Low temperature growth of highly conductive boron-doped germanium thin films by electron cyclotron resonance chemical vapor deposition

The effect of the doping ratio (B₂H₆/GeH₄) on the structural and electrical properties of boron doped hydrogenated germanium films deposited by the electron cyclotron resonance chemical vapor deposition process has been investigated. By increasing the flow rate of B ₂H₆/GeH₄ from 0.025 to 0.125, more boron related radicals are available to desorb hydrogen atoms from the growing surface. This leads to degradation of the structure of the amorphous phase identified by Raman and X-ray diffraction spectroscopy. The incorporation of boron enhances the carrier concentration from 1.65 × 10¹⁹ cm^{- 3} to 2.25 × 10²⁰ cm^{- 3} and reduces the resistivity from 0.131 ·cm to 0.018 ·cm as measured by Hall measurement. These highly conductive boron-doped hydrogenated Ge films can be useful as low resistance doped layer in devices to achieve better performance. Moreover, we are able to deposit highly conductive boron-doped Ge films at a low growth temperature (180 C) and low hydrogen dilution ratio (H ₂/GeH₄ = 33), in this study. Such a low temperature process can overcome some problems with high temperature deposition process that limit application in devices. Furthermore, the low hydrogen dilution ratio can minimize an ion bombardment effect on the films.