GaAs to Si Direct Wafer Bonding at T <= 220 degrees C in Ambient Air Via Nano-Bonding (TM) and Surface Energy Engineering (SEE)

When different semiconductors are integrated into hetero-junctions, native oxides generate interfacial defects and cause electronic recombination. Two state-of-the-art integration methods, hetero-epitaxy and Direct Wafer Bonding (DWB), require temperatures, T > 400 degrees C to reduce native oxides. However, T > 400 degrees C leads to defects due to lattice and thermal expansion mismatches. In this work, DWB temperatures are lowered via Nano-Bonding (TM) (NB) at T <= 220 degrees C and P <= 60 kPa (9 psi). NB uses Surface Energy Engineering (SEE) at 300 K to modify surface energies (gamma(T)) to far-from-equilibrium states, so cross-bonding occurs with little thermal activation and compression. SEE modifies gamma(T) and hydro-affinity (HA) via chemical etching, planarization, and termination that are optimized to yield 2-D Precursor Phases (2D-PP) metastable in ambient air and highly planar at the nano- and micro- scales. Complementary 2D-PPs nano-contact via carrier exchange from donor 2D-PP surfaces to acceptor ones. Here, NB models and SEE are applied to the DWB of GaAs to Si for photovoltaics. SEE modifies (1) the initial gamma(T0) and HA(0) measured via Three Liquid Contact Angle Analysis, (2) the oxygen coverage measured via High Resolution Ion Beam Analysis, and (3) the oxidation states measured via X-Ray Photoelectron Spectroscopy. SEE etches hydrophobic GaAs oxides with gamma(T) = 33.4 +/- 1 mJ/m(2), and terminates GaAs (100) with H+, rendering GaAs hydrophilic with gamma(T) = 60 +/- 2 mJ/m(2). Similarly, hydrophilic Si native oxides are etched into hydrophobic SiO4H2. H+- GaAs nano-bonds reproducibly to Si, as measured via Surface Acoustic Wave Microscopy, validating the NB model and SEE design.