Silicon Surface Passivation with a-Si:H and epi-Si Layer—Effects of Plasma-induced Defects and Interface Structure

The surface passivation of crystalline silicon (c-Si) is important for the optoelectronic devices such as solar cell and image sensor. The passivation is usually obtained by the formation of wide-gap materials over the c-Si surface. Among them, hydrogenated amorphous silicon (a-Si:H), prepared by plasma enhanced chemical vapor deposition (PECVD), is known to yield an excellent property of passivation, however, the defect creation and band structure at the a-Si:H/c-Si interface is not fully understood.<br/>In this presentation, we show the surface passivation during growth of a-Si:H and epitaxial silicon (epi-Si), in terms of the defect creation as well as band structure [1]. To do that, the growth mode of the passivation layer is changed from epitaxial to amorphous, by controlling the hydrogen dilution during PECVD. The passivation property is monitored in real time via the photocurrent measurement of c-Si during PECVD and post-annealing [2].<br/>We find the following results [1]. For the a-Si:H growth over c-Si, the passivation is maximized via the formation of a large valence band offset at the a-Si:H/c-Si interface. For the epi-Si layer growth, the passivation is deteriorated with an ultrathin layer of epi-Si, because the H-mediated defects are created in the c-Si bulk near the surface. In addition, the band bending is not fully formed near the epi-Si/SOI interface. Thus, the suppression of the bulk Si defects as well as the formation of the band offset are important for the passivation.<br/>[1] S. Nunomura <i>et al</i>., J<i>. Appl. Phys</i>. <b>128</b>, 033302 (2020).<br/>[2] S. Nunomura <i>et al.</i>, <i>Appl. Phys. Exp</i>. <b>12</b>, 051006 (2019).