High performance glow discharge a-Si{sub 1{minus}x}Ge{sub x}:H of large x
- Division of Applied Sciences, Harvard University, Cambridge, Massachusetts 02138 (United States)
- Department of Physics, Boston College, Chestnut Hill, Boston, Massachusetts 02167 (United States)
- Department of Physics, University of Oregon, Eugene, Oregon 97403 (United States)
- Department of Physics, Colorado School of Mines, Golden, Colorado 80401 (United States)
Radio frequency glow discharge chemical vapor deposition has been used to deposit thin films of a-Si{sub 1{minus}x}Ge{sub x}:H which possess optoelectronic properties that are greatly improved over any yet reported in the range of x{ge}0.6. These films were deposited on the cathode (cathodic deposition) of an rf discharge. Their properties are assessed using a large variety of measurements and by comparison to the properties of alloys conventionally prepared on the anode (anodic deposition). Steady state photoconductivity measurements yield a quantum-efficiency-mobility-lifetime product, {eta}{mu}{tau}, of (1{endash}3){times}10{sup {minus}7}cm{sup 2}V{sup {minus}1} for 1.00{ge}x{ge}0.75 and (6{endash}10){times}10{sup {minus}8}cm{sup 2}V{sup {minus}1} for 0.75{ge}x{ge}0.50, and photocarrier grating measurements yield ambipolar diffusion lengths several times greater than previously obtained for alloys of large x. It is confirmed that the improvements in phototransport are not due to a shift in the Fermi level. In fact, results of recent measurements on lightly doped samples strongly suggest that for these cathodic alloys neither photocarrier is dominant [({mu}{tau}){sub e}{approx}({mu}{tau}){sub h}]. The improvements are attributed in large part to the reduction of long range structural heterogeneity observed in x-ray scattering and electron microscopy, and partly to the reduction in midgap state density. In spite of the superior properties, an assessment of the data of the cathodic alloys suggests that alloying introduces mechanisms detrimental to transport which are not present in a-Si:H or a-Ge:H. The Urbach tail width is 42{plus_minus}2 meV for cathodic a-Ge:H and 45{plus_minus}2 meV for cathodic a-Si{sub 1{minus}x}Ge{sub x}:H and is constant with x. From differences in the band edges and tails we infer that the atomic bond ordering is different between the cathodic and anodic alloys. (Abstract Truncated)
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 496655
- Journal Information:
- Journal of Applied Physics, Vol. 81, Issue 9; Other Information: PBD: May 1997
- Country of Publication:
- United States
- Language:
- English
Similar Records
Structural and electronic studies of a-SiGe:H alloys. Final subcontract report, 1 January 1991--28 February 1993
Structural and Electronic Studies of a-SiGe:H Alloys, Final Subcontract Report, 1 January 1991 - 28 February 1993