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Effects of boron and phosphorus incorporation in hydrogenated amorphous silicon
|Amer Brighet 1, Nabil Khelifati 1, Rabah Cherfi 1, Mohamed Kechouane 1, Abla Rahal 1, Abdelmadjid Abdelmoumen 1, Aissa Keffous 2, Moussa Aoucher 1|
1. Laboratoire "Couches Minces et Semiconducteurs" - USTHB - Faculté de Physique -, BP 32 El-Alia - Bab-Ezzouar, Alger 16111, Algeria
The effects of boron and phosphorus incorporation on physical, chemical, optical and electric properties of boron and phosphorus-doped hydrogenated amorphous silicon thin films (a-Si:H(B), a-Si:H(B)) are presented. Boron was incorporated into the host material by a DC magnetron co-sputtering technique. Phosphorus doping was carried out from of a non-toxic phosphorus liquid source based on hydrocarbons (trimethylphosphine: TMP, (P (CH3) by using hydrogen as carrying gas.
a-Si:H(B) and a-Si:H(P) films at various hydrogen and TMP partial pressures were characterized by secondary ion mass spectrometry (SIMS), infrared absorption, optical transmission and electrical conductivity measurements.
SIMS measurements clearly showed evidence for boron incorporation. This boron incorporation induced an increase of the refractive index and a decrease of the optical gap. The infra-red analysis showed that hydrogen lies preferentially to silicon that with boron.
For a-Si:H(B) films, the increase of the hydrogen partial pressure induced an increase of the Si-H stretching and wagging band at 2000 and 640 cm-1 followed by a decrease of the Si-B and/or B-B stretching band at 700-900 cm-1, accompanied by an increase of the optical gap and by an important reduction of electrical conductivity under darkness. The hydrogen is crucial for stability of the films; it plays the role as passivator for boron atoms where electrical activation takes place for the annealing temperature range between 200 and 350°C.
For a-Si:H(P) films, 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. The increase of optical gap is related to carbon/silicon alloy effect and the variation of refractive index is indicative of material structure change. The conductivity increase with annealing is related to an increase of the doping effectiveness through the phosphorus activation in the silicon matrix.
Presentation: Poster at E-MRS Fall Meeting 2008, Symposium B, by Mohamed Kechouane
See On-line Journal of E-MRS Fall Meeting 2008
Submitted: 2008-06-30 16:35 Revised: 2009-06-07 00:48