Amorphous silicon-germanium (a-Si 0.01 Ge 0.99 :H) doped with phosphorous deposited by LF PECVD and its electrical and o
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Amorphous silicon-germanium (a-Si0.01Ge0.99:H) doped with phosphorous deposited by LF PECVD and its electrical and optical characteristics N. Delgadillo1, A. Kosarev2, A. Torres2, and B. Gonzales1. 1 Electronics Systems, University Autonomous of Tlaxcala, Calzada Apizaquito, Km. 1.5, Apizaco, Tlaxcala, 93000, Mexico. 2 Electronics, National Institute for Astrophysics, Optics and Electronics, L.E. Erro No.1, Tonantzintla, Puebla, 72840, Mexico. ABSTRACT Amorphous silicon-germanium (a-Si0.01Ge0.99:H) thin film, practically amorphous germanium with small concentration of silicon, were deposited by the low frequency PECVD technique under different flow gas of phosphine in the range of QPH3 = 20 to 100 sccm. In this range the phosphorous concentration in gas phase was calculated as XP= 4 to 20 % which resulted in a content in solid phase [P]sol=0.12% - 0.4%. The P content of the solid phase was measured by SIMS profiling and it was also observed a preferential incorporation of phosphorous in the range of [P]sol=0.12% - 0.3%. Hydrogen concentration in the films was determined from FTIR and SIMS measurements. The activation energy was determined by measuring the temperature dependence of conductivity in DC regime in a vacuum thermostat. For the a-Si0.01Ge0.99:H films it is found that the activation energy have a minimum, (Ea= 0.15eV), its conductivity at room temperature have a maximum and there is a minimum of of both band tail and deep localized state for a phosphorous incorporation in solid phase [P] =0.28%.
INTRODUCTION The alloy system of hydrogenated amorphous silicon germanium films (a-SiyGe1became an attractive one because it offers the possibility of varying its band gap with the germanium content and as a result, improves its optical response to larger wavelengths for applications in solar cells and photovoltaic devices [1-2]. Extensive research on hydrogenated amorphous silicon–germanium films has been carried out using various techniques for preparing a competitive material in many applications. This material as thin film may be deposited by the plasma-enhanced chemical vapour deposition technique (PECVD) or by DC magnetron sputtering [3-4]. A typical excitation frequency used in the deposition of the amorphous silicon-germanium by the PECVD technique is 13.56 MHz [5]. However when low frequency (LF) is used as the excitation frequency in the PECVD, the system allows conditions in which the film being deposited is subjected to a high ion bombardment [6-7]. The germanium content in the film is itself a function of temperature and of the ratio of the germane to silane gas flow. Therefore, the deposition of a-SiGe:H is a complex function of temperature, pressure and germane and silane partial pressures, and y:H),
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has been studied extensively [8]. In this work we determine the deposition rate, the phosphorous incorporation, the hydrogen concentration, the electrical and optical properties of the films and the effect of small concentration of silicon on the a-SiyGe1-y:H in films obtained using the low freque
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