Directly deposited nanocrystalline silicon thin-film transistors with ultra high mobilities

Abstract

The authors report ultrahigh mobility nanocrystalline silicon thin-film transistors directly deposited by radio-frequency plasma enhanced chemical vapor deposition at 150°C. The transistors show maximum effective field effect mobilities of 450cm2∕Vs for electrons and 100cm2∕Vs for holes at room temperature. The authors argue that the key factor in their results is the reduction of the oxygen content, which acts as an accidental donor.

Influence of the statistical shift of Fermi level on the conductivity behavior in microcrystalline silicon

“…In spite of the immense potential of high efficiencies and large area deposition capabilities shown by µc-Si:H in semiconductor technology, especially in photovoltaics 24,25 and TFTs, 26 the understanding of its transport properties is impeded by these lacunae. Different conduction mechanisms and paths have been invoked to explain the electrical transport behavior in µc-Si:H, deriving information that correlate only some microstructural features and mechanisms.…”

Spatio-temporal pattern recognition in neural circuits with memory-transistor-driven memristive synapses

“…They are then connected into the spiking neuron circuit configuration shown in Figure 2, which is a modified version of that originally proposed by Mead [24]. Previous work used models of similar ambipolar devices to show the potential for their use in neuron circuits [25], [26]. However, the device models and subsequent neuron circuit behavior were also verified through fabrication and testing [27].…”

Input silane concentration effect on the a-Si:H to μc-Si:H transition width

“…Used as a photoactive material, it can be integrated as bottom cell in a tandem structure with an amorphous silicon top cell, lifting efficiencies of micromorph cells well above 10 % [2]. Used as carrier channel in thin film field effect transistors, it increases by several orders of magnitude the carrier mobility compared to amorphous silicon [3]. The properties of the microcrystalline material change depending on the specific application: in photovoltaics the amorphous matrix plays an important and not yet fully understood role of passivating grain boundaries and reducing defect densities [1,4].…”

“…The properties of the microcrystalline material change depending on the specific application: in photovoltaics the amorphous matrix plays an important and not yet fully understood role of passivating grain boundaries and reducing defect densities [1,4]. The best material is obtained within the transition region from amorphous to highly microcrystalline and knowledge of the variation of the crystalline fraction with respect to input silane concentration or any other process parameter like the RF power is thus critical; in thin film transistor technology instead, materials with higher crystallinity fractions are used, because of the larger carrier mobility [3]. Yet even if the required characteristics of the microcrystalline material are known for a specific application, the parameters in which microcrystalline silicon is deposited may vary considerably depending on such parameters as RF driving frequency [5], silane concentration in hydrogen [6] or the deposition rate [7].…”