Annealing effects on aluminum/hydrogenated amorphous silicon (a‐Si:H) contacts in the temperature range from 100 to 300 °C were studied. Al was evaporated on device‐quality, phosphorus‐doped (n+) a‐Si:H films deposited in a UHV plasma‐enhanced chemical‐ vapor‐deposition system. Both electrical measurements and surface morphological analyses were performed to characterize the interaction. The transmission line model technique was used to measure sheet resistance and contact resistivity. For samples where Al covered the entire a‐Si:H surface during annealing, sheet resistance and contact resistivity were found to decrease monotonically with annealing temperature; whereas, samples annealed after patterning of the Al pads exhibited a minimum in sheet resistance and contact resistivity at temperatures between 150 and 200 °C. Optical and scanning electron microscopy, surface profilometry, and Raman spectroscopy were used to study the surface morphology. Interaction of Al with a‐Si:H was observed to initiate at ...

Interaction of aluminum with hydrogenated amorphous silicon at low temperatures

In this letter, we investigated the effects of source/drain series resistance on amorphous gallium-indium-doped zinc-oxide (a-GIZO) thin film transistors (TFTs). A linear least square fit of a plot of the reciprocal of channel resistance versus gate voltage yields a threshold voltage of 3.5 V and a field-effect mobility of about 13.5 cm2/Vldrs. Furthermore, in a-GIZO TFTs, most of the current flows in the distance range of 0-0.5 mum from the channel edge and shorter than that in a-Si:H TFTs. Moreover, unlike a-Si:H TFTs, a-GIZO TFTs did not show an intersection point, because they did not contain a highly doped ohmic (n+) layer below the source/drain electrodes.

Source/Drain Series-Resistance Effects in Amorphous Gallium–Indium Zinc-Oxide Thin Film Transistors

The reaction between hydrogenated amorphous silicon (a‐Si:H) film and aluminum has been investigated by Transmission Electron Microscopy and Scanning Electron Microscopy (SEM). The formation of aluminum silicide was observed even at room temperature. Subsequent annealing of the sample showed [111], [110] and [311] orientations of aluminum silicide coexisting as revealed by the electron diffraction patterns. This silicide has a bcc structure with lattice parameter of 6.36 A. The precipitation of Si at the interface was observed in SEM after selective etching of Al from the top surface of the sample. The silicide disappears completely at 300 °C with the formation of polycrystalline and porous silicon. The effect of temperature related structural changes on the electrical properties of Al/a‐Si:H Schottky diode has also been studied.

Silicide mediated low temperature crystallization of hydrogenated amorphous silicon in contact with aluminum

We calculated a more accurate density of states (DOS) profile from field‐effect (FE) measurements in hydrogenated amorphous silicon thin‐film transistors, taking into account the anomalously changing conductivity prefactor in accordance with the Meyer–Neldel (MN) rule. We present a self‐consistent analysis of the density of gap states profile, where the MN rule is, for the first time, properly considered in relation to the nonuniform shift of the Fermi level as induced by the field effect. Moreover, the calculation yields the correct flat‐band voltage and the corresponding flat‐band activation energy. The determination of conductivity activation energies free from any initial band bending effects is of importance in all types of transport measurements.

/pdf/a-self-consistent-analysis-of-temperature-dependent-field-1w5mb9qcts.pdf

A self-consistent analysis of temperature-dependent field-effect measurements in hydrogenated amorphous-silicon thin-film transistors

Measurements are reported on x‐ray diffraction and Auger electron spectroscopy studies of Al films on phosphorous‐doped hydrogenated amorphous silicon (a‐Si:H) prepared by rf glow discharge deposition. Infrared absorption and current‐voltage characteristics of and Al electrode a‐Si:H p‐i‐n diodes are also presented. Si and Al Auger depth profile data show that Si was detected at the free surface of the 5000‐A Al film on the 1500‐A a‐Si:H film after a 185 °C anneal, while a constant Si signal was detected in the Al film from its free surface to the interface with the a‐Si:H after a 200 °C anneal. The 200 °C anneal reduced the p‐i‐n diodes to resistors. The a‐Si‐H in contact with the Al film crystallized at 300 °C. A 360 °C anneal prior to the Al deposition raised the recrystallization temperature above 300 °C. The evolution of hydrogen is proposed as a mechanism for lowering the recrystallization temperature in a–Si:H.

Low‐temperature crystallization of hydrogenated amorphous silicon films in contact with evaporated aluminum electrodes

Amorphous silicon thin-film field-effect transistors have been made with a staggered electrode structure. In this structure we distinguish two separate contributions to the total contact resistance, namely, the Al/a-Si:H barrier itself and the bulk resistance of the underlying a-Si:H layer. Concerning the first contribution it was found that a P-implantation forming n+regions followed by post-metallization annealing (PMA) at a moderate temperature of 200°C is very efficient in reducing the resistance of the Al contacts to negligibly small values. The second contribution, i.e., the bulk resistance, implies a variable series resistance in field-effect (FE) measurements. Thin-film transistors (TFT's) with different gate lengths were used for the first time to determine this residual series resistance R res .

J.W.C. Veltkamp

Papers

On the quality of contacts in a-Si:H staggered electrode thin-film transistors