Semiconductors containing nanopores have gained a renewed interest as they are able to adsorb and interact with atoms and molecules and can thus be used in several interesting and emerging applications. Ge film and bulk samples, self-implanted with Ge+ ions, have shown to have a sponge-like nanoporous structure [1], as shown in fig.1. Possible applications of porous semiconductors include various novel sensors, solar cells, optoelectronic devices; they can be used for catalysis, biological molecular isolation and purification or electrodes for micro-fuel cells [2 and reference therein]. Optoelectronic characterization of the layers are carried out by Surface Photovoltage (SPV) Spectroscopy, a powerful technique which allows for obtaining detailed information on material optical properties, such as electronic transitions at gap states, and band to band transitions [2,3]. In addition, structural and microscopic analyses have been carried out in order to identify amorphous or crystalline phases and the average size of the nano- pores. Different nanoporous (np) structures have been investigated: crystalline and amorphous np-Ge obtained by implantation of bulk Ge, as well as crystalline and amorphous np-Ge obtained by ion implantation of Ge film grown on Si substrates by molecular beam epitaxy and sputtering. The effect of Au nanoparticles embedded within the nanoporous structure has been also investigated. Changes in the SPV spectra as a function of ion implantation fluence and annealing treatments have been found and discussed on the basis of the structural properties of the samples [4]. A significant enhancement of the SPV signal in np-Ge samples decorated with Au nanoparticles has been shown, and related to enhanced light trapping effects. SPV spectra of np-Ge thin films show the main peak, which corresponds to band-to-band transitions, significantly blue shifted with respect to the same peak in bulk np-Ge (fig.2). This result has been assigned to a quantum confinement effect occurring at Ge nano- walls separating the nanopores. In addition, a strong enhancement of the SPV signal has been observed due to light confinement effects. Quantum confinement and light trapping effects demonstrated in nanoporous Ge film deposited on Si substrate can be of major interest for future photovoltaic applications of thin film solar cells. [1] G Impellizzeri et al Nanotechnology 23, 395604 (2012) [2] D Cavalcoli et al Microporous and Mesoporous Mat 196, 175–178 (2014) [3] L Kronik and Y. Shapira, Surf Sci Rep. 37,1 (1999) [4] D Cavalcoli et al, in Semiconductors and Semimetals, Elsevier, (2015)
Quantum confinement and light trapping effects in nanoporous Ge
CAVALCOLI, DANIELA;FRABONI, BEATRICE;
2015
Abstract
Semiconductors containing nanopores have gained a renewed interest as they are able to adsorb and interact with atoms and molecules and can thus be used in several interesting and emerging applications. Ge film and bulk samples, self-implanted with Ge+ ions, have shown to have a sponge-like nanoporous structure [1], as shown in fig.1. Possible applications of porous semiconductors include various novel sensors, solar cells, optoelectronic devices; they can be used for catalysis, biological molecular isolation and purification or electrodes for micro-fuel cells [2 and reference therein]. Optoelectronic characterization of the layers are carried out by Surface Photovoltage (SPV) Spectroscopy, a powerful technique which allows for obtaining detailed information on material optical properties, such as electronic transitions at gap states, and band to band transitions [2,3]. In addition, structural and microscopic analyses have been carried out in order to identify amorphous or crystalline phases and the average size of the nano- pores. Different nanoporous (np) structures have been investigated: crystalline and amorphous np-Ge obtained by implantation of bulk Ge, as well as crystalline and amorphous np-Ge obtained by ion implantation of Ge film grown on Si substrates by molecular beam epitaxy and sputtering. The effect of Au nanoparticles embedded within the nanoporous structure has been also investigated. Changes in the SPV spectra as a function of ion implantation fluence and annealing treatments have been found and discussed on the basis of the structural properties of the samples [4]. A significant enhancement of the SPV signal in np-Ge samples decorated with Au nanoparticles has been shown, and related to enhanced light trapping effects. SPV spectra of np-Ge thin films show the main peak, which corresponds to band-to-band transitions, significantly blue shifted with respect to the same peak in bulk np-Ge (fig.2). This result has been assigned to a quantum confinement effect occurring at Ge nano- walls separating the nanopores. In addition, a strong enhancement of the SPV signal has been observed due to light confinement effects. Quantum confinement and light trapping effects demonstrated in nanoporous Ge film deposited on Si substrate can be of major interest for future photovoltaic applications of thin film solar cells. [1] G Impellizzeri et al Nanotechnology 23, 395604 (2012) [2] D Cavalcoli et al Microporous and Mesoporous Mat 196, 175–178 (2014) [3] L Kronik and Y. Shapira, Surf Sci Rep. 37,1 (1999) [4] D Cavalcoli et al, in Semiconductors and Semimetals, Elsevier, (2015)I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
