RE plasma deposition of amorphous silicon-germanium alloys: evidence for a chemisorption-based growth process (original) (raw)
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Plasma deposition of amorphous silicon alloys from fluorinated gases
Pure and Applied Chemistry, 2000
Plasma deposition of a-SiGe, a-Sic and a-SiN alloys starting from fluorinated precursors is overviewed. The growth chemistries are examined on the basis of a unique chemisorption model. Some aspects on the role of F atoms in controlling the gas surface interactions and in determining the material properties are also evidenced.
Amorphous silicon germanium alloy film deposition with in situ plasma diagnostics
Solar Cells, 1988
Amorphous silicon germanium alloy (a-SiGe:H) thin films were deposited by r.f. glow discharge using Sill4, GeH4 and H2 gas mixtures. The Sill 4 and GeHa plasmas were analyzed by in situ coherent anti-Stokes Raman spectroscopy (CARS) to determine the dissociation characteristics of Sill4 and GeHa. In situ CARS measurements of Sill4 and GeH4 number densities were performed during a-SiGe:H film depositions as a function of the r.f. power. The steady-state Sill4 and GeHa depletion are linearly dependent on the r.f. power. The slope of the silane and the germane depletion are measured to be 0.22% (mW cm-2)-i and 0.6% (mW cm-2)-i respectively. The germane depletion is a factor of 2.7 larger than the silane depletion. The silane and germane dissociation rates in a closed-chamber r.f. glow discharge were also measured by CARS. The GeH 4 number density decay time constant depends on the GeH4 partial pressure and the H: dilution. The critical role of the hydrogen dilution in GeH4 containing plasma is to suppress the gas phase polymerization process. The hydrogen dilution effect in the a-SiGe:H film growth is to enhance the germanium content of the film and to reduce the film deposition rate. In situ plasma diagnostics and film characterization measurements were used to develop optimized deposition conditions for producing highly photosensitive a-SiGe:H films. Amorphous SiGe:H films with a light-to<lark conductivity ratio of 8 X 103 and an optical band gap of 1.40 eV were deposited.
Plasma deposition of a–Si, Ge: H, F thin films from SiF4–GeH4–H2 mixtures
Journal of Materials Research, 1989
The deposition of hydrogenated and fluorinated silicon-germanium alloys (Si1−xGex:H.F) by glow discharge decomposition of silicon tetrafluoride (SiF4) and germane (GeH4) mixtures has been studied. Optical emission spectroscopy (OES), for the analysis of the emitting species in plasma phase, and mass spectroscopy (MS) for the analysis of the stable species, are used for the plasma diagnostics. In addition, in situ measurements of the deposition rate by laser interferometry are performed. A series of alloys with germanium content ranging from 0 to 55% has been prepared by varying the gas compositional ratio. Data on the optical gap (Ec), sub-gap absorption, and photo-to-dark conductivity ratio (δσ/σ) are used to evaluate the quality of the materials. An alloy a–Si0.75Ge0.25: H, F having Ec δ 1.5 eV and δσ/σ = 104 has been prepared by adding 1% of GeH4 to SiF4 in the feed.
Amorphous sllicon fi-lrns have been obtained under noduLatlon condltlons from siF4-H2 mlxtures and with slF4 addition to siH4-H2 mlxtures. The effect of these condltlons is to lncrease the film hornogenelty and to control the H content and lts bondtng conflguratlon. Under mo-ilulatlon conditions (Ml{) the H content j-s alwayJ higher than under continuous wave (cw) and the mlcrostructure parameter (R) exhlblts a more complex behavlour in dependence on duty cycle (D. c.) and period (p). The siFi addltion, ar high s1F4/s1Ha rarlo, causes changes ln the plasma. by increaslng the dlscharge-sl4nmetry and 1n the naterlal, by lncreaslng the dark conductlvlty and by inducing structural changes,
Deposition of silicon-germanium alloys under plasma modulation conditions
Journal of Non-Crystalline Solids, 1991
Plasma deposition of a-Si,Ge:H,F films from SiF4-GeH4-H2 mixture, has been investigated by applying a square wave modulation to the r.f. field. The effects of plasma modulation on the thickness and compositional uniformity and on the increase of Ge and H incorporation in the film are reported. A twophases model for the conduction mechanism is preliminarily discussed.
Journal of Materials Research, 2006
We have studied structure and electrical properties of Si 1−Y Ge Y :H films deposited by low-frequency plasma-enhanced chemical vapor deposition over the entire composition range from Y ס 0 to Y ס 1. The deposition rate of the films and their structural and electrical properties were measured for various ratios of the germane/silane feed gases and with and without dilution by Ar and by H 2 . Structure and composition was studied by Auger electron spectroscopy (AES), secondary ion mass spectroscopy (SIMS), and Fourier transform infrared (FTIR) spectroscopy. Surface morphology was characterized by atomic force microscopy (AFM). We found that the deposition rate increased with Y, maximizing at Y ס 1 without dilution. The relative rate of Ge and Si incorporation is affected by dilution. Hydrogen preferentially bonds to silicon. Hydrogen content decreases for increasing Y. In addition, optical measurements showed that as Y goes for 0 to 1, the Fermi level moves from mid gap to the conduction band edge; i.e., the films become more n-type. No correlation was found between the pre-exponential and the activation energy of conductivity. The behavior of the conductivity ␥-factor suggests a local minimum in the density of states at E ≈ 0.33 eV for the films grown with or without H-dilution and E ≈ 0.25 eV for the films with Ar dilution.
Plasma deposition of amorphous silicon films: an overview on some open questions
Pure and Applied Chemistry, 2000
Results on amorphous silicon deposition by SiH SiF and Sic1 glow discharges are discussed so as to better understand the plasma phase processes leading to the growth precursors, the plasma/surface interaction and the microscopic parameters affecting the material properties. In particular, the chemical activity of both silicon radicals, hydrogen and halogen atoms, as well as charged particles in the gas phase and on the surface is examined.
Techniques for measuring the composition of hydrogenated amorphous silicon–germanium alloys
Journal of Non-Crystalline Solids, 2000
We grow hydrogenated amorphous silicon-germanium alloys by the hot-wire chemical vapor deposition technique at deposition rates between 0.5 and 1.4 nanometers per second. We prepared a set of these alloys to determine the concentrations of the alloying elements as measured by various techniques. This set consists of samples throughout the range of germanium alloying from 0% (a-Si:H) to 100% (a-Ge:H). We find that by making the appropriate calibrations and corrections, our compositional measurements agreement between the various techniques. Nuclear reaction analysis, Fourier transform infrared spectroscopy, and secondary ion mass spectrometry (SIMS) all yield similar hydrogen contents, within ± 20% for each sample. Electron probe micro-analysis (EPMA) and SIMS yield silicon and germanium contents within ± 7% of each other with results being confirmed by Rutherford backscattering. EPMA oxygen measurements are affected by highly oxidized surface layers, thus these data show larger O concentrations than those measured by SIMS.