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Amorphous & Polymorphous Silicon


For information on internships, doctoral studies, post-doctoral positions, or collaborations, please contact Prof. Pere Roca i Cabarrocas

Nanocrystalline Silicon

Microcrystalline (µc-Si:H) or nanocrystalline silicon is a complex but crucial material for modern and future thin-film electronics applications.  The technological ability to grow films of silicon at low temperatures (<250°C) that contain crystalline domains of tens to hundreds of nanometers in size reveals both great challenges in understanding to accompany the superior electronic properties of this material system.


Cross sectional HR-TEM Image of µc-Si:H thin film
The LPICM has a number of activities focussing on the growth of µc-Si:H silicon by PECVD, focussing on deposition by novel plasma generation techniques, new µcSixC1-x:H alloys, and new characterization techniques to understand the fundamentals of microcrystalline silicon growth and the dynamics of the devices fabricated thereof.
  •  Novel Plasma Generation Techniques for Microcrystalline Silicon

 The LPICM has at its disposal a wide range of plasma-based deposition techniques for thin films: standard RF-PECVD equipment, microwave frequency excited Plasmas (Matrix Distributed Electron Cyclotron Resonance and Microwave Loop Antenna systems), and Tailored Voltage Waveform deposition. All of these techniques are being explored in various forms to the deposition of µc-Si:H

 


 

For information on this subject, please consult the Plasma Processes section of this website.

  • New µc-SixC1-x:H Alloys
The fundamental instability of a-Si:H under light-soaking has led researchers to pursue alternative materials to satisfy the requirements of a top cell in thin film silicon photovoltaic tandem devices.  As a potential response to this need, we are investigating µc-SixC1-x:H alloys to provide the wider gap and stability required.  As part of the ANR-CANASTA project, we are applying the wide range of plasma processing techniques available at the LPICM (see section on Plasma Processes) to the deposition of this material.

  • New Characterization Techniques
 Microcrystalline silicon is a material that is notoriously sensitive to deposition conditions, particularly at high deposition rates.  A technique that has been developed to detect material that is prone to post-oxidation is the observation of specific peaks in the FTIR spectrum (Smets et al.)

For information on internships, doctoral studies, post-doctoral positions, or collaborations, please contact Dr. Erik Johnson

Epitaxy at 200°C


For information on internships, doctoral studies, post-doctoral positions, or collaborations, please contact Prof. Pere Roca i Cabarrocas


Silicon Nanowires

Research topics and motivations:

1D silicon nanowires (SiNWs) are widely recognized as essentail building blocks for new generations of high-efficiency solar cells as well as high mobility field effect transistors. At LPICM we focus on producing silicon nanowires in a cost-efficient and CMOS-compatible approach. We emphasize the ability of in-situ fabrication and integration of SiNW based devices  in a conventional plasma enhanced chemical vapor deposition (PECVD) system.  

 

Two distinctive growth strategies of SiNW growth are pursued:

à Vertical SiNWs produced via a plasma-assisted vapor-liquid-solid (VLS) growth mode, catalyzed by low melting-temperature catalysts (tin and indium), aiming for SiNW radial junction solar cells or photonic applications; à Lateral SiNWs produced via a newly discovered in-plane solid-liquid-solid (IPSLS) growth mode for large-scale implementation of growth-in-place SiNW thin film transistors, and sensors, in a fully compatible CMOS process.    

  • Related research interests

1. Developing new understanding and insight into the growth mechanism and kinetic behavior, for achieving effective morphology, structure and position control.

2. Growth and morphology control of related semiconductor nanowires, as well as epitaxial hetero-junction structure. 


For information on internships, doctoral studies, post-doctoral positions, or collaborations, please contact Dr Linwei YU


Dielectrics

Dielectric thin films are used in a large variety of applications such as gate dielectrics in MOS transistors, anti-scratch layers, optical filters and passive components for optoelectronics (waveguides, for example). Typically we grow silicon alloys of different compositions (oxides, nitrides and oxinitrides) that are generally transparent in the visible wavelengths range. Those materials are all deposited by Plasma Enhanced Chemical Vapor Deposition.



Figure 1.         MDECR plasma Ar discharge in the  deposition chamber

 

 Our Dielectric Thin Films are deposited by microwave (2.45 GHz) excited Plasma Enhanced Chemical Vapor Deposition. We combine the microwave excitation with a static magnetic field, which has the benefits of producing denser plasmas and confining the energetic electrons in the discharge. Indeed, the electrons are accelerated by the microwave electric field but also turned by the Lorentz force associated with the magnetic field. At a frequency of 2.45 GHz, a magnetic field strength of 875 Gauss ensures the optimal coupling between the electric and magnetic fields. This effect is known as Electron Cyclotron Resonance (ECR). In the deposition system, the magnet-antenna structures are distributed in space matrix-like, thus the nomenclature MDECR. Credit for the invention of such arrangement belongs to the French plasma physicist Dr. Jacques Pelletier from Grenoble.

 

The electronic density in the MDECR plasma can be up to 2 orders of magnitude higher that in the case of RF CCP plasmas (RF inductively coupled plasma produce comparable plasma density), and consequently, the dissociation of the precursor gas is very high. Therefore, very high deposition rates may be obtained (12nm/s for good quality SiO2). Another consequence is that in this kind of plasma, large ion flux can be obtained without external substrate bias, which allows us to obtain very dense, bulk-like, films. This is true also for room temperature depositions, which makes the deposition of Dielectric Thin Films on plastic possible.

 

Figure 2.         Bragg reflector on 2x2 inch Corning glass

 

Figure 3.         Design and measured transmission for Bragg reflector shown above

 

This research has been developed in a close collaboration with industry: L'Air Liquide in the period 1992-2001, with Saint Gobain Sekurit 1997-2001, with American company OCLI from the group JDS-Uniphase (2001-2002) and finally with Stec Inc. of Japanese Horiba Group (2002-2003). Recently, activity of dielectric deposition group was dedicated to in-situ process control studies in continuous collaboration with Jobin-Yvon Horiba Group and in-depth research of HDP-PECVD mechanisms including modeling activities and development of new distributed plasma source for High Density ECR-PECVD.

 

 

Figure 4.         MDECR-PECVD deposition chamber equipped with Jobin-Yvon Horiba UVISEL in-situ spectroscopic ellipsometer

 

For information on internships, doctoral studies, post-doctoral positions, or collaborations, please contact Dr. Pavel Bulkin