A high-mobility two-dimensional electron gas at the spinel/perovskite interface of γ-Al2O3/SrTiO3

Abstract

The discovery of two-dimensional electron gases at the heterointerface between two insulating perovskite-type oxides, such as LaAlO 3 and SrTiO 3 , provides opportunities for a new generation of all-oxide electronic devices. Key challenges remain for achieving interfacial electron mobilities much beyond the current value of approximately 1,000 cm 2 V -1 s -1 (at low temperatures). Here we create a new type of two-dimensional electron gas at the heterointerface between SrTiO 3 and a spinel g-Al 2 O 3 epitaxial film with compatible oxygen ions sublattices. Electron mobilities more than one order of magnitude higher than those of hitherto-investigated perovskite-type interfaces are obtained. The spinel/perovskite twodimensional electron gas, where the two-dimensional conduction character is revealed by quantum magnetoresistance oscillations, is found to result from interface-stabilized oxygen vacancies confined within a layer of 0.9 nm in proximity to the interface. Our findings pave the way for studies of mesoscopic physics with complex oxides and design of high-mobility all-oxide electronic devices.

Insulator-to-Metal Transition at Oxide Interfaces Induced by WO3 Overlayers

“…(2), we find a surprisingly high value m * = 5.6 m e . Considering the enhanced mobility of carriers in the WO 3 /LAO/STO system, in fact, one would expect a decreased effective mass, while in this case m * is three times larger than typical observations in LAO/STO heterostructures [17,35].…”

“…In order to promote high electron mobility, it is crucial to confine donor sites away from the conducting plane, without preventing the 2DES formation in the STO top layers. Previous attempts to control the defect concentration profile and thus enhance the mobility involved the use of crystalline insulating overlayers [14,15], adsorbates [16], amorphous materials [17] and even thin metallic layers [18,19]. A promising material to control defect formation is tungsten oxide WO 3 .…”

Two-dimensional electron gas in a modulation-doped SrTiO3/Sr(Ti, Zr)O3 heterostructure

“…24) results in lower carrier densities. Prior studies of 2DEGs in SrTiO 3 found upwards of 60%-95% of carriers in the 2DEG to not give rise to oscillations, 14,[31][32][33][34] which is likely due to disorder limiting the mobility of a significant fraction of the carriers, preventing oscillations to be resolved for all subbands.…”

Quasi-two-dimensional electron gas at the epitaxial alumina/SrTiO3 interface: Control of oxygen vacancies

“…[18][19][20][21][22][23][24][25][26][27]31,32 Since this metallic layer results from the formation of oxygen vacancies near the interface, it characteristically vanishes with oxygen atmospheric annealing. [23][24][25][26][27] One such heterostructure is alumina/STO. Given the context of archetypical 2DEG LaAlO 3 /STO, where competing mechanisms 30 (including polar catastrophe, 10-15 cation exchange, 16,17 and oxygen vacancies [18][19][20][21][22][23][24][25][26][27] ) have been widely investigated and debated, the alumina/STO 2DEG offers an opportunity to isolate the role of oxygen vacancies.…”

“…[18][19][20][21][22][23][24][25][26][27] Under certain conditions, it is energetically favorable for oxygen atoms near the interface to diffuse out of the STO during the initial stages of growth, stabilizing a confined conducting layer. [18][19][20][21][22][23][24][25][26][27]31,32 Since this metallic layer results from the formation of oxygen vacancies near the interface, it characteristically vanishes with oxygen atmospheric annealing. [23][24][25][26][27] One such heterostructure is alumina/STO.…”