Si/Ge Junctions Formed by Nanomembrane Bonding

Abstract

We demonstrate the feasibility of fabricating heterojunctions of semiconductors with high mismatches in lattice constant and coefficient of thermal expansion by employing nanomembrane bonding. We investigate the structure of and electrical transport across the interface of a Si/Ge bilayer formed by direct, low-temperature hydrophobic bonding of a 200 nm thick monocrystalline Si(001) membrane to a bulk Ge(001) wafer. The membrane bond has an extremely high quality, with an interfacial region of ∼1 nm. No fracture or delamination is observed for temperature changes greater than 350 °C, despite the approximately 2:1 ratio of thermal-expansion coefficients. Both the Si and the Ge maintain a high degree of crystallinity. The junction is highly conductive. The nonlinear transport behavior is fit with a tunneling model, and the bonding behavior is explained with nanomembrane mechanics.

Comprehensive investigation of Ge–Si bonded interfaces using oxygen radical activation

“…Recently the I-V behavior at the Si-Ge hetero-interface has been reported using 200 nm n þ -Si (4 Â 10 20 /cm 3 ) bonded to a p þ -Ge (1 Â 10 20 /cm 3 ) wafer, which is similar to the doping profile of our device structure. 16 As comparison, our measured current flow through bonded the hetero-junction appears to be similar to plots shown in Ref. 16.…”

“…16 As comparison, our measured current flow through bonded the hetero-junction appears to be similar to plots shown in Ref. 16. The depletion layer width for p-type Ge/n þ -type Si hetero-junction is considerably narrower than those of conventional p-n junction, which enables the carriers to tunnel across the interface.…”

“…It is known that hydrophobic bonding produces less oxide at the interface which will results in higher conductivity cross the bonded interface. 16 However, the 2 nm amorphous interface is small enough to allow conductivity by means of tunneling. Consequently our hydrophilic direct wafer bonding using oxygen radical exposure is feasible for fabrication of a Ge-Si p-n junction.…”

Characterization of germanium/silicon p–n junction fabricated by low temperature direct wafer bonding and layer exfoliation

“…Thus, the leakage current density is relatively temperature independent and the conduction mechanisms are likely to be direct and band-toband tunnelling through the interfacial oxide rather than generation-recombination mechanism. 10 This can also be confirmed by the improvement of the diode ideality factor after the heat treatment (see Fig. 2(a)).…”

“…More recently, Si/Ge junctions were fabricated by nanomembrane bonding where the junction is dominated by Fowler-Nordheim tunnelling leakage current. 10 In this letter, we perform a proof of concept of p-Ge/n-Si integration by using wafer bonding and layer exfoliation with a low thermal budget followed by the fabrication, characterisation, and analysis of the electrical transport across the interfacial oxide which is present between the p-Ge and n-Si regions.…”