Determination of the Complex Dielectric Function of Ion-Implanted Amorphous Germanium by Spectroscopic Ellipsometry

Abstract

Accurate reference dielectric functions play an important role in the research and development of optical materials. Libraries of such data are required in many applications in which amorphous semiconductors are gaining increasing interest, such as in integrated optics, optoelectronics or photovoltaics. The preparation of materials of high optical quality in a reproducible way is crucial in device fabrication. In this work, amorphous Ge (a-Ge) was created in single-crystalline Ge by ion implantation. It was shown that high optical density is available when implanting low-mass Al ions using a dual-energy approach. The optical properties were measured by multiple angle of incidence spectroscopic ellipsometry identifying the Cody-Lorentz dispersion model as the most suitable, that was capable of describing the dielectric function by a few parameters in the wavelength range from 210 to 1690 nm. The results of the optical measurements were consistent with the high material quality revealed by complementary Rutherford backscattering spectrometry and cross-sectional electron microscopy measurements, including the agreement of the layer thickness within experimental uncertainty.

In-Situ Control of Defect Dynamics By Ellipsometry During Ion Implantation – Evolution of Disorder and Cavity Structure in Single-Crystalline Ge During Implantation of Sb Ions

“…Broad damage distributions were realized by multiple-step andenergy implantations, which are useful for the determination of optical references. 23 It was also proven that the implantation of heavy elements results in quick total amorphization up to the surface of the sample 38,39 , but without a honeycomb void formation and with less void than found for Ge in the present study.…”

“…for 50-300-keV self-ion bombardment 22 . Structural properties such as the size of crystals or the degree of amorphization can also be determined by optical methods 6,7,9,23 . Rutherford backscattering spectrometry (RBS) allows to reveal the degree of crystallinity, crystal structure (when combined with channeling) and the depth distribution of elements.…”

“…Recently, in an Auger electron spectroscopy study the complementarity of both methods was analyzed 28 . Besides determination of the optical properties 14,15,23,29 , frequently in SiGe alloys 6,11,12 , used in optics or optoelectronics, optical methods are also capable of indirectly determining material properties, such as the crystallinity 19 , disorder 30 or crystal size 7 . Finally, there are numerous electrical characterization methods for the quality control of Ge and Ge NC-based devices.…”

Micro-combinatorial sampling of the optical properties of hydrogenated amorphous $$\hbox {Si}_{1-x}\,\hbox {Ge}_{{x}}$$ for the entire range of compositions towards a database for optoelectronics

“…In Refs. 66 and 67 it was also pointed out that the dielectric function of a-Si and a-Ge substantially depends on the applied deposition method, e.g., chemical vapor deposition, sputtering or amorphization by ion implantation (a smaller optical band gap and a larger broadening in case of the ion implantation-amorphized Si 68 ). The distribution of electron states around the gap energy may largely differ depending on the preparation conditions.…”

“…In terms of the Si and Ge concentration ratio, besides reports dealing with the concentration dependent properties of c-Si 1−x Ge x 25,30,43,69 , there are also numerous studies that focus on amorphous compounds 40,50,[66][67][68][69][70][71][72][73][74] . Comprehensive parameterizations for both the photon energies and compositions were presented for crystalline materials, in many cases supported by density of states calculations 75 , also pointing out the Vegard's lawlike behavior 69 .…”