Interface Properties Of Gap/Si Heterojunction Fabricated By Pe-Ald

The properties of n-GaP/p-Si interface as well as their influence on solar cell performance are studied for GaP layers grown by low-temperature (380 degrees C) plasma-enhanced atomic layer deposition (PE-ALD). The influence of different plasma treatments and RF power values are explored. The increase of RF power leads to a growth transition from amorphous (a-GaP) to microcrystalline GaP (mu c-GaP) with either amorphous-GaP/Si or epitaxial-GaP/Si interface, respectively. However, when continuous hydrogen plasma is used the amorphous-GaP/Si interface exhibits better photovoltaic performance compared to the epitaxial one. Values of open circuit voltage, V-oc = 0.45-0.55 V and internal quantum efficiencies, IQE > 0.9 are obtained for amorphous-GaP/Si interfaces compared to V-oc = 0.25-0.35 V and IQE < 0.45 for epitaxial-GaP/Si interfaces. According to admittance spectroscopy and TEM studies the near-surface (30-50 nm) area of the Si substrate is damaged during growth with high RF power of hydrogen plasma. A hole trap at the level of E-V + (0.33 +/- 0.02) eV is detected by admittance spectroscopy in this damaged Si area. The damage of Si is not observed by TEM when the deposition of the structures with epitaxial-GaP/Si interface is realized by a modified process without hydrogen plasma indicating that the damage of the near-surface area of Si is related to hydrogen plasma interaction.