The expansive growth of electronics based on inorganic, organic and hybrid materials has lead to the development of a number of significant applications, ranging from low-cost photovoltaics (OPV), electronic paper, and organic light-emitting diodes (OLEDs) to radio-frequency identification (RFID) tags and sensors. Recently, a considerable interest is developing around wearable optical devices. For instance, flexible OLEDs are now being integrated into flexible or textile based displays. Wearable optical sensors can track multiple vital signs such as heart rate, blood pressure and oxygen levels. Other applications for wearables include UV detection, measuring pollutant levels, explosive detection, both indoors and outdoors. Our main focus is on the realization and characterization of several types of sensors and optoelectronic devices on substrates of different nature and their combination with other components to realize smart systems. We address the new fabrication challenges, such as the diverse nature of material properties due to low temperature processing; the study of device performances that depend on the proper detection and measurements of a multitude of electro-optical signals. These research activities are carried out in collaboration with CNR-IMM in Lecce.
Charge injection, trapping and mobility properties
In order to develop highly efficient optoelectronic devices, based on inorganic, organic or hybrid semiconductors, the understanding of the charge transport mechanism, in these classes of materials, is of fundamental importance. However, the small values of charge carrier mobility, which limit the applicability of standard techniques normally used for inorganic semiconductors such as the Hall Effect, have made the study of charge transport mechanism in hybrid and organic materials very challenging. Nowadays, it is clear that only by combining different methods of investigation it is possible to achieve a full understanding of the charge carrier properties.
We apply Time of Flight (TOF), Extraction of equilibrium charge carriers by Linearly Increasing Voltage (CELIV), Space charge limited current (SCLC) techniques to study charge injection, trapping and mobility properties of both high and low conductive materials.
Spatial photo-response of materials and devices
Photocurrent mapping is a valuable tool to directly probe light absorption, as well as transport and collection of the photogenerated charges down to the micrometer scale. The possibility to change the excitation wavelength greatly widens the range of materials which can be analysed, also enabling spectral investigations. So far, the technique has been applied to GaAs Nanowires, GaN Schottky diodes, MEMS structures, GaAs based Varactors, etc.
The Pockels effect is exploited to unveil the internal electric field distribution in radiation detectors based on CdTe and GaAs, without perturbing it. When applied in conjunction with TOF, it provides the remarkable advantage to access both fixed and free charges.
Integrated Optical Sources
Optical microcavities play a key role for the development of novel optoelectronic devices. The aim of this research activity is to realize and characterize organic/hybrid based microcavities.
We study a wide range of materials ranging from inorganic, hybrid, or organic semiconductors to conductive oxides. These latter ones, Transparent Conductive Electrodes (TCEs), which transmit light and conduct electrical current simultaneously, mostly in the visible spectral range, are of increasing importance for information (displays) and energy (photovoltaics, architectural and window glass) technologies. Our main focus is on the realization and characterization of TCEs, using a wide range of depositions techniques from thermal evaporation, e-beam, R.F. Sputtering to solution cast methods.
An extensive morphological, optical and electrical characterization is also performed in order to investigate the degree of roughness, uniformity and transmittance of the films while keeping suitable conductive properties.
Novel NIR Photodetectors based on GaAs Heterostructures exhibiting fast response and high responsivity have been realized and tested. In the proposed devices the presence of 2DEG and/or 2DHG greatly improve the time response down to few ps. Structures based on low-Temperature grown GaAs, Bragg reflectors, and different contacts are investigated. Among the advantages of these devices is the possibility of monolithic incorporation into integrated circuits, creating detector and receiver circuity on a single chip.
- J. Pousset, I. Farella, S. Gambino, A. Cola, “Subgap time of flight: A spectroscopic study of deep levels in semi-insulating CdTe:Cl”, J. Appl. Phys. 119, 105701 (2016), ISSN: 00218979, DOI: 10.1063/1.4943262.
- S. Gambino, A. Genco, G. Accorsi, O. Di Stefano., S. Savasta, S. Patanè, G. Gigli, M. Mazzeo, “Ultrastrong light-matter coupling in electroluminescent organic microcavities”, Applied Materials Today 1, pp. 33–36, (2015), ISSN: 23529407, DOI: 10.1016/j.apmt.2015.08.003.
- S. Gambino, M. Mazzeo, A. Genco, O. Di Stefano, S. Savasta, S. Patanè, D. Ballarini, F. Mangione, G. Lerario, D. Sanvitto, G. Gigli, “Exploring Light–Matter Interaction Phenomena under Ultrastrong Coupling Regime”, ACS Photonics, 1 (10), pp. 1042–1048 (2014), ISSN: 2330-4022, DOI: 10.1021/ph500266d
- S. Gambino, S.-C. Lo, Z. Liu, P. Burn, I.D.W. Samuel, “Charge transport in a highly phosphorescent iridium(III) complex-cored dendrimer with double dendrons”, Adv. Funct. Mater. 22, 157-165, (2012), ISSN: 1616-3028, DOI: 10.1002/adfm.201101727.
Other selected Publications
- S. Gambino, S.G. Stevenson, K.A. Knights, P.L. Burn, I.D.W. Samuel, “Control of charge transport in iridium(III) complex-cored carbazole dendrimers by generation and structural modification”, Adv. Funct. Mater. 19, 317-323, (2009), ISSN: 1616-3028, DOI: 10.1002/adfm.200801144.
MAAT: Molecular NAnotechnology for HeAlth and EnvironmenT (PON R&C 2007-2013 ), (2012-2015).
FT_WOLED: Flexible Transparent White Organic Light Emitting Device, Executive Programme for scientific and technological cooperation between Italy and China – research area “Nanotechnology and Advanced Materials” , (2013-2015).
CE2: Center of Entrepreneurial Engineering (PONa3_00354), (2011-2015)