Highly Conducting Phosphorous Doped nc-Si:H Thin Films Deposited at High Deposition Rate by Hot-Wire Chemical Vapor Deposition Method

Abstract

In this paper, we report the synthesis of highly conducting phosphorous doped hydrogenated nanocrystalline silicon (nc-Si:H) films at substantially low substrate temperature (200 degrees C) by hot-wire chemical vapor deposition (HW-CVD) method using pure silane (SiH4) and phosphine (PH3) gas mixture without hydrogen dilution. Structural, optical and electrical properties of these films were investigated as a function of PH3 gas-phase ratio. The characterization of these films by low-angle X-ray diffraction, Raman spectroscopy and atomic force microscopy revealed that, the incorporation of phosphorous in nc-Si:H induces an amorphization in the nc-Si:H film structure. Fourier transform infrared spectroscopy analysis indicates that hydrogen predominately incorporated in phosphorous doped n-type nc-Si:H films mainly in di-hydrogen species (Si-H2) and poly-hydrogen (Si-H2)n bonded species signifying that the films become porous, and micro-void rich. We have observed high band gap (1.97-2.37 eV) in the films, though the hydrogen content is low (< 1.4 at.%) over the entire range of PH3 gas-phase ratio studied. Under the optimum deposition conditions, phosphorous doped nc-Si:H films with high dark conductivity (sigma Dark -5.3 S/cm), low charge-carrier activation energy (E(act) - 132 meV) and high band gap (- 2.01 eV), low hydrogen content (- 0.74 at.%) were obtained at high deposition rate (12.9 angstroms/s).

Superior Phosphorous Doping in Nanocrystalline Silicon Thin Films and Their Application as Emitter Layers in Silicon Heterojunction Solar Cells

“…A comparative analysis correlating the optical band gap with the dark conductivity of the present n -nc-Si thin film with the other reported materials is represented in Figure . A similar enhancement in dark conductivity and narrowing in the optical band gap after P doping was also previously reported by Waman et al , Conductivity in the range 1.1–5.3 S cm –1 , with an associated band gap of 2.07–2.17 eV, was attained in the n -nc-Si thin film grown in HWCVD. Without H 2 -dilution, Song et al prepared a mostly amorphous as-deposited doped film with a low dark conductivity of ∼3.4 × 10 –4 S cm –1 and an optical band gap of ∼1.84 eV.…”

Synthesis and Characterization of Phosphorus Doped Hydrogenated Silicon Films by Filtered Cathodic Vacuum Arc Technique

“…In thin film solar cells, due to higher mobility, reduced light induced degradation [5] and enhanced absorption in the near infrared wavelength range, nc-Si significantly exhibits higher energy conversion efficiencies than amorphous silicon. So far, the production of nc-Si thin films have been focused on some deposition techniques such as plasma enhanced chemical vapor deposition (PECVD), hot wire chemical vapor deposition (HWCVD), inductively coupled plasma enhanced chemical vapor deposition (IC-PECVD) [6][7][8][9][10] etc. by decomposing monosilane or disilane gas.…”