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(a) Schematic of the sample. The thickness of the AlGaAs varies from 20 to 300 nm. (b) Electron micrograph of sidewall. (c) Photoresist and sidewall after wet etch. (d) After short microwave ash (e) Biasing of devices used in this paper (Refs. 6 and 7). (f) An alternative method of making undoped structures (Refs. 3 and 8).
Hall and Shubnikov–de Haas oscillations in a very shallow 2DEG formed 30 nm below the surface (wafer V627).
Data from the wafers grown in two MBE chambers. The effect of the surface states are clearly seen in the and samples. The limit to the mobility of a shallow 2DEG comes from the charge in the surface states [Eq. (7)]. The A wafers were grown on the same day, whereas the V wafers were grown under nominally same conditions but not on the same day. This probably led to a small variation in the condition of the growth chamber.
Parameters extracted from data in Fig. 3. For a note on fit-error see Ref. 15.
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