Caihong Jia

Origin of attendant phenomena of bipolar resistive switching and negative differential resistance in SrTiO3:Nb/ZnO heterojunctions

Epitaxial ZnO thin films were grown on SrTiO3:Nb (NSTO) substrates by pulsed laser deposition. The NSTO/ZnO heterojunctions exhibit a typical rectification characteristic under a small voltage, while two attendant behaviors of bipolar resistive switching and negative differential resistance appear under a large voltage. The NSTO/ZnO heterojunctions show extremely weak resistance switching hysteresis without applying a forward bias. However, when the forward bias increases to some extent, the hysteresis becomes more and more prominent and negative differential resistance gradually appears. Furthermore, the high resistance state is obtained when sweeping from negative to positive voltage bias, and vice versa. We propose a model for these behaviors at NSTO/ZnO interface, in which the space charge region in ZnO is wide in high resistance state when the interface state is unoccupied, while the space charge region becomes narrower in low resistance state due to Fermi pinning when the interface state is complete...

Control of normal and abnormal bipolar resistive switching by interface junction on In/Nb:SrTiO3 interface

The resistive switching behaviors of indium (In)/Nb:SrTiO3 (NSTO) with different metal/semiconductor contacts are investigated. The In electrodes with the Schottky contacts are fabricated on NSTO surface using direct current reactive magnetron sputtering, and the fresh In is directly pressed to form the Ohmic contact. The device with one Schottky barrier displays a normal bipolar resistive switching (BRS) behavior, while the device with two Schottky barriers shows an abnormal BRS behavior. The results demonstrate that the injection and trapping or detrapping of carriers near the interface between the metal electrode and semiconductor are closely related to the resistive switching performance.

Ferroelectric memristive effect in BaTiO3 epitaxial thin films

Epitaxial BaTiO3 (BTO) films have been grown on Nb-doped SrTiO3 (NSTO) (0 0 1) substrate. The ferroelectric resistive switching effect and memristive behaviours have been observed in Pt/BTO/NSTO heterostructures. It exhibits two resistance states under different polarization, and both current–voltage curves are nonlinear, slightly asymmetric and free of discontinuities, in contrast with what often occurs with other resistive switching devices. In addition, the resistance can be continuously tuned up to 1.3 × 105% by varying pulse voltage amplitudes for the ferroelectric memristor application. Moreover, the device exhibits excellent retention and reproducibility. The above phenomena can be qualitatively explained by considering the modulation of the width and height of the potential barrier at the BTO/NSTO interface by ferroelectric polarization.

Epitaxial growth and optical properties of Al- and N-polar AlN films by laser molecular beam epitaxy

Epitaxial aluminum nitride (AlN) films with c-axis orientation were grown on both (1 1 1) MgO and c-sapphire substrates by laser molecular beam epitaxy. The in-plane epitaxial relationships were determined to be [1 1 ¯ 2 0]AlN||[0 ¯ 1 1]MgO and [1 ¯ 1 0 0]AlN||[1 1 ¯ 2 0]sapphire, and the lattice mismatch was 4.2% and 13.2% for AlN films on MgO and sapphire, respectively. The AlN films were shown to be Al- and N-polar on MgO and sapphire, respectively. The former is assumed to be caused by the centre of inversion symmetry of (1 1 1) MgO substrate, while the latter is due to the O polarity of sapphire. The full-width at half-maximum of the ω-scanning spectrum for AlN film on (1 1 1) MgO substrate is smaller than that on the c-sapphire substrate. The optical band-gap energies for AlN films grown on MgO and sapphire were found to be 5.93 and 5.84 eV, close to the standard band gap of 6.2 eV, and the calculated Urbach energies were 0.27 eV and 0.53 eV, respectively. These results indicate a lower amorphous content and/or less defects/impurities in Al-polar than N-polar AlN.

Epitaxial growth of BaTiO3/ZnO heterojunctions and transition from rectification to bipolar resistive switching effect

Epitaxial BaTiO3/ZnO heterojunctions have been grown on a-plane Al2O3 by pulsed laser deposition. The out-of-plane and in-plane epitaxial relationships of BTO/ZnO/Al2O3 are determined to be (100)BTO//(0002)ZnO//(11 2¯0)Al2O3 and [011]BTO//[2 1¯ 1¯0]ZnO//[0001]Al2O3, respectively. A three-domain-epitaxy growth mode was found to coexist in BaTiO3 films, while ZnO was a single domain epitaxially grown on a-Al2O3. A rectification effect was observed for the BTO films grown at high laser energies of 450 and 320 mJ, while bipolar resistive switching was found for those BTO films grown at low laser energies of 280 and 200 mJ. The transition from the rectification effect to the bipolar resistive switching effect can be understood by the variance of interface state density.