Device simulation of carrier transport through grain. Grain boundaries in low molar mass p3ht have been shown to be detrimental to charge carrier mobility 25. Summary hall mobility is used to characterize the microscopic quality of semiconductors. 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. Carrier transport across grain boundaries in polycrystalline. Carriers and current in semiconductors 2 carrier transport two driving forces for carrier transport. Both driving forces lead to a directional motion of carriers superimposed on the random thermal motion. Conversely to analytical models based on the wentzelkramersbrillouin wkb approximation, our new approach is valid for any doping level. Although amorphous materials lack grain boundaries and periodicity, the electron transport is more complex than in the crystalline phases. Studies of band structure and free carrier scattering in. Identifying defecttolerant semiconductors with high minority. 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. Effect of dislocation arrays at grain boundaries on. Studies of the influence, and its control, of grain.
Anomalous grain boundary physics in polycrystalline cuinse2. Current studies of the carrier transport mechanisms in halfheusler compounds mainly focus on acoustic phonons, alloy and grain boundary scatterings. Both confocal and widefield images show that carriers undergo anisotropic diffusion due to differences in intergrain connectivity. Temperatureactivated charge transport in disordered organic semiconductors at large carrier concentrations, especially relevant in organic fieldeffect transistors ofets, has been thoroughly considered using a recently developed analytical formalism assuming a gaussian densityofstates dos distribution and millerabrahams jump rates.
Isolated grain boundaries are formed by vacuum deposition of pairs of 6t grains between au electrodes 1. Electrical properties of grain boundaries in polycrystalline. Several experimental and computational techniques now show that the. Energy barriers at grain boundaries dominate charge carrier transport in an electronconductive organic semiconductor. Studies of the influence, and its control, of grain boundaries on minoritycarrier transport in polysilicon devices by. Charge carrier transport along grain boundaries in silicon. Energy barriers at grain boundaries dominate charge carrier. 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. 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. Ravindran, phy02e semiconductor physics, 21 february 20. At the same time, electrostaticgated homojunctions enable the hot carriermediated photothermoelectric pte effect in graphene 58. Carrier transport at grain boundaries is described as it has been developed from the studies on germanium and iiivcompound bicrystals.
A generalized model of carrier transport in polycrystalline materials was proposed by seto 16 and later extended by baccarani et al. 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. 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. A unified approach to current transport across a grain boundary in polycrystalline semiconductors is developed. 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. 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. Electrical transport is affected by film thickness in metallic and semiconductor. The electrical transport properties of these materials differ dramatically from monocrystalline materials due to the presence of grain boundaries.
In this dissertation we develop an analytic model for minority carrier transport in polysilicon devices, and provide experimental corroboration for the model. Energy barriers at grain boundaries dominate charge carrier transport in an electronconductive organic semiconductor article pdf available in scientific reports 81. The nonequilibrium transport persisted over tens of picoseconds and 600 nanometers before reaching the diffusive transport limit. Dynamics of carrier transport in nanoscale materials. Electrical transport between singlecrystal domains could be affected by scattering at the grain boundary gb, as has been shown theoretically 69. 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. Carrier transport at grain boundaries is described as it has been developed from the studies on germanium and iii. Pdf energy barriers at grain boundaries dominate charge carrier. Intrinsic carrier concentrations recall that we can also find the dependence on temperature for intrinsic semiconductors, we know the following. Large modulation of carrier transport by grainboundary. Analytical modelling of carrier transport through transverse. 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.
The model is used to facilitate the development of experimental techniques, compatible with conventional device. The study concentrates on the carrier trapping effect, and the trappingstate density can. The impact of the dielectric semiconductor interface on. Afm images comparing microstructure of pbttt on ots a and oxide b. Understanding the atomic structures of grain boundaries gbs is essential to controlling and improving electrical transport properties in both bulk and lowdimensional materials. Thus, the role of interfaces grain boundaries may be important. Jul 16, 2001 temperature and gate voltage dependent transport measurements on single grain boundaries in the organic semiconductor sexithiophene 6t are described. Tailoring electrical transport across grain boundaries in. These are primarily the effective mass and the nature of carrier scattering processes. The model considers an array of square grains in the channel of polysi tft in which current flows along the longitudinal gbs. Brown boueri research center, ck5405 baden, switzerland. Ballistic carrier transport in semiconductors studied by ultrafast laser techniques by lalani k. Grain boundaries are already known to have a large effect on the charge carrier mobility of molecular semiconductors. Grain boundaries limit the charge carrier transport in.
What is common to both worlds of interest is the physical background of the electrically active grain boundaries. The nonequilibrium transport persisted over tens of picoseconds and 600 nanometers before reaching the. Carrier transport through transverse and longitudinal grain boundaries gbs in polysilicon thin film transistors polysi tfts has been studied. Temperature and gate voltage dependent transport measurements on single grain boundaries in the organic semiconductor sexithiophene 6t are described. In section 2, we discuss the electronic properties that determine carrier mobility and affect the optical transmittance. In the third section, we discuss a novel method to measure. 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.
An accurate comparison between experimental carrier mobility and theoretical calculation is of great importa. Temperature and gate voltage dependent transport across a. Microscopic origin for electrically benign smallangle grain. Electron tunneling through grain boundaries in transparent. 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. For instance, edges and grain boundaries in graphene samples have been used to control surface plasmons 24. Important features are lateral blocking layers, longitudinal or sheet conduction, spacecharge extension with lateral bias, recombination and photovoltaic effects. This leads to a relationship between the mobility and the diffusion constant called the einstein relation. Electronic transport in semiconductor materials springerlink. Carrier transport at grain boundaries 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. 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. In addition, trts reveals electronhole charge carrier mobilities of up to 0.
Measurement and calculation of the carrier concentration in. Here we present an investigation of carrier diffusion through polycdte using a novel photoluminescence pl imaging technique. Grainboundarylimited transport in semiconducting sno2 thin. Pdf energy barriers at grain boundaries dominate charge. In traditional mesoscopic semiconductors, gbs are scattering sites for majority carriers and degrade transport via the formation of electrostatic barriers 1, 2. Tracking photoexcited carriers in hybrid perovskite. Applied physics copyright 2019 asymmetric hotcarrier. Accelerated carrier recombination by grain boundaryedge. Studies of the influence, and its control, of grain boundaries on minority carrier transport in polysilicon devices by. 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. Pdf temperature dependence of the charge carrier mobility. The influence of gbs contained in the channel of mosfets fabricated in thin soi layers is demonstrated.
Quasiballistic transport was observed to correlate with excess kinetic energy, resulting in up to 230 nanometers transport distance that could overcome grain boundaries. A polycrystalline material 2 is made of small crystallites joined at their surfaces via grain boundaries gbs. 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. Polycrystalline semiconductors are already widely used in integrated circuits and. Carrier transport through grain boundaries in lightly doped polysilicon. Ito films show much lower trap densities down to n t. 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. Details studies of the influence, and its control, of 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. 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. Establishing the carrier scattering phase diagram for zrnisn. An additional degree of freedom is given by vertical heterostructure assembly 9.
Carriers concentration and current in semiconductors. A conduction model for semiconductorgrain boundary. These interfaces tend to become sinks for both chemical impurities and structural defects that segregate there from the grain interior gi during growth. Card columbia radiation laboratory and department of electrical engineering, columbia university, ny 10027, u. Carrier recombination at grain boundaries and the effective. A schematic view for such carrier transport is shown in figure 2. Measuring longrange carrier diffusion across multiple grains. One parameter to assess the quality of charge transport in organic semiconductors is the charge carrier mobility of electrons or holes. The carrier transport mechanisms underlying their high te performance has been a focus of study. We established a model for investigating polycrystalline silicon polysi thin film transistors tfts.
Oct 25, 20 a generalized model of carrier transport in polycrystalline materials was proposed by seto 16 and later extended by baccarani et al. Intergrain boundaries in a polycrystalline film will act to scatter the carriers being. Carrier transport through grain boundaries in semiconductors. Important features are lateral blocking layers, longitudinal or sheet conduction, space.
Carrier transport through grainboundaries in semiconductors. The importance of organic singlecrystal research stems from several speci. Both carrier transport mechanisms are related since the same particles and scattering mechanisms are involved. 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. 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. Request pdf on researchgate carrier transport through grain boundaries in semiconductors the transport of majority carriers through an electrically active.