Enhancement of electrical performance of Ge-based metal-oxide-semiconductor capacitor via formation of trigonal-Sm2O3

Abstract

In this study, Sm2O3/Ge stack based capacitor prepared from thermally oxidized/nitrided sputtered metallic Sm on Ge semiconductor in N2O ambient for several oxidation/nitridation durations, i.e., 5 – 20 min have been comprehensively investigated. The film crystallinity, chemical composition and interface chemical bonding states stability was characterized from X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). Formation of trigonal-Sm2O3 dielectric interface together with an interfacial layer containing asymmetrically distributed (GeO, SmOGe and GeN) species has been verified. Suppression of GeO (g) volatilization was evident from the XPS analysis due to germanate (SmOGe) formation. Structural morphology characterization using high resolution transmission electron microscope (HRTEM) also validated double stack amorphous interfaces obtaining physical oxide thickness (tox) from 4.25 − 6.91 nm. Band alignment and electrical measurements revealed that oxidation/nitridation duration of 15 min exhibited highest conduction band offset (CBO), ΔEc of 2.60 eV and valence band offset (VBO) ΔEv of 2.98 eV leading to lowest leakage current density Jg∼ 8.38 × 10−6 A cm−2 at enhanced breakdown field, EBD of 13.31 MV cm−1. The large breakdown field has been ascribed to fewest effective oxide charge (Qeff), slow trap density, (Qit) and interface traps density Dit at this duration. Additionally, a low equivalent oxide thickness, tEOT∼ 0.75 nm with a high dielectric constant k∼ 31.19 eV was achieved but with a price of high Dit∼ 1013 eV−1cm−2. These properties render that Sm2O3 could serve as dielectric material for future high-k/Ge stack based metal oxide semiconductor technology, although requires further investigation for Dit improvement.