Structural and electronic properties of dual plasma codeposited mixed-phase amorphous/nanocrystalline thin films

Abstract

A dual-plasma codeposition system capable of synthesizing thin films of mixed-phase materials consisting of nanoparticles of one type of material embedded within a thin film semiconductor or insulator matrix is described. This codeposition process is illustrated by the growth of hydrogenated amorphous silicon ͑a-Si:H͒ films containing silicon nanocrystalline inclusions ͑a/nc-Si:H͒. A capacitively coupled flow-through plasma reactor is used to generate silicon nanocrystallites of diameter 5 nm, which are entrained by a carrier gas and introduced into a capacitively coupled plasma enhanced chemical vapor deposition reactor with parallel plate electrodes, in which a-Si:H is synthesized. The structural and electronic properties of these mixed-phase a/nc-Si:H films are investigated as a function of the silicon nanocrystal concentration. At a moderate concentration ͑crystalline fraction 0.02-0.04͒ of silicon nanocrystallites, the dark conductivity is enhanced by up to several orders of magnitude compared to mixed-phase films with either lower or higher densities of nanoparticle inclusions. These results are interpreted in terms of a model whereby in films with a low nanocrystal concentration, conduction is influenced by charges donated into the a-Si:H film by the inclusions, while at high nanocrystal densities electronic transport is affected by increased disorder introduced by the nanoparticles.

Evaluation of 1/f noise in prospective IR imaging thin films

“…As the film continues to grow the crystal fraction in the films increases, which should result in a decrease of resistivity. However, the observed inverse relation between crystal fraction and the resistivity has also been observed in other material systems such as Si:H [16]. Here the increase in resistivity with thickness has been attributed to the inclusion of voids due to shadowing effects surrounding the nanocrystalline material.…”

Opto-electronic properties of co-deposited mixed-phase hydrogenated amorphous/nanocrystalline silicon thin films

“…A typical residence time of 3 ms results in nanocrystallite formation with an average diameter of between 5-6 nm. Details of the nanocrystal diameter dependence on chamber gas pressure and plasma residence time have been published previously [11,12].…”

Dual reactor deposition of quantum confined nanocrystalline silicon

“…Silicon nanoparticles using this approach have been produced down to 2 nm, but the high temperature processing is not ideal for photovoltaic cells and transport through the oxide is limited. Another approach was developed by Adjallah et al where the silicon nanoparticle synthesis and amorphous silicon deposition was decoupled allowing for plasma synthesized silicon nanoparticles to be directly injected into an amorphous silicon plasma [5]. While the majority of their samples had less than 3% crystal fraction, they did achieve a crystal fraction as high as 19% [5].…”

“…Another approach was developed by Adjallah et al where the silicon nanoparticle synthesis and amorphous silicon deposition was decoupled allowing for plasma synthesized silicon nanoparticles to be directly injected into an amorphous silicon plasma [5]. While the majority of their samples had less than 3% crystal fraction, they did achieve a crystal fraction as high as 19% [5]. In this study, we demonstrate an approach for producing quantum confined nanocrystalline silicon with high crystal fractions that may allow for a material that could be used to surpass the Shockley Queisser single junction limitation.…”