Nanoscale Study of the Hydrogenated Amorphous Silicon Surface

1994 ◽  
Vol 336 ◽  
Author(s):  
D.M. Tanenbaum ◽  
A. Laracuente ◽  
A.C. Gallagher
Keyword(s):  
Surface Roughness ◽  
Amorphous Silicon ◽  
Hydrogenated Amorphous Silicon ◽  
Rf Discharge ◽  
Scanning Tunneling ◽  
Growth Stages ◽  
Crystal Silicon ◽  
Air Exposure ◽  
Atomically Flat ◽  
Hydrogenated Amorphous

ABSTRACTA scanning tunneling microscope has been used to study the topology of the surface of device-quality, hydrogenated Amorphous silicon deposited by rf discharge from silane or “hot wire” CVD. The substrates were oxide-free single-crystal silicon or GaAs. Films studied were either grown in our laboratory and observed with no air exposure, or grown at other laboratories producing device-quality photovoltaic cells and viewed after air exposures of less than 30 Minutes. Thin films (10 nm) representing early growth stages appear significantly smoother than the thicker films. The topology of thick films (> 50 nm) has large variations over individual samples. While many regions can be characterized as “rolling hills”, atomically flat areas are sometimes observed nearby in our films. In most regions the observed slopes were 10% or less from the horizontal, but some steep-sided valleys, indicating incipient voids, are seen. Overall surface roughness measured on sub-Micron areas of our films is very inhomogeneous. Uniformity of the films grown off site was much better, although no atomically flat regions were observed, surface roughness can be estimated.

Growth and Nucleation of Hydrogenated Amorphous Silicon on Silicon (100) Surfaces

1995 ◽  
Vol 377 ◽  
Author(s):  
D. M. Tanenbaum ◽  
A. Laracuente ◽  
A. C. Gallagher
Keyword(s):  
Film Thickness ◽  
Amorphous Silicon ◽  
Correlation Length ◽  
Hydrogenated Amorphous Silicon ◽  
Film Surface ◽  
Scanning Tunneling ◽  
Dynamic Scaling ◽  
Initial Growth ◽  
Air Exposure ◽  
Hydrogenated Amorphous

ABSTRACTA scanning tunneling microscope (STM) has been used to study the topology of the surfaces of a series of thin hydrogenated amorphous silicon (a-Si:H) films deposited by rf discharge from pure silane. The substrates were atomically flat, oxide-free, single-crystal Si (100). Films were grown in our laboratory and transferred to the STM with no air exposure between growth and measurement. A series of thin films between 1 and 50 nm in thickness reveals the initial growth stage of a-Si:H on Si (100). Initial nucleation and islanding can be seen on these films. The surface has a distribution of island sizes. The rms roughness and a surface lateral correlation length were measured as functions of film thickness. The rms roughness grows sublinearly with thickness from 0.3–0.5 nm as the film thickness is raised from 1 to 50 nm. The lateral size of the surface features also grows with film thickness. The growth of the roughness and correlation length can be compared with the dynamic scaling model. In addition, the topographs reveal occasional structures of larger size and low density on the film surface. These structures are nanoparticles of silicon deposited from the plasma during film growth. The frequency of these features scales with film thickness, and represents 10−510−4 of the total film volume.

Photo-Oxidation of Hydrogenated Amorphous Silicon-Carbon Alloys

1989 ◽  
Vol 158 ◽  
Author(s):  
P. John ◽  
I.M. Odeh ◽  
A. Qayyum ◽  
J.I.B. Wilson
Keyword(s):  
Amorphous Silicon ◽  
Photoelectron Spectroscopy ◽  
Crystalline Silicon ◽  
Hydrogenated Amorphous Silicon ◽  
Rf Discharge ◽  
Silicon Substrates ◽  
Capacitively Coupled ◽  
X Ray ◽  
Silicon Carbon ◽  
Hydrogenated Amorphous

ABSTRACTHydrogenated amorphous silicon-carbon alloys, a-Si:C:H, have been deposited as thin films (d=0.1-0.5 micron) on crystalline silicon substrates from a capacitively coupled rf discharge in silane-propane mixtures. Variations in the stoichiometry of the films were achieved by altering the ratio of SiH4 to C3H8 flow rates at a sbstrate temperature in the range 240-260°C and total pressure between 30-70 mtorr. The silicon to carbon ratios were established by X-ray photoelectron spectroscopy, XPS, and the hydrogen content and distribution by infra-red spectroscopy.

Hydrogenated amorphous silicon studied by scanning tunneling microscopy

1988 ◽  
Vol 63 (9) ◽  
pp. 4515-4517 ◽  
Author(s):  
R. Wiesendanger ◽  
L. Rosenthaler ◽  
H. R. Hidber ◽  
H.‐J. Güntherodt ◽  
A. W. McKinnon ◽  
...  
Keyword(s):  
Scanning Tunneling Microscopy ◽  
Amorphous Silicon ◽  
Hydrogenated Amorphous Silicon ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Hydrogenated Amorphous

Higher Crystalline Volume Yields from Excimer Laser Crystallization of Amorphous Silicon with an Asymmetrical Peak Pulse Profile

2007 ◽  
Vol 31 ◽  
pp. 185-188 ◽  
Author(s):  
A.A.D.T. Adikaari ◽  
N.K. Mudugamuwa ◽  
S.R.P. Silva
Keyword(s):  
Surface Roughness ◽  
Amorphous Silicon ◽  
Laser Energy ◽  
Hydrogenated Amorphous Silicon ◽  
Leading Edge ◽  
Gaussian Pulse ◽  
Large Area ◽  
Pulse Profile ◽  
Beam Shape ◽  
Hydrogenated Amorphous

Excimer lasers have been utilized for the crystallization of hydrogenated amorphous silicon for electronic applications. These lasers typically operate in the ultraviolet and hence photons are absorbed by the silicon thin films within a few nanometres of the surface, melting and solidifying the silicon on a nanosecond timescale, often without affecting the underlying substrate. This technique enables the use of inexpensive substrates, such as glass, which are highly preferable for low cost, large-area electronic devices. The depth of crystallization becomes important for applications such as photovoltaics, which depends on a number of factors; with laser beam shape one of the most significant. A Gaussian beam profile has been reported to be best suited for controlled evolution of hydrogen during crystallization with minimum surface damage. Previous reports show the typical energy densities of crystallization, comparing the crystalline volume and surface roughness of the resultant films for different film thicknesses. We report significant reductions of laser energy densities for crystallization by modifying the Gaussian pulse profile, while retaining the controlled evolution of hydrogen from hydrogenated amorphous silicon films. An asymmetrical, shorter pulse profile retains the desirable gradual leading edge of the Gaussian pulse for controlled evaporation of hydrogen, while increasing the peak energy. The resultant films show increased surface roughness along with higher crystalline volumes, which may be beneficial for photovoltaics.

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