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(Color online) (a) Tube formation process. The built-in strain between lattice mismatched semiconductors is released by removing the sacrificial layer below it. (b) Types of geometries fabricated. (i) Single turn tube. (ii) Multiturn tubes. (iii) Helical coils. Optical image of (c) Hall bar used for measurements and (d) tube formed. (e) Scanning electron micrograph of the tube formed. (f) Two point measurement setup after tube formation. The solid arrows indicate the tube while dotted arrows indicate the direction of rollup.
(Color online) (a) Consists of a transport layer formed by GaAs cap layer followed by , GaAs (Si delta doped), , GaAs over the strained bi-layers of , , and AlAs (sacrificial layer) over GaAs substrate. (b) Simplified band structure of all layers above the sacrificial layer along with Fermi energy. (c) Band structure after illumination showing shift of Fermi level and photoinduced quasi-2D population of carriers. (d) Band structure after application of back gate bias showing expelled carriers from the lower quantum well, populating the 2DEG.
(Color online) Comparison of longitudinal resistance of the planar sample with and without back gate bias. The curve fit shows the change in the peak position with gate bias. Inset shows the four-terminal measurement setup.
(Color online) Comparison of two point magnetoresistance before and after tube formation showing a zero field peak in resistance and negative resistance region at low magnetic fields. Inset shows the ratio of resistance after tube formation to the resistance before tube formation indicating two regimes of electron transport.
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