Pdf energy barriers at grain boundaries dominate charge. Grain boundaries limit the charge carrier transport in. Grain boundaries in low molar mass p3ht have been shown to be detrimental to charge carrier mobility 25. Microscopic origin for electrically benign smallangle grain. Grain boundary diffusion coefficients are generally measured in the socalled typeb kinetics region harrison 1961 where vd l t d l is the lattice diffusion coefficient and t is the time is comparable to the spacing between grain boundaries, i. Grainboundarylimited transport in semiconducting sno2 thin. Analytical modelling of carrier transport through transverse. Electron tunneling through grain boundaries in transparent. Dynamics of carrier transport in nanoscale materials. The nonequilibrium transport persisted over tens of picoseconds and 600 nanometers before reaching the diffusive transport limit. Tracking photoexcited carriers in hybrid perovskite. The influence of gbs contained in the channel of mosfets fabricated in thin soi layers is demonstrated. For instance, edges and grain boundaries in graphene samples have been used to control surface plasmons 24.
Anomalous grain boundary physics in polycrystalline cuinse2. These data are all qualitatively consistent with trapdominated variations in local photoluminescence intensity and with grain boundaries that exhibit varying degrees of opacity to carrier transport. Request pdf on researchgate carrier transport through grain boundaries in semiconductors the transport of majority carriers through an electrically active. We thus provide a complete model that allows a comprehensive explanation of carrier transport in highly doped semiconductors, for which charge tunneling across grain boundaries cannot be neglected. Ballistic carrier transport in semiconductors studied by ultrafast laser techniques by lalani k. Carrier transport through transverse and longitudinal grain boundaries gbs in polysilicon thin film transistors polysi tfts has been studied. Brown boueri research center, ck5405 baden, switzerland. In addition, trts reveals electronhole charge carrier mobilities of up to 0. A unified approach to current transport across a grain boundary in polycrystalline semiconductors is developed.
A generalized model of carrier transport in polycrystalline materials was proposed by seto 16 and later extended by baccarani et al. Summary hall mobility is used to characterize the microscopic quality of semiconductors. Ito films show much lower trap densities down to n t. Several experimental and computational techniques now show that the. In traditional mesoscopic semiconductors, gbs are scattering sites for majority carriers and degrade transport via the formation of electrostatic barriers 1, 2. Both confocal and widefield images show that carriers undergo anisotropic diffusion due to differences in intergrain connectivity. At the same time, electrostaticgated homojunctions enable the hot carriermediated photothermoelectric pte effect in graphene 58. Misorientationangledependent electrical transport across. Effect of dislocation arrays at grain boundaries on.
The model is used to facilitate the development of experimental techniques, compatible with conventional device. Carriers and current in semiconductors 2 carrier transport two driving forces for carrier transport. Applied physics copyright 2019 asymmetric hotcarrier. Werake submitted to the graduate degree program in physics and astronomy and the faculty of the graduate school of the university of kansas in partial fulfillment of the requirements for the degree of doctor of philosophy.
Defect, grain boundaryedge, carrier recombination, mbe, transition metal dichalcogenides. As electrically benign, lowcost, nearsinglecrystalline semiconductors is crucial for largescale applications, understanding the electrical behavior of smallangle grainboundaries gbs, consisting of array of dislocations, becomes important. Details studies of the influence, and its control, of grain. Intergrain boundaries in a polycrystalline film will act to scatter the carriers being. Tailoring electrical transport across grain boundaries in. The impact of the dielectric semiconductor interface on. Pdf temperature dependence of the charge carrier mobility. In this dissertation we develop an analytic model for minority carrier transport in polysilicon devices, and provide experimental corroboration for the model.
Although amorphous materials lack grain boundaries and periodicity, the electron transport is more complex than in the crystalline phases. Energy barriers at grain boundaries dominate charge carrier. The model considers an array of square grains in the channel of polysi tft in which current flows along the longitudinal gbs and through the grains and the transverse gbs. Carrier transport through grainboundaries in semiconductors. Grain boundaries in materials can act as interfaces to scatter phonons,6 electrical traps for charge carriers,6769 and segregation sites for dopant atoms. We established a model for investigating polycrystalline silicon polysi thin film transistors tfts. Ravindran, phy02e semiconductor physics, 21 february 20. An additional degree of freedom is given by vertical heterostructure assembly 9. Studies of band structure and free carrier scattering in. Grain boundary defects not only trap and reduce free carriers, but also form potential barriers and interfere with carrier movement. Introduction interest in grain boundaries in semiconductors has undergone a remarkable expansion.
Accelerated carrier recombination by grain boundaryedge. One parameter to assess the quality of charge transport in organic semiconductors is the charge carrier mobility of electrons or holes. The resulting expressions for potential barrier and jv characteristics are of general validity, in contrast to the many derivations of previous models, each with its own conditions of validity. Important features are lateral blocking layers, longitudinal or sheet conduction, space. Device simulation of carrier transport through grain. The drain current measured at room temperature increases about 50 times for nfets and about 10 times for pfets, respectively, as compared to reference devices. Large modulation of carrier transport by grainboundary. Measurement and calculation of the carrier concentration in. Herein, it is verified that the localized dislocation arrays at grain boundaries enable the suppression of minority carrier contribution to electronic transport properties, resulting in an increase of the seebeck coefficient and the carrier mobility in bismuth antimony tellurides. A schematic view for such carrier transport is shown in figure 2.
Pdf energy barriers at grain boundaries dominate charge carrier. Electrical transport is affected by film thickness in metallic and semiconductor. This leads to a relationship between the mobility and the diffusion constant called the einstein relation. Although tem has provided a fast and accurate means to identify and image the structure of gbs in cvd graphene, the electrical impact of gbs has so far been studied only indirectly in experiments. A complimentary analysis by timeresolved terahertz spectroscopy trts shows that this improvement can be assigned to an increase of the grain size in the heattreated films.
Conversely to analytical models based on the wentzelkramersbrillouin wkb approximation, our new approach is valid for any doping level. Carrier transport at grain boundaries is described as it has been developed from the studies on germanium and iii. Intrinsic carrier concentrations recall that we can also find the dependence on temperature for intrinsic semiconductors, we know the following. Oct 25, 20 a generalized model of carrier transport in polycrystalline materials was proposed by seto 16 and later extended by baccarani et al. Both carrier transport mechanisms are related since the same particles and scattering mechanisms are involved. Temperature and gate voltage dependent transport across a. The model considers an array of square grains in the channel of polysi tft in which current flows along the longitudinal gbs. An accurate comparison between experimental carrier mobility and theoretical calculation is of great importa. Temperature and gate voltage dependent transport measurements on single grain boundaries in the organic semiconductor sexithiophene 6t are described. Carrier transport through grain boundaries in lightly doped polysilicon. The electrical transport properties of these materials differ dramatically from monocrystalline materials due to the presence of grain boundaries. Carrier transport at grain boundaries in semiconductors. Charge carrier transport along grain boundaries in silicon. As described above, the effective barrier height at the grain boundaries e b which in this model corresponds to e a depends on the density of grain boundaries and the charge carrier density.
Diffusion at semiconductor grain boundaries is also discussed, and finally the electrical properties of zinc oxide varistor material are presented in the light of the models of carrier interactions with grain boundaries 1. Carrier transport across grain boundaries in polycrystalline. These are primarily the effective mass and the nature of carrier scattering processes. Carriers concentration and current in semiconductors. Carrier transport through grain boundaries in semiconductors.
Carrier transport at grain boundaries is described as it has been developed from the studies on germanium and iiivcompound bicrystals. Jul 16, 2001 temperature and gate voltage dependent transport measurements on single grain boundaries in the organic semiconductor sexithiophene 6t are described. Establishing the carrier scattering phase diagram for zrnisn. Quasiballistic transport was observed to correlate with excess kinetic energy, resulting in up to 230 nanometers transport distance that could overcome grain boundaries. These interfaces tend to become sinks for both chemical impurities and structural defects that segregate there from the grain interior gi during growth. The study concentrates on the carrier trapping effect, and the trappingstate density can.
A repulsive electrostatic potential at the grain boundaries locally reduces the carrier density, hence the magnitude of the effective mobility is an underestimate of the true carrier mobility in the barrier region. Tuning charge transport in solutionsheared organic. In section 2, we discuss the electronic properties that determine carrier mobility and affect the optical transmittance. Both driving forces lead to a directional motion of carriers superimposed on the random thermal motion. Here we present an investigation of carrier diffusion through polycdte using a novel photoluminescence pl imaging technique. Current studies of the carrier transport mechanisms in halfheusler compounds mainly focus on acoustic phonons, alloy and grain boundary scatterings. Establishing a detailed and accurate account of the relationship between grain boundaries, impurities and carrier transport in polycrystalline semiconductors requires a direct method of probing carrier diffusion paths. Isolated grain boundaries are formed by vacuum deposition of pairs of 6t grains between au electrodes 1. Energy barriers at grain boundaries dominate charge carrier transport in an electronconductive organic semiconductor. Thus, the role of interfaces grain boundaries may be important. Studies of the influence, and its control, of grain boundaries on minoritycarrier transport in polysilicon devices by. A polycrystalline material 2 is made of small crystallites joined at their surfaces via grain boundaries gbs.
Electrical transport between singlecrystal domains could be affected by scattering at the grain boundary gb, as has been shown theoretically 69. The effect of grain boundaries gbs on the transfer characteristics of tft was analyzed by considering the number and the width of grain boundaries in the channel region, and the dominant transport mechanism of carrier across grain boundaries was subsequently determined. Electronic transport in semiconductor materials springerlink. Card columbia radiation laboratory and department of electrical engineering, columbia university, ny 10027, u. The nonequilibrium transport persisted over tens of picoseconds and 600 nanometers before reaching the. The transport of majority carriers through an electrically active grain boundary is treated for the situation where deep traps are an essential feature of the bulk semiconductor. A conduction model for semiconductorgrain boundary. What is common to both worlds of interest is the physical background of the electrically active grain boundaries. Afm images comparing microstructure of pbttt on ots a and oxide b. In the third section, we discuss a novel method to measure.
Electrons trapped at the interface are screened by the ionized defect states within the depletion regions and thereby a double schottky potential barrier is formed. Important features are lateral blocking layers, longitudinal or sheet conduction, spacecharge extension with lateral bias, recombination and photovoltaic effects. Understanding the atomic structures of grain boundaries gbs is essential to controlling and improving electrical transport properties in both bulk and lowdimensional materials. Measuring longrange carrier diffusion across multiple grains. Energy barriers at grain boundaries dominate charge carrier transport in an electronconductive organic semiconductor article pdf available in scientific reports 81. Identifying defecttolerant semiconductors with high minority. The importance of organic singlecrystal research stems from several speci.
The possibility of achieving low carrier densities, the purity and perfection of single crystals, low effective carrier masses, and high dielectric constants have established semiconductors as exceedingly versatile in contrast to metals for understanding and utilizing electronic. Studies of the influence, and its control, of grain boundaries on minority carrier transport in polysilicon devices by. Polycrystalline semiconductors are already widely used in integrated circuits and. The carrier transport mechanisms underlying their high te performance has been a focus of study. Electrical properties of grain boundaries in polycrystalline.