Pulse and Compliance Current-Dependent Negative Differential Resistance in BaTiO₃/Nb:SrTiO₃ Heterojunctions

Abstract

The negative differential resistance (NDR) is closely related to the pulse and compliance current (CC) but not ferroelectric polarization in BaTiO 3 /Nb:SrTiO 3 heterojunctions. The NDR feature shows an opposite trend on the positive (+V P ) and negative pulse (−V P ) and the same trend on pulse amplitude and width while maintaining the same polarity. When the applied pulse was small or short, the NDR characteristics are almost not influenced. With increase of the +V p (−V p ) amplitude or width, NDR enhances (reduces) while shifting to a smaller (bigger) negative bias voltage (−V b ), and the low resistance state (LRS) reduces (enhances) while the high resistance state (HRS) almost remains unchanged. Furthermore, as CC increases, the NDR enhances markedly and barely shifts, while the LRS and HRS almost remain unchanged. Interestingly, the NDR location and LRS exhibit the same dependence on the amplitude/width of ±V p and CC. The above behaviors of NDR can be attributed to the variance of oxygen vacancy (V o ) concentration and depletion layer width. It is beneficial for the development of NDR devices.

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“… 21 For ferroelectric material, piezoresponse (PR) hysteresis loop is expected to deform and even collapse when V ac is above the coercive voltage because the polarization switching counteracted the PR. 22 The result in Fig. 3(h) is consistent with the literature, which suggests ferroelectric properties of BGFNO films.…”

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“…. 23 As shown in the illustration of Figure 3c, the logarithm of conductivity (lnσ) has a linear relationship with 10 3 /T, which further confirms the mechanism of SCLC at the HRS and the formation/rupture of oxygen vacancy CFs for the TS.…”

“…8,16 In our previous work, the role of ferroelectric polarization has been eliminated by piezoelectric force microscope spectroscopy. 23 The mechanism of TS can be divided into ion (cation, anion) migration and phase transition. The type of cation and anion migration corresponds to the formation/ rupture of conductive filaments (CFs) by active metal ions such as Ag/Cu and oxygen vacancies (V o ), 8,11,12,24 while the phase-transition type is induced by a metal−insulator phase transition.…”

“…As I cc increases, V th almost remains the same value, while the absolute value of V hold decreases. This can be understood from the fact that when I cc is very small, the electrons cannot drift away from the BTO/NSTO interface; 23 thus, the concentration of V o +/2+ is too low to cause a sudden change in the current, and the TS is absent. As I cc increases, more electrons can drift away from the BTO/NSTO interface, and the concentration of V o +/2+ will increase.…”

“…This transition can be understood from the electron trapping/detrapping at the BTO/NSTO interface. When the negative pulse is applied, the V o +/2+ traps electrons and become an electrically neutral state, and the effective accumulation of V o +/2+ at the BTO/ NSTO interface attenuates, 23 resulting in thinner/less CFs and a smaller conductance. When the pulse interval is small, the device conductance decreases with an increase in the pulse numbers.…”