Electrical and optical properties of amorphous vs crystalline GeTe films

Bahl, S. K. ; Chopra, K. L. (1969) Electrical and optical properties of amorphous vs crystalline GeTe films Journal of Vacuum Science and Technology, 6 (4). pp. 561-565. ISSN 0022-5355

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Official URL: http://avspublications.org/jvst/resource/1/jvstal/...

Related URL: http://dx.doi.org/10.1116/1.1315683


Ac and dc conductivity, tunneling, and optical transmission and reflectance studies have been made on amorphous and crystalline (rhombohedral and NaCl) GeTe films (80 Å to 10 μ thick) prepared by evaporation and by sputtering. The crystalline films behave like a p-type degenerate semiconductor with Fermi level ˜0.3-0.5 eV in the valence band, resistivity ˜10-4 Ωcm, carrier concentration ˜1020 to 1021/cm3, Hall mobility ˜25-120 cm2/V sec, and a small, positive (metallic) temperature coefficient of resistivity. Amorphous films show a high resistivity which increases exponentially from ˜103 to >1010 Ω cm as the temperature decreases from 300-77 K, corresponding to an activation energy of 0.3-0.4 eV. The ac conductivity increases as ωn(n<1) to approach a constant value above ω = 90 kc. Simultaneously, the activation energy for conduction decreases continuously to a nearly zero value. The conductivity also increases rapidly as a high power of the electric field at >104 V/cm. The near infrared indices of amorphous and crystalline structures are 4.0 and 5.6, respectively. The optical absorption edge is nearly the same (˜0.8 eV) for the crystalline and amorphous films. A tentative explanation of the transport behavior of amorphous films is possible in terms of conduction by two parallel mechanisms: (a) in the conduction band by intrinsically excited carriers, and (b) by a hopping process in the trap-like localized levels above the Fermi level in the valence band.

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Deposited On:22 Dec 2011 14:08
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