Effect of Sr-doping of LaMnO3 spacer on modulation-doped two-dimensional electron gases at oxide interfaces

TL;DR

This study investigates how Sr-doping in LaMnO3 affects the electronic properties of modulation-doped oxide 2DEGs at heterointerfaces, revealing a sharp metal-insulator transition and high electron mobility largely independent of doping level.

Contribution

It provides new insights into the role of Sr-doping and polarity in tuning the transport properties of oxide heterointerfaces, highlighting the limited impact of doping on carrier density.

Findings

Sharp metal-insulator transition observed with increased LSMO thickness.

Electron mobility exceeds 1900 cm2V-1s-1 at 2 K, increasing with less Sr-doping.

Carrier density remains largely unaffected by Sr-doping levels.

Abstract

Modulation-doped oxide two-dimensional electron gas (2DEG) formed at the LaMnO3 (LMO) buffered disorderd-LaAlO3/SrTiO3 (d-LAO/LMO/STO) heterointerface, provides new opportunities for electronics as well as quantum physics. Herein, we studied the dependence of Sr-doping of La1-xSrxMnO3 (LSMO, x=0, 1/8, 1/3, 1/2, and 1) thus the filling of the Mn eg subbands as well as the LSMO polarity on the transport properties of d-LAO/LSMO/STO. 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 x. The resultant electron mobility is often higher than 1900 cm2V-1s-1 at 2 K, which increases upon decreasing x. The sheet carrier density, on the other hand, is in the range of 6.9E1012~1.8E1013 cm-2 (0.01~0.03 e/uc) and is largely independent on x for all the metallic d-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 3d electrons at the interface of LSMO/STO are hardly varied even when changing the LSMO composition from LMO to SrMnO3.