We investigate the mechanism for Si dangling bond defect creation in amorphous silicon thin film transistors as a result of bias stress. We show that the rate of defect creation does not depend on the total hydrogen content or the type of hydrogen bonding in the amorphous silicon. However, the rate of defect creation does show a clear correlation with the Urbach energy and the intrinsic stress in the film. These important results support a localized model for defect creation, i.e., where a Si–Si bond breaks and a nearby H atom switches to stabilize the broken bond, as opposed to models involving the long-range diffusion of hydrogen. Our experimental results demonstrate the importance of optimizing the intrinsic stress in the films to obtain maximum stability and mobility. An important implication is that a deposition process where intrinsic stress can be independently controlled, such as an ion-energy controlled deposition should be beneficial, particularly for deposition temperatures below 300 °C.

Effects of surface micromesas on reverse leakage current in InGaN/GaN Schottky barriers J. Appl. Phys. 112, 044505 (2012) The influence of the Franz-Keldysh effect on the electron diffusion length in p-type GaN determined using the spectral photocurrent technique J. Appl. Phys. 112, 044501 (2012) Electron beam induced current in InSb-InAs nanowire type-III heterostructuresWe analyze the forward characteristics of a-Si:H nip and pin diodes. At low bias, a well-defined exponential region exists, described by a noninteger quality factor n between 1.2 and 1.7. With increasing temperature, the quality factor decreases. This behavior can be understood with a model based on electron and hole recombination in the i layer, which relates the temperature dependence of the quality factor to the distribution of localized states in the amorphous silicon.The predictions of the model are supported by numerical calculations in which the diode device equations are solved for a given distribution of localized states. The different ideality factors are due to different energy dependencies of the density of deep states in the i layer.

We have measured the bias dependence of the threshold voltage shift in a series of amorphous silicon-silicon nitride thin-film transistors, where the composition of the nitride is varied. There are two distinct instability mechanisms: a slow increase in the density of metastable fast states and charge trapping in slow states. State creation dominates at low fields and charge trapping dominates at higher fields. The state creation is found to be independent of the nitride composition, whereas the charge trapping depends strongly on the nitride composition. This is taken as good evidence that state creation takes place in the hydrogenated amorphous silicon (a-Si:H) layer, whereas the charge trapping takes place in the a-SiN:H. The metastable states are suggested to be Si dangling bonds in the a-Si:H, and the state creation process similar to the Staebler–Wronski effect. The confirmation of state creation in a thin-film transistor means that states can be created simply by populating conduction-band states in the undoped material. The slow states are also thought to be Si dangling bonds, but located in the silicon nitride matrix.

International audienceMicrocrystalline siliconthin films prepared by the layer-by-layer technique in a standard radio-frequency glow discharge reactor were used as the active layer of top-gate thin-film transistors(TFTs). Crystalline fractions above 90% were achieved for silicon films as thin as 40 nm and resulted in TFTs with smaller threshold voltages than amorphous siliconTFTs, but similar field effect mobilities of around 0.6 cm2/V s. The most striking property of these microcrystalline silicontransistors was their high electrical stability when submitted to bias-stress tests. We suggest that the excellent stability of these TFTs, prepared in a conventional plasma reactor, is due to the stability of the μc-Si:H films. These TFTs can be used in applications that require high stability for which a-Si:HTFTs cannot be used, such as multiplexed row and column drivers in flat-panel display applications, and active matrix addressing of polymer light-emitting diodes

We have developed a new way of making flexible, plastic active matrix displays using standard amorphous silicon TFT fabrication facilities. Using this technique we have made electrophoretic displays with three micron thick plastic a-Si TFT backpanes. We believe that these are the thinnest plastic displays ever made.