Experimental Studies of Long-Range Atomic H Motion and Desorption in Hydrogenated Amorphous Silicon and Germanium [Thesis]

Thesis/Dissertation · Thu Jul 11 04:00:00 EDT 1991

OSTI ID:5643940

Wu, Xiao-Lin ^[1]

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1. Iowa State Univ., Ames, IA (United States); Ames Laboratory (AMES), Ames, IA (United States)

Long-range H motion and desorption in low hydrogen concentration undoped hydrogenated amorphous silicon (a-Si:H) and germanium (a-Ge:H) was studied by deuterium secondary ion mass spectrometry (SIMS) depth profiles and IR absorption of a-Si:H/a-Si:(H,D)/a-Si:H and a-Ge:H/a-Ge:(H,D)/a-Ge:H. SIMS monitors deuterium motion (assumed similar to that of H), while IR yields information on hydrogen content and bonding. The diffusion constant was found to be dispersive with time, and depended on H content C_H, diffusion length L, and microvoid content, at temperatures T ≤ 400 °C for a-Si:H and T ≤ 310 °C for a-Ge:H. It exhibited a power-law D(t) = D_oo(ωt)^–α relation in both systems. In a-Si:H, α generally deviates from the 1 – T/T_o dependence on the temperature T expected from a multiple trapping mechanism. The diffusion constant at constant diffusion length D(t_L) then deviates from an Arrhenius dependence on the temperature. The "apparent" activation energy E_a and prefactor D_o, defined by the linear best-fit of lnD(t_L) vs 1/T, strongly increase with L at low C_H. The Meyer-Neldel relation (MNR) D_o = A_ooexp(E_a/T_o') , where A_oo ≃ 3.1x10^–14 cm²/s and T_o' ≃ 730 K, holds for all 1.3 ≤ E_a ≤ 2.4 eV and 2.5x10^–5 ≤ D_o ≤ 3100 cm²/s. In a-Ge:H, α is essentially temperature and composition independent, but increases with microvoid content. The activation energy E_a ranges from 0.7 to 1.2 eV among the various films. The Meyer-Neldel relation is observed, with A_oo ≃ 5.5x10^–16 cm²/s and T_o' ≃ 530 K. These values are lower than the corresponging values in a-Si:H. Hydrogen desorption temperature is as low as 180 °C. Yet the significance of the MNR is questionable in both a-Si:H and a-Ge:H. The diffusion results for both a-Si:H and a-Ge:H are discussed in relation to the microstructure of the films. The nature of the microvoid-induced deep H-trapping sites is also discussed. Finally, a possible relation between the dispersive diffusion and a percolation model is presented.

• Research Organization: Iowa State Univ., Ames, IA (United States); Ames Laboratory (AMES), Ames, IA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES)
• DOE Contract Number: W-7405-ENG-82
• OSTI ID: 5643940
• Report Number(s): IS-T--1559; ON: DE91016161
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360104* -- Metals & Alloys-- Physical Properties
CHEMICAL BONDS
CRYSTAL STRUCTURE
DESORPTION
DIFFUSION
DIMENSIONS
ELECTRON SPIN RESONANCE
ELECTRONIC STRUCTURE
ELEMENTS
GERMANIUM
HYDROGEN
MAGNETIC RESONANCE
MASS SPECTROSCOPY
MATERIALS
METALS
MICROSTRUCTURE
NONMETALS
RESONANCE
SAMPLE PREPARATION
SEMICONDUCTOR MATERIALS
SEMIMETALS
SILICON
SORPTIVE PROPERTIES
SPECTROSCOPY
SPUTTERING
SURFACE PROPERTIES
THICKNESS