Modulation-doped oxide two-dimensional electron gas formed at the LaMnO (LMO) buffered disorderd-LaAlO/SrTiO (-LAO/LMO/STO) heterointerface provides new opportunities for electronics as well as quantum physics. Herein, we studied the dependence of Sr-doping of LaSrMnO (LSMO, = 0, 1/8, 1/3, ½, and 1) spacer on the transport properties of -LAO/LSMO/STO in order to determine the effects of the filling of Mn subbands as well as the LSMO polarity on the modulation-doping. Upon increasing the LSMO film thickness from 1 unit cell (uc) to 2 uc, a sharp metal to insulator transition of interface conduction was observed, independent of . The resultant electron mobility is higher than 1900 cm V s at 2 K, which increases upon decreasing . The sheet carrier density, on the other hand, is in the range of 6.9 × 10∼1.8 × 10cm (0.01 ∼ 0.03 /uc) and is largely independent on for all the metallic -LAO/LSMO (1 uc)/STO interfaces. These results are consistent with the charge transfer induced modulation doping scheme and clarify that the polarity of the buffer layer plays a trivial role on the modulation doping. The negligible tunability of the carrier density could result from the reduction of LSMO during the deposition of disordered LAO or that the energy levels of Mn 3 electrons at the interface of LSMO/STO are hardly varied even when changing the LSMO composition from LMO to SrMnO.
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