Significant mobility enhancement in extremely thin highly doped ZnO films

Highly Ga-doped ZnO (GZO) films of thicknesses d = 5, 25, 50, and 300 nm, grown on 160-nm ZnO buffer layers by molecular beam epitaxy, had 294-K Hall-effect mobilities mu(H) of 64.1, 43.4, 37.0, and 34.2 cm(2)/V-s, respectively. This extremely unusual ordering of mu(H) vs d is explained by the existence of a very high-mobility Debye tail in the ZnO, arising from the large Fermi-level mismatch between the GZO and the ZnO. Scattering theory in conjunction with Poisson analysis predicts a Debye-tail mobility of 206 cm(2)/V-s at the interface (z = d), falling to 58 cm(2)/V-s at z = d+2nm. Excellent fits to mu(H) vs d and sheet concentration n(s) vs d are obtained with no adjustable parameters. (c) 2015 AIP Publishing LLC.