Density and Capture Cross-Section of Interface Traps in GeSnO₂ and GeO₂ Grown on Heteroepitaxial GeSn

Abstract

An imperative factor in adapting GeSn as the channel material in CMOS technology, is the gate-oxide stack. The performance of GeSn transistors is degraded due to the high density of traps at the oxide-semiconductor interface. Several oxide-gate stacks have been pursued, and a midgap Dit obtained using the ac conductance method, is found in literature. However, a detailed signature of oxide traps like capture cross-section, donor/acceptor behavior and profile in the bandgap, is not yet available. We investigate the transition region between stoichiometric insulators and strained GeSn epitaxially grown on virtual Ge substrates. Al2O3 is used as high-κ oxide and either Ge1-xSnxO2 or GeO2 as interfacial layer oxide. The interface trap density (Dit) profile in the lower half of the bandgap is measured using deep level transient spectroscopy, and the importance of this technique for small bandgap materials like GeSn, is explained. Our results provide evidence for two conclusions. First, an interface traps density of 1.7 × 10(13) cm(-2)eV(-1) close to the valence band edge (Ev + 0.024 eV) and a capture cross-section (σp) of 1.7 × 10(-18) cm(2) is revealed for GeSnO2. These traps are associated with donor states. Second, it is shown that interfacial layer passivation of GeSn using GeO2 reduces the Dit by 1 order of magnitude (2.6 × 10(12) cm(-2)eV(-1)), in comparison to GeSnO2. The results are cross-verified using conductance method and saturation photovoltage technique. The Dit difference is associated with the presence of oxidized (Sn(4+)) and elemental Sn in the interfacial layer oxide.

Correlation of Bandgap Reduction with Inversion Response in (Si)GeSn/High-k/Metal Stacks

“…All samples feature low dispersion in accumulation (here negative bias voltages) and small frequency-dependent flat band voltage shift, indicating good interface quality with the high-k dielectrics. This is supported by measurements of the interface trap densities, with a D it of about 2 × 10 12 cm –2 eV –1 , in agreement with literature reports. ,− For voltages between −0.5 and 0 V the so-called weak inversion hump appears, pointing toward an enhanced interaction of traps with both conduction and valence bands. However, this hump is not a sign of a high D it but is a characteristic of low band gap semiconductor MOSCaps .…”

“…In order to exclude the impact of series resistance on CV-characteristics a correction of the measured capacitance Cm and parallel conductance Gm has been applied, as proposed by Nichollian and with the high-k dielectrics. This is supported by measurements of the interface trap densities, with a Dit of about 2x10 12 cm -2 eV -1 , in agreement with literature reports 12,[16][17][18] . For voltages between -0.5 V and 0 V the so-called weak inversion hump appears, pointing towards an enhanced interaction of traps with both conduction and valence bands.…”

Optically pumped GeSn micro-disks with 16% Sn lasing at 3.1 μm up to 180 K

“…Germanium tin (GeSn) is a Complementary Metal Oxide Semiconductor (CMOS)-compatible group IV material which can exhibit a direct bandgap [1,2], leading to potential applications in photonics [3] and microelectronics [4]. Recent progresses in Chemical Vapor Deposition (CVD) [5] allowed the demonstration of the first GeSn laser in 2015 [3].…”

Raman spectral shift versus strain and composition in GeSn layers with 6%–15% Sn content

“…GeSn is a very interesting group IV material which presents a direct bandgap (predicted since the eighties 1,2 ) that could be most interesting for photonics 3 or microelectronics applications 4 .…”