Crystal Phase Engineering in III-V Semiconductor Films: from Epitaxy to Devices

Philipp Staudinger
EPFL, 2020
Thèse EPFL

Résumé

Crystal phase engineering is an exciting pathway to enhance the properties of conventional semiconductors. Metastable SiGe presents a direct band gap well suited for optical devices whereas wurtzite (WZ) phosphide alloys enable efficient light emission in the green spectral range. Availability of these materials could profoundly impact electronics as well as solid-state lighting industries. However, their synthesis in high quality and beyond nanowire size constraints remained elusive, hampering both scientific and commercial exploitation.

In this thesis, we develop new approaches for metastable film growth to enable a platform for robust material characterization and device fabrication. Metal-organic vapor phase epitaxy is used to grow pure WZ nanowires and fins. To obtain planar layers, we explore two extensions of this well-known technique. The first one is based on conformal epitaxy and enables the use of standard (001)-oriented substrates. In this way, we achieve the controlled concurrent epitaxy of stable and metastable InP. We further propose a variation of this approach by using a nanowire as seed. This establishes a clear route for the synthesis of a large range of materials as is exemplarily demonstrated for WZ GaAs films.

For the second technique we explore a method to enforce epitaxial lateral overgrowth on (111)A-oriented substrates. This allows to deposit pure WZ InP layers on insulator exceeding areas of 100 µm2, the largest ever demonstrated. We conceive a nucleation-based model and argue on a fundamental size limitation of metastable film epitaxy.

Further advancement of this process allows to directly grow metastable micro- and nanostructures, which are optically isolated from the substrate. The high quality and shape-control of these crystals enables room-temperature lasing in WZ InP microdisks.

This thesis demonstrates the successful development of new concepts to synthesize metastable semiconductors with pure crystalline phase and dimensions tailored towards planar device fabrication. We expect our findings to significantly contribute to the realization of crystal phase engineered electronic and optoelectronic devices.

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https://infoscience.epfl.ch/record/278999?ln=fr

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Philipp Staudinger
EPFL, 2020
Thèse EPFL

Résumé

Official source

https://infoscience.epfl.ch/record/278999?ln=fr

À propos de ce résultat

Concepts associés (11)

Concepts associés

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Publications associées (1)

Publications associées

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Functional printing is a versatile mass production method that has gained considerable scientific and industrial attention in the past few years. A wide range of electronics from passive circuit components (e.g., resistors and interconnects) to high-performance transistors and high-quality displays can now be printed energy-, resource-, and cost-efficiently. In spite of the recent progresses in the formulation of inks and significant reductions in their production costs, most of the commercially available inks are still very expensive (e.g., silver inks), and limited to a few conductive and insulator materials that usually require high-temperature thermal treatments to become fully functional. To enable new applications, and further reduce the production costs, it is necessary to develop novel inks based on semiconductive and new conductive materials (with improved chemical or optical properties) that can become functional after drying (dry-only inks). Development of such inks is very challenging, and the few successful results have been mostly obtained by polymer-based inks, which suffer from cost and chemical-stability issues.Since 2004 and after the first successful isolation of single-layer pristine graphene, 2D materials have disrupted almost all fields of science and technology, from medicine, to electronics and beyond. Their unique morphology, diverse and widely-tunable physical and chemical properties, ease of synthesis, low-cost of production, and abundance of raw materials have brought up new possibilities, which were not conceivable before. Formulation of additive-free inks for room-temperature printing of electronics is one of such possibilities. In spite of their great potential, formulation of additive-free 2D-material-based inks has so far been limited to low-concentration inks that are not suitable for high-throughput manufacturing, which is one of the main incentives for printing of electronics. Furthermore, current 2D materials' synthesis and processing methods have either low yield, or are not scalable, which further limit their real-world applications. Here in this work, several processing and ink formulation strategies are reported, which can address the aforementioned problems and pave the way towards out of lab application of 2D materials.In chapter 1, after a brief introduction on different device fabrication methods, basics of liquid-phase processing, especially the topics that are related to ink formulation and printing, are concisely reviewed. In chapter 2, a universal strategy for additive-free formulation of pristine 2D materials-based inks, and their scalable production are reported. Being a universal approach, this method allows us to print advanced electronic devices consisting different types of semiconductive and conductive materials. MXenes are a recently discovered group of 2D materials with exceptional optical and electronic properties which can revolutionize the printed electronics industry. Due to their importance and being at their early stages of discovery, 2 chapters of this thesis (chapters 3 & 4) have been dedicated to their ink formulation challenges. In chapter 3, the possibility of using byproducts of MXene synthesis as a sustainable ink formulation strategy has been investigated, which can simultaneously address the financial and environmental issues of printing electronics. In chapter 4, the conventional MXene ink formulation strategies are revisited to enable their scalable printing.

EPFL2021

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EPFL2021