Intrinsic Transport Research Articles

Ultraclean suspended monolayer graphene achieved by in situ current annealing

Ultraclean graphene is essential for studying its intrinsic transport properties or fabricating high-performance electronic devices. Unfortunately, the contamination on graphene is unavoidable after microelectromechanical system processing. Here, we report an in situ current-annealing method for achieving ultraclean suspended monolayer graphene. The charge mobility of cleaned graphene reached a surprising 3.8 × 105 cm2 V−1 s−1, one of the highest values ever reported. For the first time, the process of current annealing was recorded under a high-resolution electron scanning microscope. It was demonstrated that temperature was the only dominant factor of the current-annealing process. Meanwhile, the mobility of suspended graphene was found to be highly sensitive to structural defects. The mobility decreased by a factor of over 100 after ion irradiation on graphene. The results revealed the underlying mechanism of current annealing on graphene and provided an effective means of preparing ultraclean graphene membranes.

Transport properties of chemically synthesized MoS2 – Dielectric effects and defects scattering

We report on the electrical characterization of synthetic, large-area MoS2 layers obtained by the sulfurization technique. The effects of dielectric encapsulation and localized defect states on the intrinsic transport properties are explored with the aid of temperature-dependent measurements. We study the effect of dielectric environment by transferring as-grown MoS2 films into different dielectrics such as SiO2, Al2O3, HfO2, and ZrO2 with increasing dielectric permittivity. Electrical data are collected on a statistically-relevant device ensemble and allow to assess device performances on a large scale assembly. Our devices show relative in-sensitiveness of mobility with respect to dielectric encapsulation. We conclude that the device behavior is strongly affected by several scattering mechanisms of different origin that can completely mask any effect related to dielectric mismatch. At low temperatures, conductivity of the devices is thermally activated, a clear footprint of the existence of a mobility edge separating extended states in the conduction band from impurity states in the band-gap.

Nonlinear Microwave Characterization of CVD Grown Graphene

Linear and nonlinear microwave properties of chemical vapor deposition (CVD)-grown graphene are characterized by incorporating a coplanar waveguide (CPW) transmission-line test structure. The intrinsic linear transport properties ( ${S}$ -parameters) of the graphene sample are measured and extracted via a deembedding procedure and then fitted with an equivalent circuit model up to 10 GHz. A statistical uncertainty analysis based on multiple measurements is implemented to estimate the error of the extracted graphene linear parameters as well. Nonlinear properties (second- and third-order harmonics as a function of fundamental input power) of the sample are also measured with a fundamental input signal of 1 GHz. Clear harmonics generated from graphene are observed, while no obvious fundamental power saturation is seen. The measured nonlinearity is applied in a graphene patch antenna case study to understand its influence on potential applications in terms of third-order intermodulation levels.

Intrinsic electrical transport and performance projections of synthetic monolayer MoS2 devices

We demonstrate monolayer (1L) MoS2 grown by chemical vapor deposition (CVD) with transport properties comparable to those of the best exfoliated 1L devices over a wide range of carrier densities (up to ∼1013 cm−2) and temperatures (80–500 K). Transfer length measurements decouple the intrinsic material mobility from the contact resistance, at practical carrier densities (>1012 cm−2). We demonstrate the highest current density reported to date (∼270 μA μm−1 or 44 MA cm−2) at 300 K for an 80 nm long device from CVD-grown 1L MoS2. Using simulations, we discuss what improvements of 1L MoS2 are still required to meet technology roadmap requirements for low power and high performance applications. Such results are an important step towards large-area electronics based on 1L semiconductors.

Observation of Optical and Electrical In-Plane Anisotropy in High-Mobility Few-Layer ZrTe5.

Transition metal pentatelluride ZrTe5 is a versatile material in condensed-matter physics and has been intensively studied since the 1980s. The most fascinating feature of ZrTe5 is that it is a 3D Dirac semimetal which has linear energy dispersion in all three dimensions in momentum space. Structure-wise, ZrTe5 is a layered material held together by weak interlayer van der Waals force. The combination of its unique band structure and 2D atomic structure provides a fertile ground for more potential exotic physical phenomena in ZrTe5 related to 3D Dirac semimentals. However, the physical properties of its few-layer form have yet to be thoroughly explored. Here we report strong optical and electrical in-plane anisotropy of mechanically exfoliated few-layer ZrTe5. Raman spectroscopy shows a significant intensity change with sample orientations, and the behavior of angle-resolved phonon modes at the Γ point is explained by theoretical calculations. DC conductance measurement indicates a 50% of difference along different in-plane directions. The diminishing of resistivity anomaly in few-layer samples indicates the evolution of band structure with a reduced thickness. A low-temperature Hall experiment sheds light on more intrinsic anisotropic electrical transport, with a hole mobility of 3000 and 1500 cm2/V·s along the a-axis and c-axis, respectively. Pronounced quantum oscillations in magnetoresistance are observed at low temperatures with the highest electron mobility up to 44 000 cm2/V·s.

Thin-film composite forward osmosis membranes functionalized with graphene oxide–silver nanocomposites for biofouling control

Innovative approaches to prevent bacterial attachment and biofilm growth on membranes are critically needed to avoid decreasing membrane performance due to biofouling. In this study, we propose the fabrication of anti-biofouling thin-film composite membranes functionalized with graphene oxide–silver nanocomposites. In our membrane modification strategy, carboxyl groups on the graphene oxide–silver nanosheets are covalently bonded to carboxyl groups on the surface of thin-film composite membranes via a crosslinking reaction. Further characterization, such as scanning electron microscopy and Raman spectroscopy, revealed the immobilization of graphene oxide–silver nanocomposites on the membrane surface. Graphene oxide–silver modified membranes exhibited an 80% inactivation rate against attached Pseudomonas aeruginosa cells. In addition to a static antimicrobial assay, our study also provided insights on the anti-biofouling property of forward osmosis membranes during dynamic operation in a cross-flow test cell. Functionalization with graphene oxide–silver nanocomposites resulted in a promising anti-biofouling property without sacrificing the membrane intrinsic transport properties. Our results demonstrated that the use of graphene oxide–silver nanocomposites is a feasible and attractive approach for the development of anti-biofouling thin-film composite membranes.

Diffusive light transport in semitransparent media

Light diffusion is usually associated with thick, opaque media. Indeed, multiple scattering is necessary for the onset of the diffusive regime and such condition is generally not met in almost transparent media. Nonetheless, at long enough times, transport in an infinite thin slab is still determined by a multiple scattering process whose complete characterization is lacking. In this paper we show that, after a short transient, the mean square width of the transmitted intensity still exhibits a simple linear increase with time as predicted by diffusion theory, even at optical thickness as low as one. Interestingly, such linear growth is predicted not to depend neither on the slab thickness nor on its refractive index contrast, yet the accuracy of this simple approximation in the ballistic-to-diffusive regime hasn't been investigated so far. By means of Monte Carlo simulations, we find clear evidence that boundary conditions play an active role in redefining the very asymptotic value of the diffusion coefficient by directly modifying the statistical distributions underlying light transport in such media. In this respect, we demonstrate the need to distinguish between a set of intrinsic and effective transport parameters, whose relation and interplay with boundary conditions remains to be fully understood.

Systematic Study of Widely Applicable N‐Doping Strategy for High‐Performance Solution‐Processed Field‐Effect Transistors

A specific design for solution‐processed doping of active semiconducting materials would be a powerful strategy in order to improve device performance in flexible and/or printed electronics. Tetrabutylammonium fluoride and tetrabutylammonium hydroxide contain Lewis base anions, F− and OH−, respectively, which are considered as organic dopants for efficient and cost‐effective n‐doping processes both in n‐type organic and nanocarbon‐based semiconductors, such as poly[[N,N′‐bis(2‐octyldodecyl)‐naphthalene‐1,4,5,8‐bis(dicarboximide)‐2,6‐diyl]‐alt‐5,5′‐(2,2′‐bithiophene)] (P(NDI2OD‐T2)) and selectively dispersed semiconducting single‐walled carbon nanotubes by π‐conjugated polymers. The dramatic enhancement of electron transport properties in field‐effect transistors is confirmed by the effective electron transfer from the dopants to the semiconductors as well as controllable onset and threshold voltages, convertible charge‐transport polarity, and simultaneously showing excellent device stabilities under ambient air and bias stress conditions. This simple solution‐processed chemical doping approach could facilitate the understanding of both intrinsic and extrinsic charge transport characteristics in organic semiconductors and nanocarbon‐based materials, and is thus widely applicable for developing high‐performance organic and printed electronics and optoelectronics devices.

Inhomogeneous longitudinal distribution of Ni atoms on graphene induced by layer-number-dependent internal diffusion

The intrinsic transport properties, such as carrier mobility and saturation velocity, of graphene are the highest among materials owing to its linear band dispersion and weak backscattering. However, the reported field-effect mobility of transistors using graphene as a channel is much lower than the intrinsic channel mobility. One of the reasons for this low mobility is the high contact resistance between graphene and metals used for the source and drain electrodes, which results from the interfacial roughness. Even Ni, which is a promising contact metal for many materials because of its high adhesion and lower contact resistance, does not meet the requirement as a contact metal for graphene. Noticing that the interfacial roughness between the a metal and graphene is strongly related to the onset of the contact resistance, we performed transmission electron microscopy and photoemission electron microscopy measurements to evaluate the microscopic lateral and longitudinal distributions of Ni atoms at the Ni/graphene interface formed on epitaxial graphene (EG) on 4H-SiC(0001). Our data revealed that the deposited Ni atoms diffused into the EG layers, but they did not reach the EG/SiC interface, and the diffusion was stronger on bilayered graphene than on monolayered graphene. We thus ascribe the layer-number-dependent internal diffusion of Ni atoms in EG as a cause of the microscopic interfacial roughness between graphene and the metal. Ensuring homogeneous distribution of the number of EG layers should be key to lowering the contact resistance.

(Invited) Luminescence Spectroscopy of Metal-Halide Perovskites: A Solution-Processed High-Efficiency Photonic Material

Lead halide perovskites MAPbX3 [MA = CH3NH3, X = Br and I] have recently received much attention as a promising class of photovoltaic, laser, and light-emitting diode (LED) materials that enable low cost and high efficiency. To clarify the physical origin of the highly efficient mutual conversion between light and electricity in MAPbX3, we have studied the optical properties and photocarrier recombination processes in MAPbX3 thin films and single crystals. In this talk, we summarize our recent spectroscopic data of MAPbX3 and discuss their radiative and nonradiative recombination processes with respect to laser, LED, and photovoltaic applications. Highly luminescent materials are required for excellent solar cell (SC) and LED devices, and bright LEDs can also work as high-power SCs. The energy conversion efficiencies of SC and LED devices depend on the luminescence quantum efficiency of the used semiconductor material. Therefore, luminescence spectroscopy is one of the most powerful techniques for characterizing and developing new materials and structures for SC and LED devices. Since solution-processed MAPbX3 thin films show high-efficiency photoluminescence (PL) and electroluminescence (EL), MAPbX3-based diodes should enable excellent SC and LED devices. MAPbX3 perovskites have a direct band-gap structure and large optical absorption coefficients in the visible spectral region [1,2]. Their PL lifetimes are long, resulting in long carrier diffusion length. These intrinsic optical and transport properties are the physical origin of the observed high conversion efficiencies in MAPbX3-based SCs. Time-resolved PL measurements clearly show that the PL decay dynamics are explained by a simple model including single carrier trapping and the radiative electron-hole recombination [3]. The excitation intensity dependence of the PL decay time constant indicates that the density of the carrier traps and recombination centers is extremely low [3,4]. In MAPbX3 single crystals, an initial fast-decay component appears in the PL decay curve, which is not observed in polycrystalline MAPbX3 thin films [5]. Fast carrier diffusion determines the spatial distribution of carriers in the near-surface region. To clarify the impact of the spatial photocarrier distribution on the PL decay, the PL decay dynamics are studied by two-photon excitation spectroscopy [5,6]. Under one-photon excitation, a redshift of the PL peak is observed for later times after photoexcitation. On the other hand, the PL peak exhibits no redshift with time in case of two-photon excitation. In addition, the PL decay time constant for two-photon excitation is much larger than that for one-photon excitation [5,6]. We clearly show that the carrier diffusion process in the near-surface region causes the PL peak shift and the rapid decay of the PL intensity at the initial stage for one-photon excitation. The photon recycling is responsible for slow PL decays and long-range carrier diffusion [5,6]. These unique properties are suitable for photonic devices. Our optical studies provide fundamental information for realization of high-performance devices based on metal halide perovskites.The author would like to thank Y. Yamada, T. Yamada, and A. Wakamiya for discussions. Part of this work was supported by JST-CREST. [1] Y. Yamada et al., Appl. Phys. Express 7 (2014) 032302.[2] Y. Yamada et al., IEEE J. Photovol. 5 (2015) 401.[3] Y. Yamada et al., J. Am. Chem. Soc. 136 (2014) 11610.[4] H. Tahara et al., J. Phys. Chem. C 120 (2016) 5347.[5] Y. Yamada et al., J. Am. Chem. Soc. 137 (2015) 10456.[6] T. Yamada et al., Adv. Electron. Mater. 2 (2016) 1500290.

Topochemical polymerization of diacetylenes

Since the discovery of conducting polymers, they have received considerable attention both from academic and industry due to their attractive advantages of light weight, low cost, and easy processing, which make them demonstrate a wide range of applications. Over the past decades, significant advances have been achieved in this field with the development of high performance polymeric semiconductors and device fabrication techniques. However, there are still many scientific questions existing in this field, such as the unclear charge transport physics in conjugated polymers due to disordered molecular structures in the widely investigated films. Compared to thin films, single crystals possess long-range molecular order, no grain boundaries and no defects, which are seen as the best candidates for revealing the intrinsic charge transport of materials. However, it has been a big challenge for the crystallization of polymers directly from solution, and even is elusive for the conjugated polymers due to their intrinsic electron-rich conjugated backbone structures. Topochemical polymerization where under a certain reaction condition, the preorganized monomer crystals could be directly changed to their corresponding polymer crystals with a minimum amount of atomic and molecular movement, that is realizing the single-crystal-to-single-crystal transformation would provide us a promising solution. Compared to traditional solution process, with this method, we can possibly realize two goals: (1) the controllable synthesis because the first crystal growth process is from the monomer molecules; (2) the possible obtainment of higher molecule-weight polymer chains because we do not need consider their solubility problem like that from solution synthesis.

Highly anisotropic electronic transport properties of monolayer and bilayer phosphorene from first principles

The intrinsic carrier transport dynamics in phosphorene is theoretically examined. Utilizing a density functional theory treatment, the low-field mobility and the saturation velocity are characterized for both electrons and holes in the monolayer and bilayer structures. The analysis clearly elucidates the crystal orientation dependence manifested through the anisotropic band structure and the carrier-phonon scattering rates. In the monolayer, the hole mobility in the armchair direction is estimated to be approximately five times larger than in the zigzag direction at room temperature (460 cm2/V s vs. 90 cm2/V s). The bilayer transport, on the other hand, exhibits a more modest anisotropy with substantially higher mobilities (1610 cm2/V s and 760 cm2/V s, respectively). The calculations on the conduction-band electrons indicate a comparable dependence while the characteristic values are generally smaller by about a factor of two. The variation in the saturation velocity is found to be less pronounced. With the anticipated superior performance and the diminished anisotropy, few-layer phosphorene offers a promising opportunity particularly in p-type applications.

Terahertz Conductivity within Colloidal CsPbBr3 Perovskite Nanocrystals: Remarkably High Carrier Mobilities and Large Diffusion Lengths

Colloidal CsPbBr3 perovskite nanocrystals (NCs) have emerged as an excellent light emitting material in last one year. Using time domain and time-resolved THz spectroscopy and density functional theory based calculations, we establish 3-fold free carrier recombination mechanism, namely, nonradiative Auger, bimolecular electron-hole recombination, and inefficient trap-assisted recombination in 11 nm sized colloidal CsPbBr3 NCs. Our results confirm a negligible influence of surface defects in trapping charge carriers, which in turn results into desirable intrinsic transport properties, from the perspective of device applications, such as remarkably high carrier mobility (∼4500 cm(2) V(-1) s(-1)), large diffusion length (>9.2 μm), and high luminescence quantum yield (80%). Despite being solution processed and possessing a large surface to volume ratio, this combination of high carrier mobility and diffusion length, along with nearly ideal photoluminescence quantum yield, is unique compared to any other colloidal quantum dot system.

A first-principles study on the intrinsic phonon transport of Cu2GeSe3

First-principles calculations are employed to investigate the phonon transport of Cu2GeSe3. The lattice thermal conductivities of Cu2GeSe3 are reproduced. In Cu2GeSe3, the low-frequency phonons lower than 88 cm−1, which comprise of most acoustic modes and a few optical modes, contribute more than 90% to the overall lattice thermal conductivity in Cu2GeSe3. According to the calculations of phonon transport, nanostructuring may be an effective way to reduce the lattice thermal conductivity of Cu2GeSe3. Particularly, at 300 K, the nanostructuring with length scale 100 nm (10 nm) would possibly reduce the thermal conductivity by more than 40% (80%) for Cu2GeSe3. With increase of temperature, the effect of nanostructuring on reducing the lattice thermal conductivity will diminish, due to the decrease in the phonon mean-free path. We further speculate that phonon-band engineering by doping with heavy elements such as Pb may further reduce the lattice thermal conductivity. Our work facilitates deep understanding of the mechanisms of effective reduction of the thermal conductivity by nanostructuring or doping, and helps design better thermoelectric materials.

Low-Temperature Band Transport and Impact of Contact Resistance in Organic Field-Effect Transistors Based on Single-Crystal Films of Ph-BTBT-C10

Even as technology based on solution-processable organic semiconductors advances, questions remain about their charge transport. The hallmark of $b\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}d$ $t\phantom{\rule{0}{0ex}}r\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}s\phantom{\rule{0}{0ex}}p\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}r\phantom{\rule{0}{0ex}}t$ is electron mobility that increases with decreasing temperature. Here transistors based on the polycyclic molecule Ph-BTBT-10, which crystallizes in domains that are hundreds of micrometers long, present mobility that is already high at room temperature and bandlike down to 80 K. This study demonstrates that four-probe measurements are essential to understanding intrinsic transport in these materials.

High spin polarization and the origin of unique ferromagnetic ground state in CuFeSb

CuFeSb is isostructural to the ferro-pnictide and chalcogenide superconductors and it is one of the few materials in the family that are known to stabilize in a ferromagnetic ground state. Majority of the members of this family are either superconductors or antiferromagnets. Therefore, CuFeSb may be used as an ideal source of spin polarized current in spin-transport devices involving pnictide and the chalcogenide superconductors. However, for that the Fermi surface of CuFeSb needs to be sufficiently spin polarized. In this paper we report direct measurement of transport spin polarization in CuFeSb by spin-resolved Andreev reflection spectroscopy. From a number of measurements using multiple superconducting tips we found that the intrinsic transport spin polarization in CuFeSb is high (∼47%). In order to understand the unique ground state of CuFeSb and the origin of large spin polarization at the Fermi level, we have evaluated the spin-polarized band structure of CuFeSb through first principles calculations. Apart from supporting the observed 47% transport spin polarization, such calculations also indicate that the Sb-Fe-Sb angles and the height of Sb from the Fe plane are strikingly different for CuFeSb than the equivalent parameters in other members of the same family thereby explaining the origin of the unique ground state of CuFeSb.

Enhanced Conductivity in the Metastable Intermediate in Li x FePO4 Electrode

Olivine LiFePO4 is a major commercial cathode material for lithium ion batteries due to its high specific theoretical capacity, low cost, nontoxicity, and superb thermal/chemical stability. In addition to the above properties, olivine LiFePO4 shows an exceptional high-rate capability despite its poor intrinsic electronic conductivity and sluggish two-phase reaction process. Last year, a non-equilibrium solid solution reaction process was experimentally demonstrated by Grey et al[1]. Independent research was conducted by several groups and confirmed these results[2] , [3]. Recently, we have determined the crystal structure of intermediate Li2/3FePO4 [4]. However, until now there has been no investigation on the transport properties of the metastable intermediate phase formed at the phase boundary interface during the non-equilibrium process due to the following extreme technical difficulties. First, the solid solution phase Li x FePO4 is metastable during electrochemical process and disappears within a few seconds after relaxation[1,3]. We overcame this limitation by quenching Li x FePO4 (x = 0.6) at 350 °C to room temperature. This quenched phase remained stable for a couple of weeks, which enabled sufficient time to measure the intrinsic conductivity. Second, conductive carbon may form during sintering at high temperature from possible carbon sources such as polyolefin worn from jars, organic solvent used in milling and carbon-containing precursors (e.g., oxalate FeC2O4·2H2O). Finally, impurities such as Li3PO4, Li4P2O7 and Fe x P resulting from off-stoichiometric mixing or the carbon reduction effect above 800 °C will largely increase the apparent conductivity of LiFePO4 by several orders of magnitude[5]. The scattering of the LiFePO4 conductivity data resulting from the above extrinsic effects has troubled and confused scientists for a long time. In our present study, pure carbon-free LiFePO4 and FePO4 were prepared using carbon-free precursors and controlling sintering parameters, and the intrinsic conductivity of quenched single phase Li x FePO4 (x = 0.6) was measured. The following figure shows representative Nyquist plots of carbon-free LiFePO4, carbon-free FePO4, and quenched Li0.6FePO4 samples measured at 340 K. Of particular interest is that the electronic resistance of the quenched single-phase Li0.6FePO4 was approximately 2 orders of magnitude smaller than those of the two end-members (LiFePO4 and FePO4) at 340 K. The temperature-dependent conductivity was also measured. Across the entire temperature range of 30 to 350 °C, the single-phase Li0.6FePO4 shows approximately 2 orders of magnitude superior electronic conductivity. The activation energy of Li0.6FePO4 obtained from the slope of the temperature-dependent conductivity was almost identical to the two end members (LiFePO4 and FePO4), which means that the enhanced electronic conductivity originates from the increased charge carrier density. In summary, a metastable solid solution phase Li x FePO4 (x = 0.6) was isolated by the optimized quenching protocol and found to have approximately 2 orders of magnitude enhanced electronic conductivity over the two end members of LiFePO4 and FePO4. Our research reveals that the single-phase transformation mechanism not only relaxes the interface strain energy but also enhances the intrinsic charge transport, enabling the high-rate capability of olivine LiFePO4.

Tunable Photoinduced Carrier Transport of a Black Phosphorus Transistor with Extended Stability Using a Light-Sensitized Encapsulated Layer

In this article, we propose a novel approach to demonstrate tunable photoinduced carrier transport of a few-layered black phosphorus (BP) field-effect transistor (FET) with extended air stability using a “light-sensitized ultrathin encapsulated layer”. Titanium suboxide (TiOx) ultrathin film (approximately 3 nm), which is an amorphous phase of crystalline TiO2 and can be solution processed, simultaneously exhibits the unique dual functions of passivation and photoinduced doping on a BP FET. The photoinduced electron transfer at TiOx/BP interfaces provides tunable n-type doping on BP through light illumination. Accordingly, the intrinsic hole-dominated transport of BP can be gradually tuned to the electron-dominated transport at a TiOx/BP FET using light modulation, with enhanced electron mobility and extended air stability of the device. The novel device structure consisting of a light-sensitized encapsulated layer with controllable and reversible doping through light illumination on BP exhibits great pot...

Electronic spin transport in dual-gated bilayer graphene

The elimination of extrinsic sources of spin relaxation is key in realizing the exceptional intrinsic spin transport performance of graphene. Towards this, we study charge and spin transport in bilayer graphene-based spin valve devices fabricated in a new device architecture which allows us to make a comparative study by separately investigating the roles of substrate and polymer residues on spin relaxation. First, the comparison between spin valves fabricated on SiO2 and BN substrates suggests that substrate-related charged impurities, phonons and roughness do not limit the spin transport in current devices. Next, the observation of a 5-fold enhancement in spin relaxation time in the encapsulated device highlights the significance of polymer residues on spin relaxation. We observe a spin relaxation length of ~ 10 um in the encapsulated bilayer with a charge mobility of 24000 cm2/Vs. The carrier density dependence of spin relaxation time has two distinct regimes; n<4 x 1012 cm-2, where spin relaxation time decreases monotonically as carrier concentration increases, and n>4 x 1012 cm-2, where spin relaxation time exhibits a sudden increase. The sudden increase in the spin relaxation time with no corresponding signature in the charge transport suggests the presence of a magnetic resonance close to the charge neutrality point. We also demonstrate, for the first time, spin transport across bipolar p-n junctions in our dual-gated device architecture that fully integrates a sequence of encapsulated regions in its design. At low temperatures, strong suppression of the spin signal was observed while a transport gap was induced, which is interpreted as a novel manifestation of impedance mismatch within the spin channel.

Intrinsic Charge Transport across Phase Transitions in Hybrid Organo-Inorganic Perovskites.

Hall effect measurements in CH3 NH3 PbBr3 single crystals reveal that the charge-carrier mobility follows an inverse-temperature power-law dependence, μ ∝ T(-) (γ) , with the power exponent γ = 1.4 ± 0.1 in the cubic phase, indicating an acoustic-phonon-dominated carrier scattering, and γ = 0.5 ± 0.1 in the tetragonal phase, suggesting another dominant mechanism, such as a piezoelectric or space-charge scattering.