Nano-structured Ge_ySi_1-y:H Films Deposited by Low Frequency Plasma for Photovoltaic Application

Abstract

In this work we present the study of fabrication, Ge incorporation, structure and electronic properties of nano-structured Ge y Si 1-y :H films with y>0.5 prepared by low frequency (LF) PECVD. Ge y Si 1-y :H films were deposited by LF PECVD at a frequency f= 110 kHz from SiH 4 +GeH 4 +H 2 gas mixture. SiH 4 and GeH 4 flows were varied to fabricate the films in wide range of 0<y<l. Hydrogen dilution was varied in the range of R H =20 to 80. Structure of the films was studied by AFM and SEM with consequent image processing to extract statistical parameters such as grain distribution and mean values. Composition of the films was characterized by SIMS and EDX. Electronic properties were characterized by temperature dependence of conductivity, spectral dependence of optical absorption. Sub-gap absorption was characterized by Urbach energy, E U; and defect absorption, α D . We observed grain like nano-structure with Gauss distribution of grain diameters by both AFM and SEM measurements. The most interesting films had mean grain diameter<D> = 24.0±0.7 nm, dispersion ∆D=11.0±0.2 nm and fill factor FF=0.313, Ge content y=0. . These films showed also the lowest values of Urbach energy E U =0.030 eV and low defect absorption α D = 5xl0 2 cm -1 (at photon energy hν = 1.04 eV) indicating on low density of localized states in mobility gap. Doped films have been also fabricated and studied. Finally we shall discuss application of the above films in photovoltaic devices.

Hybrid Silicon-Organic Heterojunction Structures for Photovoltaic Applications

“…Good electronic properties for interesting high Ge-content nanostructured Si x Ge y :H films deposited at 300°C, high H-dilution ratio, and low frequency have been systematically reported in Ref. [10]. On the other hand, one of the main characteristics of the PECVD technique to take advantage for actual applications is the relative low temperature process in the range of 100-300°C.…”

Sub-gap Photoconductivity in Germanium-silicon Films Deposited by Low Frequency Plasma

“…It has been also demonstrated that Ge x Si 1-x :H films with x>0.95 have shown superior electronic properties in comparison with those in Ge:H films having practically the same optical gap [4][5][6].…”

“…Some devices with Ge:H films have been reported [1,2], where Ge:H was used as the intrinsic layer in p-i-n structures, however, doped nand p-layers were fabricated of silicon. In our previous studies [4,5] we have demonstrated a LF PECVD fabrication of Ge:H and Ge x Si 1-x :H films with both low tail and deep localized states. In this respect low frequency (LF) PECVD with its inherent higher ion bombardment than that in conventional RF plasma is very attractive.…”

Electrical characterization of a‐C:H as a dielectric material in metal/insulator/metal structures

“…PECVD carbon-based materials are proposed here because we have developed a well controlled deposition technique to obtain films with excellent electrical properties such as a very low-K (2.1), a high resistivity (10 14 Ω-cm), and a high breakdown electric field (~10 6 V/cm) [4]. In order to obtain an effective use of a-C:H films for the fabrication of integrated circuits (IC's), a better understanding of the current transport mechanisms governing their electrical behaviour is required.…”

“…The hydrogen content of the dilution in the gas phase was set to 25%, the pressure at 1.6 Torr, and the substrate temperature was 350 ºC. Further details of the deposition process and the structure stability of the a-C:H films have been reported in [4,7]. The fabrication procedure of the MIM structure was conducted as follows.…”