No abstract

In a previous work [1], the deposition conditions that provided low optical absorption related to both band tail and deep localized states have been found for both materials Ge:H and Si 1-Y Ge Y :H. In this work phosphorous and boron doping of Ge:H films have been systematically studied. These films were deposited by low frequency (LF) plasma under the conditions for low density of localized states whit optimal hydrogen dilution. The deposition parameters were as follow: substrate temperature Ts= 300 °C, discharge frequency f= 110 kHz, pressure P= 0.6 Torr, power W= 300 W, and the flow gas for the films of Ge:H was; germane flow QGeH 4 = 50 sccm, hydrogen flow QH 2 =2500 sccm, the phosphine flow was varied in the range of QPH 3 = 20 to 100 sccm providing phosphorous concentration in gas phase in the range of X P = 4 to 20 %. For boron we used the same conditions as before, but the B 2 H 6 flow was varied in the range of QB 2 H 6 = 3 to 20 sccm providing concentration in gas phase in the range of X B = 0.3 to 4 %. SIMS profiling was used for determining the composition of the doped films. The hydrogen bonding was studied by FTIR. The temperature dependence of conductivity measured in DC regime was performed in a vacuum thermostat in order to study carrier transport. Optical measurements provided optical gap, absorption and refraction index. The Phosphorous incorporation to the solid film demonstrated that for the doping conditions used in this work, we obtained a constant P concentratio. But for boron incorporation, the concentration of it in the solid films increases linearly with its concentration in the gas phase. The influence of the P and B doping on the hydrogen concentration, activation energy and conductivity of the films is also studied and presented.

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%.

Deposition conditions that provided low absorption related to both band tail and deep localized states have been found for both materials Ge:H and Si1YGeY:H. Phosphorous incorporation on Si0.01Ge0.99:H films and boron incorporation on Ge:H films were deposited by low frequency plasma-enhanced chemical vapour deposition (LF PECVD). The phosphorous incorporation in solidphase was observed to preferential with the increase of the doping in the gas phase to 2.5 %, and 2.5% to 4% was observed preferential Si0.01Ge0.99 film, boron incorporation in solid phase increase linearly with the increase of the doping gas phase. The content of solid phase was characterized by Secondary ion mass spectrometry (SIMS) profiling. Hydrogen concentration in the films was determined from Fourier transform infrared spectroscopy (FTIR) and SIMS measurements. Optical measurements provided optical gap, localized states, and band tail. A significant reduction of both band tail and deep localized states were observed at boron incorporation in solid phase = 0.004% on Ge:H films and the same were observed at phosphorous incorporation in solid phase = 0.29% on Si0.01Ge0.99:H films.