Regensburg 2007 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 47: Transport in high magnetic field/quantum-Hall-effect

HL 47.9: Talk

Thursday, March 29, 2007, 17:45–18:00, H14

Temperature dependence of high mobility AlAs quantum wells — •Shivaji Dasgupta, Claudius Knaak, Max Bichler, Anna Fontcuberta-i-Morral, Gerhard Abstreiter, and Matthew Grayson — Walter Schottky Institute, Technische Universität München, Am Coulombwall 3, Garching

We present transport characteristics of high mobility n-type AlAs quantum well (QW) substrates grown on two different facets (001) and (110). Measurements were performed down to 330 mK on van der Pauw geometries and on L-shaped Hall bars with the arms oriented along the crystallographic axes to investigate mobility anisotropies. In the (001) oriented QW, the presence of two degenerate valleys of electrons yields a total isotropic conductance with a mobility of 2.4× 10⁵ cm²/Vs at 1.4 K, with the mobility saturating below 3 K. In the (110) oriented QW, there should be a single valley with an anisotropic conductance. At 1.4 K we obtain mobilities of 3.4× 10³ cm²/Vs along the ⟨ 001 ⟩ branch of the L-shaped Hall bar and 1.8× 10⁴ cm²/Vs on the ⟨ -110 ⟩ branch. The ratio of 5.8 between the two mobilities matches the ratio between the two anisotropic masses, m_l/m_t = 1.1/0.19 = 5.8. The temperature dependence has been analyzed in analogy to mobility limiting processes at low temperatures in GaAs [1], which include remote-ion scattering due to donors, ionized impurity scattering due to interface charge, polar optical phonon scattering, acoustic deformation potential scattering and piezoelectric scattering among others. Evidence of an additional inter-valley scattering term in the mobility will be explored.

[1] Lin, et al. Appl. Phys. Lett. 45, 695 (1984).