(Invited) Preparation of GaSb Surface for Low Interfacial Trap Density MOS Capacitors

High mobility III-V compound semiconductors have been extensively investigated recently for future complementary metal-oxide-semiconductor (CMOS) applications. GaSb, which has high electron and hole mobilities as well as a narrow bandgap is an attractive material for future high-speed and low-power integrated circuits. Due to the easy formation of native oxides, i.e. SbO_x, GaO_x, and elemental Sb clusters on GaSb surface, Fermi-level pinning and high interfacial trap density (D_it) has been a major obstacle to high quality MOS devices. In this talk, we will present both in-situ and ex-situ techniques to prepare GaSb surface and realize metal-oxide-semiconductor capacitors (MOSCAPs) with low interfacial trap density.

The in-situ approach is conducted in a system equipped with a high vacuum sample transfer tube that connects a molecular beam epitaxy (MBE) tool and an atomic layer deposition (ALD) chamber. A native oxide-free surface can thus be preserved for high-κ dielectrics deposition. HfO₂/Al₂O₃/GaSb MOSCAPs fabricated on Sb-stabilized surface exhibit clear inversion behavior at low frequency and good modulation of the Fermi level across the whole GaSb band gap. Modulation of the inversion capacitance at 100 kHz reaches 30 %, suggesting low D_it as well as low bulk trap density at the interface. The D_it extracted by the conductance method is about 7.6×10¹¹ cm^-2eV^-1 near the valence band. As to the ex-situ process, air-exposed GaSb samples are treated by hydrogen plasma at room temperature prior to ALD dielectrics. Under optimized plasma treatment conditions, similar C-V characteristics and gate leakage current of HfO₂/Al₂O₃/GaSb MOSCAPs to those of the in-situ ones are observed. Modulation of the inversion capacitance at 100 kHz even reaches 36 % and the D_it near the valence band is as low as 6.0×10¹¹ cm^-2eV^-1.

Structural and chemical analyses of the dielectric/semiconductor interface by high-resolution transmission electron microscopy (HRTEM) and x-ray photoelectron spectroscopy (XPS) show that the in-situ MOSCAPs have a native oxide-free interface, while hydrogen plasma treatment results in the formation of GaO_x, which may serve to passivate defects and dangling bonds at the GaSb surface