We introduce a novel lead-free ferroelectric thin film (1-x)BaTiO3-xBa(Cu1/3Nb2/3)O3 (x = 0.025) (BT-BCN) integrated on to HfO2 buffered Si for non-volatile memory (NVM) applications. Piezoelectric force microscopy (PFM), x-ray diffraction, and high resolution transmission electron microscopy were employed to establish the ferroelectricity in BT-BCN thin films. PFM study reveals that the domains reversal occurs with 180° phase change by applying external voltage, demonstrating its effectiveness for NVM device applications. X-ray photoelectron microscopy was used to investigate the band alignments between atomic layer deposited HfO2 and pulsed laser deposited BT-BCN films. Programming and erasing operations were explained on the basis of band-alignments. The structure offers large memory window, low leakage current, and high and low capacitance values that were easily distinguishable even after ~106 s, indicating strong charge storage potential. This study explains a new approach towards the realization of ferroelectric based memory devices integrated on Si platform and also opens up a new possibility to embed the system within current complementary metal-oxide-semiconductor processing technology.

Zincblende-wurtzite polytypism in III−V nanowires has been of great interest for a long time. However, full understanding and control over the crystal phase is still lacking.Here, we propose a model for the morphologies and related crystal phases of vapor−liquid− solid III−V nanowires by considering the minimum surface energies of different side wall facets as a function of the droplet contact angle. On the basis of the recent experimental data and earlier theoretical calculations of the surface energies, a simple classification of the possible growth modes is presented. It shows that the wurtzite phase forms in vertical nanowires at intermediate contact angles whereas the zincblende phase is predominant for vertical or inverse-tapered nanowires with a truncated top at larger contact angles. The small stable contact angle corresponds to faulted wurtzite−zincblende intermix. Pure zincblende phase is possible for even smaller contact angles only in the kinetic growth regimes. The wurtzite and zincblende domains are highly sensitive to surface energetics. Using the model, we explain why most gold-catalyzed GaAs nanowires are wurtzite whereas most gallium-catalyzed GaAs nanowires are zincblende and why it is more difficult to obtain pure wurtzite GaP nanowires. We present experimental data on such GaP NWs grown by gold-catalyzed metal organic molecular beam epitaxy and interpret them within the model. Overall, the proposed picture gives a clear route for the crystal phase engineering in III−V nanowires.

Semiconducting III-V materials exhibiting piezoelectric properties are much sought after due to their potential applications in piezotronic and piezophototronic devices. Nanowires of III-V semiconductors are particularly interesting in this respect due to the occurrence of the wurtzite (WZ) structure commonly associated with enhanced piezoelectric properties in these materials, as opposed to the zinc blende (ZB) structure that is typically observed in the bulk. However, direct measurements of the piezoelectric properties of III-V nanowires using piezo-response force microscopy (PFM) is challenging, and the analysis and interpretation of such measurements is far from trivial. Here we present detailed finite element simulations of single GaAs nanowires, with both WZ and ZB crystalline structure, scanned by an atomic force microscope tip in PFM mode, demonstrating the effect of the non-uniform electric field between the tip and nanowire, scan direction as well as nanowire orientation on the resulting PFM signal. We also report PFM data from single GaAs and InP nanowires with both ZB and WZ structure, grown by molecular beam epitaxy, based on a novel PFM studies on single III-V nanowires 2 non-destructive intermittent contact PFM mode. We explain our experimental data in the framework of our simulations, and for the first time, extract an experimental value for the axial piezoelectric coefficient of WZ InP, d 33 = 0.7 − 1 pm/V. The methods and analysis described here are particularly relevant for the investigation of piezoelectric properties in a wide range of semiconducting III-V nanowire systems.

We report lead-free ferroelectric based resistive switching non-volatile memory (NVM) devices with epitaxial (1-x)BaTiO3-xBiFeO3 (x = 0.725) (BT-BFO) film integrated on semiconducting (100) Nb (0.7%) doped SrTiO3 (Nb:STO) substrates. The piezoelectric force microscopy (PFM) measurement at room temperature demonstrated ferroelectricity in the BT-BFO thin film. PFM results also reveal the repeatable polarization inversion by poling, manifesting its potential for read-write operation in NVM devices. The electroforming-free and ferroelectric polarization coupled electrical behaviour demonstrated excellent resistive switching with high retention time, cyclic endurance, and low set/reset voltages. X-ray photoelectron spectroscopy was utilized to determine the band alignment at the BT-BFO and Nb:STO heterojunction, and it exhibited staggered band alignment. This heterojunction is found to behave as an efficient ultraviolet photo-detector with low rise and fall time. The architecture also demonstrates half-wave rectification under low and high input signal frequencies, where the output distortion is minimal. The results provide avenue for an electrical switch that can regulate the pixels in low or high frequency images. Combined this work paves the pathway towards designing future generation low-power ferroelectric based microelectronic devices by merging both electrical and photovoltaic properties of BT-BFO materials.

Epitaxy of III-V semiconductors on Si gets recent interest for next generation system on heterogeneous chip on wafer. The understanding of band offset is thus necessary for describing the charge transport phenomenon in these heterojunctions. In this work, x-ray photoemission spectroscopy has been used to determine the band offsets in a heterojunction made of InP quantum dots on Si. The valence and conduction band offset was found to be 0.12 eV and 0.35 eV, respectively, with a type-II band lineup. Deviation from theoretical prediction and previously published reports on quasi similar systems have been found and analyzed on the basis of the effect of strain, surface energy, shift in the electrostatic dipole and charge transfer at the interface. The carrier transport mechanisms along with different device parameters in the heterojunction have been studied for a temperature range of 180–300 K. This heterojunction is found to behave as an efficient infrared photodetector with an ON/OFF ratio of 21 at a reverse bias of 2 V. The corresponding rise and decay time was found to be 132 ms and 147 ms, respectively.