Thermal Annealing Study of Variable Band-Gap a-SiN:H Alloy Films
- PDF / 116,538 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 11 Downloads / 140 Views
Thermal Annealing Study of Variable Band-Gap a-SiN:H Alloy Films N. Banerji, E. Faro1 and J.Serra Dpto. Física Aplicada, Univ. de Vigo, Lagoas-Marcosende, 36200 Vigo, Spain 1 Dpto. Matemática Aplicada, Univ. de Vigo, Lagoas-Marcosende, 36200 Vigo, Spain ABSTRACT A study of the effects of thermal annealing on the bond structure, optical properties, morphology and stoichiometry of variable band gap a-SixNyHz alloy films deposited by ArF LCVD has been made. These films were generated through two different photochemical pathways resulting from the use of either SiH4/NH3 or Si2H6/NH3 as precursor gases. Thermal annealing study of these films which span a wide compositional (0.22 < x/y < 1.44) and band-gap (Eg) range (1.7−5.2 eV) has led to the analysis of the stability of different bond configurations. We report here hydrogen bond stability and rearrangement of the near-neighbor environment of SiN bonds analyzed through FTIR, refractive index variations measured by ellipsometry and surface morphological changes observed through AFM during to the process of annealing. Results indicate that in the SiH4/NH3 deposited nitrogen-rich SiN:H films, SiHn bonds persist even upto 900ºC and SiH bonds are less thermally stable than SiH2. Also, while the total bonded hydrogen decreases, the extent of SiN bond increases through a reaction mechanism involving: SiH + NH → SiN + H2. In the Si2H6/NH3 deposited silicon-rich film, whose initial spectra shows Si-H stretching and Si-H wagging bands, a rapid loss of Si-H bonds occurs at T ≤ 650ºC. Based on the bond configurational interpretations of the Random bonding model proposed by Bustarret, we calculate the variations in film stoichiometry and density with the annealing temperature. INTRODUCTION Recently, applications of a-SixNyHz alloys for the electronic industry have broadened with the possibilities of obtaining thin films of this material with a wide-mobility gap [13]. For [N]/[Si] ratios less than ∼1.0, the material behaves like a wide band-gap variety of amorphous silicon showing Eg variability between 1.6 - ∼ 3.0 eV [4]. Such material has found applications for its semiconducting properties in optoelectronic devices [1, 2]. For higher [N]/[Si] ratios, the band-gap opens up sharply with increasing nitrogen concentration reaching up to ~ 5 eV; being this the compositional range where such films have been conventionally used for their passivating and insulating behavior [5]. We have obtained silicon-rich and nitrogen-rich a-SixNyHz alloy films by ArF LCVD at low temperatures (T ≤ 350ºC) using silane/ammonia or disilane/ammonia as the precursor gas mixtures. By systematically monitoring the deposition parameters we have obtained, using silane/ammonia mixtures, [N]/[Si] variability between 0.29 - 1.44 and Eg variability between 2.2 – 5.2 eV. With disilane/ammonia mixture, we have so far obtained films whose compositions are below the percolation threshold for Si-Si bonds (0.22 < [N]/[Si] < 0.72 ). However, within this range of Eg variability, it has been possible to finely tailor the ga
Data Loading...
