Positive Charge in SOS Heterostructures with Interlayer Silicon Oxide

Abstract

The continuous transfer of (001)Si layers 0.2–1.7 μm thick by implanted hydrogen to the c-sapphire surface during direct bonding at high temperatures of 300–500°C is demonstrated for the first time. The formation of an intermediate silicon-oxide layer SiO_x during subsequent heat treatments at 800–1100°C, whose increase in thickness (up to 3 nm) correlates with an increase in the positive charge Q_i at the heterointerface to ~1.5 × 10¹² cm^–2 in contrast to the negative charge at the SiO_x/Al₂O₃ ALD heterointerface. During silicon-layer transfer to sapphire with a thermal silicon-dioxide layer, Q_i decreases by more than an order of magnitude to 5 × 10¹⁰ cm^–2 with an increase in the SiO₂ thickness from 50 to 400 nm, while the electron and hole mobilities barely differ from the values in bulk silicon. Based on these results, a qualitative model of the formation of positively charged oxygen vacancies in a 5-nm sapphire layer near the bonding interface is proposed.