New insight into Fermi-level unpinning on GaAs: Impact of different surface orientations
We have systematically studied NMOSFETs, MOSCAPs, and the interfacial chemistry on GaAs (100), (110), (111)A and (111)B-four different crystalline surfaces with direct ALD Al2O3. We found that a much higher drain current on GaAs(111)A NMOSFET can be achieved compared to that obtained on the other 3 surfaces. Also, the results of MOS-CAPs and the interfacial chemistry obtained on the (111)A surface are very different from those others. These experimental results conclusively demonstrate that Fermi-level on the GaAs (111)A surface is indeed unpinned and Fermi-level pinning is not an intrinsic property of GaAs, but is orientation dependent thus related to surface chemistry.