The stability of metallized, thin, flexible III–V structures for high temperature applications and wafer bonding

Abstract

The stability of thin, flexible III-V layers / solar cells with metallization was addressed. Reduced cell thickness (reduced weight) places added constraints on metallization sequences, thicknesses, and thermal budgets for these cells. We subjected a structure of a thin (few μm) III-V layers (the focus here is on InP-based structures) with metallization backing (Au, Ni, and Cu-based metallizations, several μm thick) to annealing at 200 °C, 300 °C, or 400 °C for up to a twelve hours. X-ray diffraction is a particularly useful technique as measurements from the solar cell (semiconductor) side of the stack also reveals the metallization diffraction peaks and hence any reaction byproducts. This is due to the beam penetration through the few μm thick cell layers. After 200 °C for twelve hours, x-ray diffraction and transmission electron microscopy indicate reactions between the metal layers in the stack but the semiconductor is unchanged. After 300 °C, twelve hours, there is more extensive intermetallic compound formation. However, after annealing at 400 °C, twelve hours, the III-V layer is entirely consumed. In contrast, when much thicker cells / semiconductor layers are subject to similar annealing conditions, there may not be a significant impact on performance because only a few μm of the total cell thickness is consumed. When the total thickness is only a few μm, however, the reaction between the metal contact layer and the semiconductor leads to consumption of the entire device. These results demonstrate that (i) the total cell thickness is important when considering contact-semiconductor interactions at elevated operating or processing temperatures and (ii) x-ray diffraction through the thin cell provides a detailed assessment of reactions; it can be utilized for any combination of thin film solar cell and metallization.