Morphology and texture evolution of nanostructured CaF₂films on amorphous substrates under oblique incidence flux

Abstract

The morphology and biaxial texture of vacuum evaporated CaF(2) films on amorphous substrates as a function of vapour incident angle, substrate temperature and film thickness were investigated by scanning electron microscopy, x-ray pole figure and reflection high energy electron diffraction surface pole figure analyses. Results show that an anomalous [220] out-of-plane texture was preferred in CaF(2) films deposited on Si substrates at < 200 °C with normal vapour incidence. With an increase of the vapour incident angle, the out-of-plane orientation changed from [220] to [111] at a substrate temperature of 100 °C. In films deposited with normal vapour incidence, the out-of-plane orientation changed from [220] at 100 °C to [111] at 400 °C. In films deposited with an oblique vapour incidence at 100 °C, the texture changed from random at small thickness (5 nm) to biaxial at larger thickness (20 nm or more). Using first principles density functional theory calculation, it was shown that [220] texture formation is a consequence of energetically favourable adsorption of CaF(2) molecules onto the CaF(2)(110) facet.

Limits on Passivating Defects in Semiconductors: The Case of Si Edge Dislocations

“…µ s is a resultant of our imposed constraint on the system, and is an effective Fermi energy that acts as a demarcation line to separate effective and ineffective doping. As an explicit example of our theory, our case study deals with an edge dislocation (ED) in Si since Si and Ge with small-angle grain boundaries, consisting of a series of EDs, are candidates for low cost/high quality PV materials [8]. Using substitutional dopants as our passivation candidates, we calculate their ∆E using first-principles density functional theory(DFT), and depict the resultant connection between the dopants and their passivation efficiencies through the universal curve in in Fig.…”

RHEED Pole Figure Measurements of Biaxial Thin Film Growth Front Evolution

“…Thus far we have used the RHEED surface pole figure technique to characterize a number of nanostructured films including Ru [23], Mg [24], W [34], and CaF 2 [35,36]. All these films were deposited using the oblique angle deposition (or inclined-substrate deposition) technique [37][38][39][40][41][42][43].…”

“…We have performed in situ and ex situ RHEED surface pole figure measurements and analyses of metals and insulators on amorphous substrates [22,34,35]. Here we will give an example of an ex situ study of the texture evolution of CaF 2 .…”

“…Here we will give an example of an ex situ study of the texture evolution of CaF 2 . Our previous work shows that CaF 2 nanorods grown by the oblique angle vapor deposition on amorphous substrates exhibit a biaxial texture [35,36]. This CaF 2 can be used as a buffer layer to grow biaxial thin films for various applications [6,7,9,10].…”

The role of faceting in biaxially textured thin films: Columnar morphology and abnormal tilting

“…Despite the success in the above-mentioned models, there remain a number of biaxially textured thin films that produce β angles deviating substantially from any of the existing model predictions. Nanostructured MgO thin films 1,12,16,17 , CaF 2 nanorods 10,18 , Mg nanoblades 11,19 , AlN columns 20 and Mo-Al nanofins 21 are examples of systems exhibiting abnormal tilt angles. The columns developed in these thin films are wellaligned single crystals tilted at angles that deviate significantly from existing predictions.…”