Influence of film thickness on the physical properties of manganite heterojunctions

Abstract

Rectifying and photoelectronic properties of the La0.67Ba0.33MnO3/SrTiO3:Nb junctions with the film thickness from d=0.5 to 30 nm have been systematically studied. It is found that the electronic transport of the junction is dominated by quantum tunneling or thermoionic emission when film thickness is below or above 1 nm. The rectifying ratio and ideality factor, correspondingly, experience a sudden change as film thickness grows from 0.5 to 1 nm and a smooth variation with film thickness above 1 nm. The threshold film thickness for the establishment of a mature depletion layer is therefore 1 nm. The photoemission properties of the junctions also exhibit a strong dependence on film thickness. As experimentally shown, the photocurrent vanishes in the zero thickness limit, and grows rapidly with the increase in film thickness until d=6 nm, where a maximal photocurrent of ∼770 nA/mm2 under the irradiance of the laser of 5 mW and 532 nm is obtained. After this maximum, an increase-to-decrease turning appears with further increasing film thickness. Taking into account the finite diffusion distance of the photocarriers and the strain-enhanced charge trapping in ultrathin film junctions, a theoretical description that well reproduces the experiment results can be obtained, which reveals the severe depression of finite diffusion distance of the extra carriers on photocurrent. The maximal diffusion distance thus obtained is ∼3.5 nm. Similar analyses have been performed for the La0.67Ca0.33MnO3/SrTiO3:Nb junctions, and the corresponding diffusion distance there is ∼1.5 nm.

Photoelectronic behaviors of bilayer ultrathin films manganite-based heterojunctions

“…The incorporation of buffer layers obviously affects the interfacial state of the bilayer film junctions, modifying the interfacial barrier and depletion width 13,16 and therefore generation and diffusion of extra charge carriers excited by laser illumination. 17 Typical rectifying behaviors as previously reported are observed (not shown), which confirms the presence of builtin electric field at the interface of the junctions. Electrons in valence band can be excited by laser irradiance to conduction band when photon energy is high enough, and the photocarriers thus produced will be swept to the two sides of the depletion layer by internal field, forming photocurrent.…”

“…With the increase of the LMO layer thickness, for the LMO(t)/STON junctions, the photocurrent first increases rapidly and then, after a maximum, decreases slowly, similar to the results previously reported. 17 Mechanisms for the peculiar photoelectric behaviors of the bilayer junctions deserve further study. The introduction of a buffer layer will modify the interface structure of the junction, including the electronic structure of films and the interfacial barrier/depletion width of the junction, and therefore, the photoelectronic process of junctions.…”

“…Based on the technique described in Ref. 17, a theoretical I ph -t can be deduced after considering the decay of laser in the film and the diffusion of the photocarriers. The corresponding results are shown by the solid line in Fig.…”

“…17 Incorporation of the LMO layer has considerably modified the interface state of the junction, giving nonequilibrium charge carriers' unique dynamic characteristics.…”

Abundant photoelectronic behaviors of La 0.67 Sr 0.33 MnO 3 /Nb:SrTiO 3 junctions

“…For the La 1−x Sr x MnO 3 /Nb:SrTiO 3 heterojunction, more interesting, magnetic, electronic and transport properties can be quite different when the film thickness of La 1−x Sr x MnO 3 film decreases, particular in several nanometer. [15][16][17][18] However, most of the previous studies focused on thick manganite films of junctions at room temperature. The photovoltaic effect of thin film junctions at low temperature is not very clear and deserves further study.…”