Dresden 2003 – scientific programme

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HL: Halbleiterphysik

HL 49: Poster II

HL 49.88: Poster

Thursday, March 27, 2003, 16:30–19:00, HSZ/P2

Anisotropic electron transport in InGaAs heterostructures — •T. Vonau, S. Löhr, Ch. Heyn, and W. Hansen — Institut für Angewandte Physik und Zentrum für

We prepare modulation-doped In_0.75Ga_0.25As/In_0.75Al_0.25As heterostructures embedding an additional strained InAs channel in which a two-dimensional electron gas (2DEG) is confined. The structures are grown by molecular beam epitaxy (MBE) on a GaAs (001) substrate using an InAlAs step graded buffer for relaxation of the lattice mismatch. Three different samples are grown in which the 2DEGs are located 20 nm, 30 nm, and 50 nm beneath the crystal surface, respectively.

We observe strikingly different magneto-conductivities in the two orthogonal ⟨110⟩ directions at a temperature of 4.2 K. An anisotropy of up to 19 % of the electron mobility is found. In addition, the [110] direction shows a pronounced positive parabolic magneto-resistance, which is not observed in [-110]. Both, the mobility anisotropy and the positive magneto-resistance decrease for an increase in electron density as well as for an increasing distance between the 2DEG and the heterostructure surface. The positive magneto-resistance in [110] can be explained by the semiclassical theory on modulated 2DEGs. The origin of the potential modulation is attributed to a nonuniform strain relaxation in the step graded buffer which is related to the asymmetric cross hatch morphology observed at the sample surface.