Single-valley high-mobility (110) AlAs quantum wells with anisotropic mass

Abstract

We studied a doping series of (110)-oriented AlAs quantum wells (QWs) and observed transport evidence of single anisotropic-mass valley occupancy for the electrons in a 150Å wide QW. Our calculations of strain and quantum confinement for these samples predict single anisotropic-mass valley occupancy for well widths W greater than 53Å. Below this, double-valley occupation is predicted such that the longitudinal mass axes are collinear. We observed mobility anisotropy in the electronic transport along the crystallographic directions in the ratio of 2.8, attributed to the mass anisotropy as well as anisotropic scattering of the electrons in the X-valley of AlAs.

Valley degeneracy in biaxially strained aluminum arsenide quantum wells

“…Unconventional facets such as (411) have also proven useful in identifying exchange effects like quantum Hall ferromagnetism in AlAs QWs 6,7 . Evidence for a QW width crossover from double-to single-valley occupation has been shown for (001)AlAs wells 8,9 , as has evidence for single valley occupancy in wide (110)AlAs wells 5 . Dynamic control of the valley degeneracy has been realized with uniaxially strained (001)AlAs QWs to induce valley degeneracy splitting 1,10,11 .…”

“…1) because its heavy anisotropic electron mass allows for large interaction effects 1 , and its near perfect lattice match to GaAs substrates allows for high-mobility, modulationdoped quantum wells (QWs) 2,3 . AlAs/AlGaAs QWs can reach mobilities of the order of µ = 100,000 cm 2 /Vs in (001)-facet QWs 4 and in the high mobility direction of anisotropic (110)-facet QWs 5 . Unconventional facets such as (411) have also proven useful in identifying exchange effects like quantum Hall ferromagnetism in AlAs QWs 6,7 .…”

Optimization of AlAs/AlGaAs quantum well heterostructures on on-axis and misoriented GaAs (111)B

“…1 With near-perfect lattice-match to GaAs, this multivalley semiconductor is further an excellent system for fabrication of high-mobility, modulation-doped quantum wells (QWs), where large progress was recently achieved in (001) and (110)-oriented AlAs/AlGaAs two-dimensional electron systems (2DES) with mobilities in excess of 10 5 cm 2 /Vs. [2][3][4] The three-fold valley degeneracy is broken due to strain and quantum confinement effects in these biaxially strained AlAs/AlGaAs QW heterostructures, leading to either double [in (001)-oriented QWs] or single [in (110)-oriented QWs] valley degeneracy. [2][3][4]8 In addition, a transition between double and single valley degeneracy was observed in piezoelectrically strained (001) AlAs QWs and as a function of QW width, 1 facilitating dynamic control of valley occupancy and tuning of valley effective mass.…”

Steering and collimating ballistic electrons with amphoteric refraction

“…However, they have the same sign unless the signs of m 2x and m 2y are opposite. This is not generally the case in anisotropic semiconductor heterostructures, which include uniaxial compounds (for instance, gallium 0021-8979/2012/112(2)/024318/5/$30.00 V C 2012 American Institute of Physics 112, 024318-1 selenide 13 ), strained AlAs quantum wells, 14 and HgZnTeCdTe type III superlattices, 15 layered biaxial materials such as Hg 3 TeCl 4 , 16 or strained Si, 17 Ge (Ref. 18) and their composites (in Si 1Àx Ge x layers grown on Si wafers the strain is biaxial).…”