Optical and electrical properties of very thin chromium films for optoelectronic devices

Abstract

Abstract. Establishing the optimal experimental conditions for the development of transparent metal contacts to be used in optoelectronic devices, such as organic light-emitting diodes and solar cells, is an important task. In this paper we present an overview of the development of very thin e-beam-deposited chromium films with high optical transparency. The surface morphology is investigated by scanning electron microscopy. The variation is examined of the films' electrical and optical properties (transmittance and complex refractive index) with the variation of the thickness and deposition rate. We observed that, for a given thickness of the chromium films, the absorption coefficient increases when the deposition rate is decreased. We also found that the thin films with a thickness of less than 10 nm show an average transmittance exceeding 60 % in the spectral range 400 -1500 nm. The films' resistivity, ρ, is determined by the four-point probe method. The value of ρ varies in the range of 10 -3 − 10 −4 Ω cm for chromium coatings in the thickness interval 5 − 100 nm. The results obtained show that very thin metal films could be an alternative to the transparent conductive oxides. IntroductionThin chromium films have found many applications, for example as layers for improvement of the adhesion to transparent substrates [1], in mask production [2] and as transparent electrodes [3]. Recently, it has been demonstrated that the ultrathin transparent metal contacts provide a number of advantages over the more commonly used conductive transparent metal oxides, such as indium tin oxide (ITO) [4]. According to [5], chromium and nickel thin films possess optical transparency comparable to that of the ITO in the visible and near-infrared range (0.4 − 2.5 μm), while it can be significantly higher in the ultraviolet (175 − 400 nm) and mid-infrared (2.5 − 25 μm) regions.The conditions of deposition, as deposition rate, temperature of substrate, etc., influence very strongly the properties of the metal coating [6]. It has been shown that the deposition rate and argon partial pressure in the case of cathode sputtering strongly affect the microstructure and electrical properties of thin chromium films [7,8]. Metal films deposited by ion-beam sputtering display exceptionally low surface roughness, the films being as thin as about 20 Å [3].The goal of the present work is the investigation of the optical and electrical properties of very thin chromium films deposited by an electron-beam technique.

Femtosecond control of phonon dynamics near a magnetic order critical point

“…Values for heat capacities obtained from fitting are within the expected range: the ratio between the lattice and electronic heat capacities during the excitation ( ~ 7) is comparable to that extracted from previous experiments 29 (larger values than in bulk 35 can be explained by disorder in the film 39 ), as is the value of thermal coupling constant k 35 . Absorption at 800 nm wavelength and 30° angle can be estimated based on measured complex refraction index for Cr thin films 40 as ~20%, while the obtained value of gives absorption of , which is remarkably close considering possible differences due to film roughness. With these fitted parameters, our theoretical model provides an excellent quantitative agreement with the experiment, as Fig.…”

Influence of RF power on the stoichiometry, optical, and electrical properties of chromium oxide coatings prepared by reactive magnetron sputtering

“…This is consistent with our electrical resistivity measurement reported here. An increase in the RF Lozanova et al [38] have previously examined the optical and electrical properties of chromium thin films of thickness values 5nm -100 nm prepared by electron beam technique.…”

“…The low resistivity value and high optical transmittance exhibited by the thin films prepared at lower deposition powers (e.g. sample prepared at 300W/10sccm) makes the film a promising transparent conducting oxide (TCO) for optoelectronic devices and other similar applications [38,41].…”

Phase Uncertainty in Digital Holographic Microscopy Measurements in the Presence of Solution Flow Conditions

“…The Fresnel reflection coefficient, rpq, at the interface of two media, p and q, for perpendicularly incident light is a function of the refractive indices of the two media, np and nq: At wavelength λ1, the refractive indices of chromium and glass are around 3.5 [41] and 1.5, respectively, so R is approximately 78 %, which suggests that even if the chromium is transparent, the reflectivity is relatively high. For very thin layers, it has been shown that chromium does demonstrate transparency (e.g., about 50 % transmittance with a wavelength around λ1 for an 18 nm chromium layer [42]), but thicker coatings of chromium have demonstrated zero transmittance. For instance, Rauf et al [43] found zero transmittance in the wavelength range of 300 nm to 700 nm for a chromium layer thickness of 200 nm, and Wang et al [44] found zero transmittance at a wavelength of 550 nm for chromium layer thicknesses ≥ 100 nm.…”