Conductance fluctuations in undoped hydrogenated amorphous silicon–germanium alloy thin films

Abstract

We report coplanar conductance fluctuations of device quality, undoped hydrogenated amorphous silicon-germanium alloy thin films (a-SiGe:H) measured from 430 to 490 K. The a-SiGe:H alloys produce noise power spectra similar to coplanar undoped a-Si:H films in the same temperature range. The noise power spectrum S n does not fit a single 1=f a power law but rather has two distinct regions, each accurately fitted by a power law, but with different slopes. The low frequency slope a 1 is similar to that observed in undoped a-Si:H films varying from 1.30 to 1.46 for different Ge concentrations and shows a slight temperature dependence. At higher frequencies, the slope a 2 is less than unity and temperature independent but depends on the Ge content of the film. a 2 decreases from 0.60 for no Ge (pure a-Si:H) to 0.15 for 40 at.% Ge. The noise power at lower frequencies increases and at higher frequencies decreases substantially as the temperature increases from 430 to 490 K. We infer that similar noise mechanisms are operating in undoped a-SiGe:H and a-Si:H films but that the Ge content is influencing the noise, particularly the slope at higher frequencies. In addition, the noise has the expected quadratic dependence on bias current and obeys Gaussian statistics.

The effect of aging on the dark conductivity and 1/f noise in hydrogenated microcrystalline silicon thin films

“…The slope and quadratic dependence on dc bias current remained the same for all spectra. The spectra obtained for this sample contrast with those previously measured for amorphous and microcrystalline silicon thin films where a distinct break in the power law produced two frequency ranges with different slope [9][10][11]. The higher frequency region with a lower slope parameter of about 0.60 was interpreted as a second independent noise source in the material.…”

“…Noise spectra from amorphous and microcrystalline materials often show unusual features [9][10][11]. To date, there have been no measurements of noise spectra in air-exposed µc-Si:H. This paper reports the changes in dark conductivity and 1/f noise that occur upon air aging and annealing for a state-of-theart µc-Si:H. Measurements were carried out shortly after deposition and again after aging two year in air in order to study irreversible changes.…”

A theory for Hooge's equation based on temperature fluctuations

“…A range of values from 10 -6 to 10 -1 have been reported for Hooge's parameter for semiconductor films or layers and for the conducting channels of JFET's and HEMT's at low electric fields [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] . Typical values are 10 -4 which is consistent with the doping levels and number of atoms in these materials, Eqn.…”