the first time, we report contact potential difference (CPD) measurements, using the Kelvin vibrating condensor method, on GaAs (001) layers in situ grown by molecular beam epitaxy (MBE). By using a tungsten rod [calibrated with a W(110) crystal] as reference, absolute determinations of the work function have been done on several surface structures. The MBE layers used for this study were n-type tin-doped 5×1016 cm−3 (μ300K∠4500 cm−2 V−1s−1) and p-type undoped 5×1014 cm−3 (μ300K∠380 cm−2 V−1 s−1) layers. For more than 20 layers tested, no significant work function differences were found between n-type and p-type layers of the same surface structure [c (4×4), c (2×8), (1×6). etc.]. However, important work function differences were observed between the different surface structures. The first result is interpreted as a Fermi level pinning by a high density surface state band (≳1012 cm−2) and compares with recent theoretical and experimental investigations, whereas possible changes in electron affinity due to surface dipole variation with the surface reconstruction are taken into account in the discussion of the second result.