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Effect of phosphorus incorporation in hydrogenated amorphous silicon

Amer Brighet 1Rabah Cherfi 1Mohamed Kechouane 1Abdelmadjid Abdelmoumen 1,2

1. Laboratoire "Couches Minces et Semiconducteurs" - USTHB - Faculté de Physique -, BP 32 El-Alia - Bab-Ezzouar, Alger 16111, Algeria
2. Centre de Developpement des Technologies Avancées (CDTA), BP17, Lot. 20 Aout 1956, Baba Hassen, Alger 16000, Algeria


The effects of the phosphorus incorporation on physical, chemical, optical and electric properties of phosphorus-doped hydrogenated amorphous silicon thin films (a-Si:H(P)) are presented. Doping was carried out from the use of a nontoxic phosphorus liquid source based on hydrocarbons (trimethylphosphine: TMP, (P (CH3) introduced into the deposit chamber by using hydrogen as carrying gas.

The a-Si:H films (0.7-1.0 mm thick) were deposited by the DC magnetron sputtering of a silicon target under hydrogen and argon plasma at various TMP partial pressures between 0 to 9.10-5 mbar. The a-Si:H(P) were characterized by secondary ion mass spectrometry (SIMS), infrared absorption, optical transmission and electrical conductivity measurements.
The infrared   absorption at 670 cm-1 can be attributed to the P-H bonds. The effect of TMP partial pressure can be observed through the broadening of the 2000 cm-1 band and a displacement towards the high frequencies. The phosphorus incorporation in a-Si:H matrix was confirmed by secondary ion mass spectrometry (SIMS) measurements.

Optical transmission measurements are used in order to determine the refractive index nS and the optical gap ET.  The increase of ET can be explained by carbon/silicon alloy effect and the variation in refractive index is indicative of material structure change.

The effect of annealing temperature on electrical conductivity was also studied. The results concerning the variation of electrical conductivity under darkness and photoconductivity, respectively σd and σph, according to the annealing temperature Ta clearly evidenced an increase in conductivity with Ta in the range of 130 - 225° C. The increase of conductivity with annealing can be explained by the increase in the doping effectiveness through the activation of the phosphorus atoms in the silicon matrix. The decrease of Ea can be related to the shift of the Fermi level towards the conduction band due to phosphorus doping.


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Presentation: Poster at E-MRS Fall Meeting 2008, Symposium B, by Mohamed Kechouane
See On-line Journal of E-MRS Fall Meeting 2008

Submitted: 2008-05-14 15:42
Revised:   2009-06-07 00:48