Oxide Scalability Characteristics in MBE grown Al2O3/Ga2O3(Gd2O3)/In0.2Ga0.8As/GaAs MOS Capacitors and ALD-Al2O3/In0.2Ga0.8As/GaAs MOSFET : ALD Growth, Processing, and Characteristics

Abstract

Part (I): Oxide Scalability An equivalent oxide thickness about 1 nm for molecular beam epitaxy (MBE)-grown Ga2O3(Gd2O3) (GGO) on In0.2Ga0.8As has been achieved by employing a thin in situ deposited 3 nm thick Al2O3 protection layer. The novel hetero-structures are robust electrically and structurally with rapid thermal annealing (RTA) to high temperatures of 800-850°C under N2 flow. Furthermore, the dual gate oxide stacks of the Al2O3/GGO (33, 20, 10, 8.5, and 4.5 nm)/In0.2Ga0.8As/GaAs metal-oxide-semiconductor (MOS) capacitors remain amorphous after RTA up to 800-850°C, accompanied with atomically sharp smooth oxide/semiconductor interfaces and fully strained In0.2Ga0.8As/GaAs interface without lattice relaxation. Well behaved capacitance-voltage (C-V) curves of the MOS diodes have shown sharp transition from depletion to accumulation with small flatband voltage (1.1 V for Au metal gate and 0.1 V for Al), weak frequency dispersion (1.5%–5.4%) between 10 and 500 kHz at accumulation capacitance, and small hysteresis (116-170 mV) at half accumulation capacitance of 100 kHz. The observed inversion formation in the C-V characteristics under light illumination or quasi-static mode explicitly confirmed that the Fermi level is effectively unpinned by the GGO passivation approach. Low leakage current densities (3.1×10−5 and (10−8-10−9) A/cm2 at V=Vfb+1 V for Al2O3(3 nm)/GGO(4.5 and ≧8.5 nm), a high dielectric constant around 14-16 of GGO for all tested thicknesses, and a low interfacial density of states (Dit) in the low 1011 cm−2 eV−1 have also been accomplished. Keywords: molecular beam epitaxy, high-□ gate dielectric, III-V, MOS, oxide scaling, Ga2O3(Gd2O3), Al2O3, InGaAs, RTA. Part (II): GaAs-based MOSFET Well-behaved electrical characteristics of D-mode n-channel In0.2GaA0.8/GaAs MOSFETs with 4.5 nm thick atomic layer deposition (ALD)-grown Al2O3 as gate dielectric by using ring-gate process have been demonstrated, achieving a drain current of 33 mA/mm (at Vg=2.5V and Vd=3V), and a transconductance of 16 mS/mm (at Vg=-0.2V and Vd=2.5V) with a 8 □m-gate-length and a 200 □m-gate-width. TiN and Au/Ti were chosen as metal gates during device fabrication due to the suitable thermal stability and workfunction respectively. This demonstration also successfully extends our ALD-Al2O3/In0.2GaA0.8/GaAs material system to a realized MOSFETs device for the first time. The application of ring-gate process was established as a feasible approach to rapidly examine/calibrate the high □/III-V materials systems due to its simplicity in processing steps, consisting of gate metal and S/D contact metal formations without isolation step, and further enable to embody the MOSFETs operation. Furthermore, the nm-thin oxide layer (4.5 nm Al2O3) with extremely low gate leakage current densities around 8.06×10-9 A/cm2 at 1 MV/cm from a 8 □m-gate-length device have also been achieved, that symbols one of the key capabilities of ALD-Al2O3 in downsizing field-effect transistors. Keywords: MOSFET, atomic layer deposition, high-□ gate dielectric, metal gate, III-V, Al2O3, InGaAs, GaAs