Nanocrystallized Ge-Rich SiGe-HfO2 Highly Photosensitive in Short-Wave Infrared

Enhancing SiGeSn nanocrystals SWIR photosensing by high passivation in nanocrystalline HfO2 matrix

SiGeSn nanocrystals (NCs) in oxides are of considerable interest for photo-effect applications due to the fine-tuning of the optical bandgap by quantum confinement in NCs. We present a detailed study regarding the silicon germanium tin (SiGeSn) NCs embedded in a nanocrystalline hafnium oxide (HfO2) matrix fabricated by using magnetron co-sputtering deposition at room temperature and rapid thermal annealing (RTA). The NCs were formed at temperatures in the range of 500-800 °C. RTA was performed to obtain SiGeSn NCs with surfaces passivated by the embedding HfO2 matrix. The formation of NCs and β-Sn segregation were discussed in relation to the deposition and processing conditions by employing HRTEM, XRD and Raman spectroscopy studies. The spectral photosensitivity exhibited up to 2000 nm in short-wavelength infrared (SWIR) depending on the Sn composition was obtained. Comparing to similar results on GeSn NCs in SiO2 matrix, the addition of Si offers a better thermal stability of SiGeSn NCs, while the use of HfO2 matrix results in better passivation of NCs increasing the SWIR photosensitivity at room temperature. These results suggest that SiGeSn NCs embedded in an HfO2 matrix are a promising material for SWIR optoelectronic devices.

Crystallinity Effect on Electrical Properties of PEALD-HfO2 Thin Films Prepared by Different Substrate Temperatures

Hafnium oxide (HfO₂) thin film has remarkable physical and chemical properties, which makes it useful for a variety of applications. In this work, HfO₂ films were prepared on silicon through plasma enhanced atomic layer deposition (PEALD) at various substrate temperatures. The growth per cycle, structural, morphology and crystalline properties of HfO₂ films were measured by spectroscopic ellipsometer, grazing-incidence X-ray diffraction (GIXRD), X-ray reflectivity (XRR), field-emission scanning electron microscopy, atomic force microscopy and x-ray photoelectron spectroscopy. The substrate temperature dependent electrical properties of PEALD-HfO₂ films were obtained by capacitance-voltage and current-voltage measurements. GIXRD patterns and XRR investigations show that increasing the substrate temperature improved the crystallinity and density of HfO₂ films. The crystallinity of HfO₂ films has a major effect on electrical properties of the films. HfO₂ thin film deposited at 300 °C possesses the highest dielectric constant and breakdown electric field.

SiGeSn Quantum Dots in HfO2 for Floating Gate Memory Capacitors

Group IV quantum dots (QDs) in HfO2 are attractive for non-volatile memories (NVMs) due to complementary metal-oxide semiconductor (CMOS) compatibility. Besides the role of charge storage centers, SiGeSn QDs have the advantage of a low thermal budget for formation, because Sn presence decreases crystallization temperature, while Si ensures higher thermal stability. In this paper, we prepare MOS capacitors based on 3-layer stacks of gate HfO2/floating gate of SiGeSn QDs in HfO2/tunnel HfO2/p-Si obtained by magnetron sputtering deposition followed by rapid thermal annealing (RTA) for nanocrystallization. Crystalline structure, morphology, and composition studies by cross-section transmission electron microscopy and X-ray diffraction correlated with Raman spectroscopy and C–V measurements are carried out for understanding RTA temperature effects on charge storage behavior. 3-layer morphology and Sn content trends with RTA temperature are explained by the strongly temperature-dependent Sn segregation and diffusion processes. We show that the memory properties measured on Al/3-layer stack/p-Si/Al capacitors are controlled by SiGeSn-related trapping states (deep electronic levels) and low-ordering clusters for RTA at 325–450 °C, and by crystalline SiGeSn QDs for 520 and 530 °C RTA. Specific to the structures annealed at 520 and 530 °C is the formation of two kinds of crystalline SiGeSn QDs, i.e., QDs with low Sn content (2 at.%) that are positioned inside the floating gate, and QDs with high Sn content (up to 12.5 at.%) located at the interface of floating gate with adjacent HfO2 layers. The presence of Sn in the SiGe intermediate layer decreases the SiGe crystallization temperature and induces the easier crystallization of the diamond structure in comparison with 3-layer stacks with Ge-HfO2 intermediate layer. High frequency-independent memory windows of 3–4 V and stored electron densities of 1–2 × 1013 electrons/cm2 are achieved.