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Title: Strength, stiffness, and microstructure of Cu(In,Ga)Se{sub 2} thin films deposited via sputtering and co-evaporation

This work examines Cu(In,Ga)Se{sub 2} thin films fabricated by (1) selenization of pre-sputtered Cu-In-Ga and (2) co-evaporation of each constituent. The efficiency disparity between films deposited via these two methods is linked to differences in morphology and microstructure. Atomic force microscopy and scanning electron microscopy show that selenized films have rougher surfaces and poor adhesion to molybdenum back contact. Transmission electron microscopy and electron energy loss spectroscopy revealed multiple voids near the Mo layer in selenized films and a depletion of Na and Se around the voids. Residual stresses in co-evaporated films were found to be ∼1.23 GPa using wafer curvature measurements. Uniaxial compression experiments on 500 nm-diameter nanopillars carved out from co-evaporated films revealed the elastic modulus of 70.4 ± 6.5 GPa. Hertzian contact model applied to nanoindentation data on selenized films revealed the indentation modulus of 68.9 ± 12.4 GPa, which is in agreement with previous reports. This equivalence of the elastic moduli suggests that microstructural differences manifest themselves after the yield point. Typical plastic behavior with two distinct failure modes is observed in the extracted stress-strain results, with the yield strength of 640.9 ± 13.7 MPa for pillars that failed by shearing and 1100.8 ± 77.8 MPa for pillars that failed by shattering.
Authors:
; ;  [1] ;  [2] ;  [3] ; ; ;  [4]
  1. Division of Applied Science and Engineering, California Institute of Technology, 1200 E California Blvd., Pasadena, California 91125 (United States)
  2. Graduate Institute of Photonics and Optoelectronics and Department of Electrical Engineering, National Taiwan University, No. 1, Sec 4 Roosevelt, Taipei 10617, Taiwan (China)
  3. Department of Electrical Engineering, National Taiwan University, No 1, Sec 4 Roosevelt, Taipei 10617, Taiwan (China)
  4. National Nano Device Laboratories, Hsinchu Science Park, No. 26, Prosperity Road I, Hsinchu 30078, Taiwan (China)
Publication Date:
OSTI Identifier:
22303942
Resource Type:
Journal Article
Resource Relation:
Journal Name: Applied Physics Letters; Journal Volume: 105; Journal Issue: 1; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; ATOMIC FORCE MICROSCOPY; COPPER SELENIDES; ENERGY-LOSS SPECTROSCOPY; EVAPORATION; FLEXIBILITY; GALLIUM COMPOUNDS; INDIUM COMPOUNDS; LAYERS; MICROSTRUCTURE; PRESSURE RANGE GIGA PA; RESIDUAL STRESSES; SCANNING ELECTRON MICROSCOPY; SPUTTERING; STRAINS; SURFACES; THIN FILMS; TRANSMISSION ELECTRON MICROSCOPY; YIELD STRENGTH