Effects of temperature and near-substrate plasma density on the structural and electrical properties of dc sputtered germanium thin films

Journal Article · Thu Sep 15 00:00:00 EDT 2011 · Journal of Vacuum Science and Technology. A, International Journal Devoted to Vacuum, Surfaces, and Films

DOI:https://doi.org/10.1116/1.3607410· OSTI ID:22051357

Pollock, Kristin M; Kaufman-Osborn, Tobin; Hiltrop, Jonas; Doyle, James R ^[1]

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1. Department of Physics and Astronomy, Macalester College, St. Paul, Minnesota 55105 (United States)

Germanium thin films were deposited by dc reactive magnetron sputtering as a function of substrate temperature and ion flux using an unbalanced magnetron with an external magnetic field. The ion flux and energy distribution were measured using a retarding field energy analyzer (RFEA), a flat probe with a guard ring, and cylindrical Langmuir probes. The RFEA ion flux, the flat probe saturation currents, and the ion densities inferred from the cylindrical probe data are in very good agreement over a wide range of plasma densities, which were varied both by the external coil current and discharge power. The RFEA ion energy distributions are in good agreement with the plasma potentials inferred from the cylindrical probes, and suggest that the nonuniformity of the plasma in the vicinity of the substrate holder should be considered in the interpretation of probe results in these systems. The deposited films were characterized by x-ray diffraction, Raman spectroscopy, optical transmission, resistivity, and Hall effect measurements. Under low ion bombardment conditions, an abrupt onset of the crystalline phase with respect to temperature is observed in the Raman and x-ray diffraction measurements, and the crystal quality increases with increasing temperature above the transition temperature. The transition is also accompanied by a sharp decrease in film resistivity. The microcrystalline films have a strong preferential orientation in the (220) direction, and are p type with carrier densities in the range 10{sup 18} cm{sup -3} and mobilities in the range 15-30 cm{sup 2}/V-s. The structural and electronic properties of the films are sensitive to the ion flux. Near the transition temperature the effects of increasing ion flux can be attributed to the small temperature rise that accompanies the higher plasma density. At higher temperatures the increased ion flux results in a more random crystallographic orientation, with significantly lower carrier concentrations and only slightly lower carrier mobilities, implying either a reduction in acceptor defect density and/or the creation of compensating n-type defects.

• OSTI ID: 22051357
• Journal Information: Journal of Vacuum Science and Technology. A, International Journal Devoted to Vacuum, Surfaces, and Films, Vol. 29, Issue 5; Other Information: (c) 2011 American Vacuum Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 1553-1813
• Country of Publication: United States
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
36 MATERIALS SCIENCE
CARRIER DENSITY
CARRIER MOBILITY
CRYSTALLOGRAPHY
CYLINDRICAL CONFIGURATION
ELECTRIC CONDUCTIVITY
ENERGY SPECTRA
GERMANIUM
HALL EFFECT
ION BEAMS
ION DENSITY
LANGMUIR PROBE
LIGHT TRANSMISSION
MAGNETIC FIELDS
MAGNETRONS
PLASMA DENSITY
RAMAN SPECTROSCOPY
SPUTTERING
THIN FILMS
TRANSITION TEMPERATURE
X-RAY DIFFRACTION