Joint research project

Germanium on silicon tunable sensors for visible and near infrared bands and explosive detectors based on germanium and carbon nanostructures.

Project leaders
Claudio Ferrari, Sevda Abdullayeva
AZERBAIJAN - ANAS - Azerbaijan National Academy of Sciences
CNR-ANAS 2016-2017
Engineering, ICT and technologies for energy and transportation
Thematic area
Engineering, ICT and technologies for energy and transportation
Status of the project
Report for renewal

Research proposal

1-Germanium on silicon tunable sensors
The first goal of this project is to develop a semiconductor voltage-tunable sensor for visible and near-infrared bands integrated on the same chip, fabricated using Germanium on Silicon technology with a novel design of light detecting. The realization of this simple device will allow in the future the preparation of an image sensor based on silicon with tunable sensitivity between visible and near infrared range for surveillance and security applications.
Multi-band imaging is a relatively new approach which combines spectroscopic and spatial information. It extracts more information with respect to the so-called panchromatic imaging, where pixels record only the total intensity of radiation.
This technique has several applications in chemistry, astronomy, biology, medicine and remote sensing (including military and security) [1].
Multi-band imagers are typically complex, expensive, bulky; they often require multiple exposures and extensive post-processing. It is only recently that research efforts have been devoted towards more compact and integrated solutions. Dual band for medium wavelength infrared (MWIR) and long wavelength infrared (LWIR) were previously proposed and demonstrated, with both independent and simultaneous detection and voltage tunability, using arrays of quantum well infrared detectors in III-V compound semiconductors [2]. Much less work has been done in the VIS-NIR bands. In these spectral ranges only NIR-enhanced silicon CCD or CMOS arrays [3] or VIS-enhanced InGaAs [4] have been fabricated with multi-band operation eventually obtained by filtering. As of today, VIS-NIR voltage tunable image sensors are not available. Even if there is a 4% lattice mismatch with respect to silicon the integration of germanium devices in the silicon platform is by far much easier that the integration of other direct band gap III-V compounds due to its non polar structure.

In the previous approved project we tried to prepare a germanium on silicon device suitable for the integration with a front end interface based on a silicon chip for digital read-out of data. The main failure of the project was due to the difficulty of doping at the same time germanium epitaxial layers and silicon substrate.
In the present project we propose a new approach based on dopant implantation, specifically by boron implantation on n doped Ge epilayer and silicon substrate according to the following scheme:
a) epitaxial growth of n-doped (doping level 1018 cm-3) germaium layers on n doped silicon substrates
b) selective etching to remove part of the germanium epilayers
c) boron implantation of germanium and silicon
d) annealing to recover the implantation damage
e) electrode deposition and formation of the back to back diodes that can be selectively activated by polarization to detect the visible or the near infrared bands.

2-Explosive detectors based on germanium and carbon nanostructures

Techniques to detect high-explosive materials, such as TNT (2,4,6-trinitrotoluene), RDX (cyclotrimethylene trinitramine), PETN (pentaerytritol tetranitrate) at traces levels in luggage, vehicles, mail, aircraft and soils are very necessary. The development of nanotechnology potentially provides a feasible solution for building small, highly sensitive and selective explosive detectors. Semiconducting nanowires can detect TNT down to a detection limit of ~1x10-6 ppt by surface functionalization with an electron-rich amino-silane which binds the electron-deficient explosive molecules of TNT through charge-transfer donor-acceptor interactions thus causing sharp changes in the conductance of the electrical-sensing nanoelements [5].

Functionalized single-walled carbon nanotubes (SWNT) are highly responsive to their physical and chemical environment. SWNT are unique among nanoscale sensor platforms in their ability to detect the adsorption of as few as a single molecule of an analyte [6]. Single-walled carbon nanotubes (SWNT) may be covalently functionalized with urea, thiourea, and squaramide. Carbon nanotube (CNT) based chemiresistors display promising performance in explosive sensing. CNT chemiresistors can be deposited between electrodes by evaporation or dispersions, or can be effectively drawn from compressed CNT solids.

Both these systems demonstrated a very high sensitivity in detecting explosives, in particular molecules on trinitrotoluene in air. In the present project we propose the preparation of doped germanium nanowires and of carbon nanotubes as a starting point for the realization of sensors with improved detection limit and selectivity to different types of explosives.

[1] P. Colarusso, L.H. Kidder, I.W. Levin, J.C Fraser, J.F. Arens, E.N. Lewis, "Infrared Spectroscopic Imaging: From Planetary to Cellular Systems ", Appl. Spectr., 52, 106, 1998.
[2] M.H Hostut, K. Kilic, S. Sakiroglu, Y. Ergun, I. Sokmen, "Voltage tunable Dual-band quantum well infrared photodetector for third generation thermal inaging", IEEE Phot. Technol. Lett. 23, 1370, 2011.
[3] B. Tsaur, C.K. Chen, J. Mattia "PtSi schottky-barrier focal plane arrays for multispectral imaging in ultraviolet, visible and infrared spectral bands", IEEE Electron Dev. Lett. 11, 162, 1990.
[4] M.H. Ettenberg, M.J. Lange, T. O'Grady, J.S. Vermaak, M.J. Cohen, G.H. Olsen, A room temperature 640x480 pixel near-infrared InGaAs focal plane array", Proc. SPIE, 4028, 201, 2000.
[5] A. Lichtenstein, E. Havivi, R. Shacham, E. Hahamy, R. Leibovich, A. Pevzner, V. Krivitsky, G. Davivi, I. Presman, R. Elnathan, Y. Engel, E. Flaxer and F. Pato
[6] L. Cognet, D. A. Tsyboulski, J. D. R. Rocha, C. D. Doyle, J. M. Tour, R. B. Weisman. Science 316 (2007) 1465-1468.

Research goals

The project is aimed at realizing:
A silicon/Germanium (Si/Ge) sensor for operation in both the visible and the near-infrared. Voltage tunable photodetectors will be obtained by preparing Ge and Si diodes with back to back connection. The polarization of the devices permits to activate one of the two junctions alternatively. The Ge/Si technology has been selected to combine the short wavelength sensitivity (300-900nm) and the superior capability of silicon technology with the NIR sensitivity (800-1800nm) of germanium.
We propose an epitaxial growth procedure of germanium based devices based on the use of isobutyl germane (iBuGe) which is a metal organic precursor having high vapour pressure at room temperature, low background impurity level.
Furthermore we will realise a simplified device able to selectively detect the visible or the near infrared spectra as a demonstrator for a more complex device.

Doped Germanium nanowires for the preparation of ultra-high sensitive explosive detectors using gold as catalyst and doped by fluxing the nanowire dopant precursor in a MOCVD chamber. Attempts to prepare a nanowire based FET transistor will be made by contacting single nanowires between metal contacts that will provide the source and the drain of a FET device.

Carbon nanotubes (CNT) will be grown by the Aerosol CVD technique (ACVD) to obtain single walled and monodispersed nanotubes to be used as explosive detector device after proper functionalization.

Last update: 27/11/2021