Process Modules for GeSn Nanoelectronics with high Sn-contents

This paper systematically studies GeSn n-FETs, from individual process modules to a complete device. High-k gate stacks and NiGeSn metallic contacts for source and drain are characterized in independent experiments. To study both direct and indirect bandgap semiconductors, a range of 0 at.% to 14.5 at.% Sn-content GeSn alloys are investigated. Special emphasis is placed on capacitance-voltage (C-V) characteristics and Schottky-barrier optimization. GeSn n-FET devices are presented including temperature dependent I-V characteristics. Finally, as an important step towards implementing GeSn in tunnel-FETs, negative differential resistance in Ge0.87Sn0.13 tunnel-diodes is demonstrated at cryogenic temperatures. The present work provides a base for further optimization of GeSn FETs and novel tunnel FET devices

Process modules for GeSn nanoelectronics with high Sn-contents

In this paper we present a systematic study of GeSn n-FETs. First, process modules such as high-k metal gate stacks and NiGeSn-metallic contacts for use as source/drain contacts are characterized and discussed. GeSn alloys of different Sn content allow the study of the capacitance-voltage (CV) and contact characteristics of both direct and indirect bandgap semiconductors. We then present GeSn n-FET devices we have fabricated. The device characterization includes temperature dependent IV characteristics. As important step towards GeSn for tunnel-FET Ge0.87Sn0.13 tunnel-diodes with negative differential resistance at reduced temperature are shown. The present work provides a base for further optimization of GeSn FET and novel tunnel FET devices

Correlation of bandgap reduction with inversion response in (Si)GeSn/high-k/metal stacks.

The bandgap tunability of (Si)GeSn group IV semiconductors opens a new era in Si-technology. Depending on the Si/Sn contents, direct and indirect bandgaps in the range of 0.4 eV to 0.8 eV can be obtained, offering a broad spectrum of both photonic and low power electronic applications. In this work, we systematically studied capacitance-voltage characteristics of high-k/metal gate stacks formed on GeSn and SiGeSn alloys with Sn-contents ranging from 0 to 14 at.% and Si-contents from 0 to 10 at.% particularly focusing on the minority carrier inversion response. A clear correlation between the Sn-induced shrinkage of the bandgap energy and enhanced minority carrier response was confirmed using temperature and frequency dependent capacitance voltage-measurements, in good agreement with k.p theory predictions and photoluminescence measurements of the analyzed epilayers as reported earlier. The enhanced minority generation rate for higher Sn-contents can be firmly linked to the bandgap reduction in the GeSn epilayer without significant influence of substrate/interface effects. It thus offers a unique possibility to analyze intrinsic defects in (Si)GeSn epilayers. The extracted dominant defect level for minority carrier inversion lies approximately 0.4 eV above the valence band edge in the studied Sn-content range (0 to12.5 at.%). This finding is of critical importance since it shows that the presence of Sn by itself does not impair the minority carrier lifetime. Therefore, the continuous improvement of (Si)GeSn material quality should yield longer non-radiative recombination times which are required for the fabrication of efficient light detectors and to obtain room temperature lasing action

(Si)GeSn nanostructures for light emitters

Energy-efficient integrated circuits for on-chip or chip-to-chip data transfer via photons could be tackled by monolithically grown group IV photonic devices. The major goal here is the realization of fully integrated group IV room temperature electrically driven lasers. An approach beyond the already demonstrated optically-pumped lasers would be the introduction of GeSn/(Si)Ge(Sn) heterostructures and exploitation of quantum mechanical effects by reducing the dimensionality, which affects the density of states. In this contribution we present epitaxial growth, processing and characterization of GeSn/(Si)Ge(Sn) heterostructures, ranging from GeSn/Ge multi quantum wells (MQWs) to GeSn quantum dots (QDs) embedded in a Ge matrix. Light emitting diodes (LEDs) were fabricated based on the MQW structure and structurally analyzed via TEM, XRD and RBS. Moreover, EL measurements were performed to investigate quantum confinement effects in the wells. The GeSn QDs were formed via Sn diffusion /segregation upon thermal annealing of GeSn single quantum wells (SQW) embedded in Ge layers. The evaluation of the experimental results is supported by band structure calculations of GeSn/(Si)Ge(Sn) heterostructures to investigate their applicability for photonic devices

GeSn lasers for CMOS integration

In search of a suitable CMOS compatible light source many routes and materials are under investigation. Si-based group IV (Si)GeSn alloys offer a tunable bandgap from indirect to direct, making them ideal candidates for on-chip photonics and nano-electronics. An overview of recent achievements in material growth and device developments will be given. Optically pumped waveguide and microdisk structures with different strain and various Sn concentrations provide direct evidence of gain in these alloys and the width of the emission wavelength range that can be covered. Towards the aim of electrically pumped lasers, a set of different homojunction light emitting diodes and more complex heterostructure SiGeSn/GeSn LEDs is presented. Detailed investigation of electroluminescence spectra indicate that GeSn/SiGeSn heterostructures will be advantageous for future laser fabrication

Low Temperature Deposition of High-k/Metal Gate Stacks on High-Sn Content (Si)GeSn-Alloys

(Si)GeSn is an emerging group IV alloy system offering new exciting properties, with great potential for low power electronics due to the fundamental direct band gap and prospects as high mobility material. In this Article, we present a systematic study of HfO2/TaN high-k/metal gate stacks on (Si)GeSn ternary alloys and low temperature processes for large scale integration of Sn based alloys. Our investigations indicate that SiGeSn ternaries show enhanced thermal stability compared to GeSn binaries, allowing the use of the existing Si technology. Despite the multielemental interface and large Sn content of up to 14 atom %, the HfO2/(Si)GeSn capacitors show small frequency dispersion and stretch-out. The formed TaN/HfO2/(Si)GeSn capacitors present a low leakage current of 2 × 10(-8) A/cm(2) at -1 V and a high breakdown field of ∼8 MV/cm. For large Sn content SiGeSn/GeSn direct band gap heterostructures, process temperatures below 350 °C are required for integration. We developed an atomic vapor deposition process for TaN metal gate on HfO2 high-k dielectric and validated it by resistivity as well as temperature and frequency dependent capacitance-voltage measurements of capacitors on SiGeSn and GeSn. The densities of interface traps are deduced to be in the low 10(12) cm(-2) eV(-1) range and do not depend on the Sn-concentration. The new processes developed here are compatible with (Si)GeSn integration in large scale applications

Direct bandgap GeSn microdisk lasers at 2.5 μm for monolithic integration on Si-platform

We report on the first experimental demonstration of direct bandgap group IV GeSn microdisk (MD) lasers (λem=2.5 μm) grown on Si(001). The evidence of lasing is supported by a detailed analysis of strain-dependent emission characteristics of GeSn alloys with xSn ≥ 12 at.%. Residual compressive strain within the layer is relieved via under-etching of the MD enabling increased energy offsets up to EL-EΓ=80 meV. The lasing threshold and max. temperature amount to 220 kW/cm2 and 135 K, respectively

GeSn lasers for monolithic integration on Si

Lasing under optical pumping is shown in suspended GeSn microdisks fabricated on a Ge virtual substrate with a lasing threshold below 1 mW at 20K

Direct bandgap GeSn alloys for laser application

Efforts towards development of monolithically integrated silicon-compatible lasers have been revitalized since the demonstration of optically pumped GeSn waveguide lasers. Here we investigate the laser emission of GeSn alloys by means of waveguide and microdisk photoluminescence