Comparison of VHF, RF and Dc Plasma Excitation for a-Si:H Deposition with Hydrogen Dilution

Abstract

A comparative study of DC, RF and VHF excitation for the plasma enhanced chemical vapor deposition (PECVD) of intrinsic layers of a-Si:H is presented, with special emphasis on the effects of hydrogen dilution. Growth rates at comparable plasma power, for substrate temperatures between 100°C and 300°C and for various H 2 dilution ratios are presented, along with optical bandgap, H content, and electronic transport properties in the light-soaked state.H 2 strongly reduces the growth rate for all techniques. The growth rate for the highest H 2 dilution ratio is approximately four times higher for VHF than for DC or RF excitation. In all three cases increasing the substrate temperature reduces the optical gap and the H content C H . Raising the substrate temperature slightly enhances the stability of undiluted films. H 2 dilution increases the optical gap for all three techniques. The H content of RF-and VHF-deposited samples increases with increasing H 2 dilution ratio, while in DC deposition it produces an initial drop of the H content, followed by an increase. In all three cases, H 2 dilution improves the electronic transport properties of the material by roughly a factor of two. The gain in stability is most pronounced for relatively small dilution; in the case of DC deposition, too strong a dilution even has an adverse effect on stability.

Amorphous silicon solar cells with stable protocrystalline silicon and unstable microcrystalline silicon at the onset of a microcrystalline regime as i-layers

“…We should point out that the increase of C H in films with increasing R is not unique. Not all hydrogen dilution techniques increase hydrogen content; it has been reported that hydrogen dilution can decrease C H [13]. Our results also show that the amount of degradation has no dependence on C H .…”

Stable protocrystalline silicon and unstable microcrystalline silicon at the onset of a microcrystalline regime

“…Not all hydrogen dilution techniques increase hydrogen content; it has been reported that hydrogen dilution can decrease C H . 12 Our results also show that the amount of degradation has no dependence on C H . At the onset of the microcrystalline regime, we observed two types of Si-H stretching modes in the FTIR spectrum.…”

Film growth precursors in a remote SiH4 plasma used for high-rate deposition of hydrogenated amorphous silicon

“…In this respect, one of the central questions is whether it is possible to deposit a-Si:H suitable for the application in thin solar cells at high growth rates (preferablyϾ1 nm/s). Several investigations have already addressed this question, [1][2][3][4][5][6][7][8][9][10] and recently it was shown that device-quality a-Si:H can be obtained even at a rate of 10 nm/s with the expanding thermal plasma. 11,12 This technique combines a high-pressure thermal plasma source with a low-pressure deposition chamber and is, therefore, a real remote plasma.…”