Strain engineering of electrical and photovoltaic properties of 1D and 2D semiconductors
Doctoral thesis, 2024
Semiconductor nanowires and 2D-materials have unique physical properties that are suitable for various electronic and optoelectronic applications. The small physical dimensions, high surface-to-volume ratio and pristine crystallinity of the materials make them able to withstand high levels of elastic strain. Their elasticity makes these materials ideal candidates for elastic strain engineering (ESE), where strain is intentionally applied to enhance the desired physical properties of a material. Realization and investigation of ESE on nanomaterials require techniques that enable high resolution imaging and application and detection of strain on the nanoscale. In situ electron microscopy fulfills these requirements.
In this thesis work, in situ electron microscopy and Raman spectroscopy techniques were developed and applied to study ESE of charge transport and photovoltaic properties of individual GaAs nanowires and 2D MoS2. An in situ scanning tunneling microscope (STM) – focused ion beam and scanning electron microscope (FIBSEM) setup was developed to investigate ESE of individual GaAs nanowires. Furthermore, procedures to fabricate optimized electrical contacts on individual nanowires in the FIBSEM were established. Uniaxial tensile strain of more than 3% could be applied to the nanowires, which resulted in large modification of their current-voltage (I-V) characteristics, and an increased photocurrent by more than a factor of 4 during near-infrared illumination. The STM-FIBSEM setup was also used to transfer and study ESE of freestanding 2D MoS2 flakes. It was found that the applied strain modifies the I-V characteristics of 2D MoS2. Moreover, a piezo-straining device was developed to correlate electron microscopy, Raman spectroscopy and I-V characterization on the 2D-flakes. Evolution of strain distribution in 2D MoS2 due to applied stress was investigated by in situ Raman mapping.
In this thesis work, in situ electron microscopy and Raman spectroscopy techniques were developed and applied to study ESE of charge transport and photovoltaic properties of individual GaAs nanowires and 2D MoS2. An in situ scanning tunneling microscope (STM) – focused ion beam and scanning electron microscope (FIBSEM) setup was developed to investigate ESE of individual GaAs nanowires. Furthermore, procedures to fabricate optimized electrical contacts on individual nanowires in the FIBSEM were established. Uniaxial tensile strain of more than 3% could be applied to the nanowires, which resulted in large modification of their current-voltage (I-V) characteristics, and an increased photocurrent by more than a factor of 4 during near-infrared illumination. The STM-FIBSEM setup was also used to transfer and study ESE of freestanding 2D MoS2 flakes. It was found that the applied strain modifies the I-V characteristics of 2D MoS2. Moreover, a piezo-straining device was developed to correlate electron microscopy, Raman spectroscopy and I-V characterization on the 2D-flakes. Evolution of strain distribution in 2D MoS2 due to applied stress was investigated by in situ Raman mapping.
Semiconductor nanowires
Nanowire solar cells
2D semiconductors
GaAs nanowires
Elastic strain engineering
MoS2
Transition metal dichalcogenides
In situ electron microscopy
FB-salen, Origo, Kemigården 1, Chalmers
Opponent: Professor Andres Castellanos-Gomez, Materials Science Institute of Madrid, Spanish National Research Council, Spain.
Author
Jonatan Holmér
Nano and Biophysics DP
Enhancing the NIR Photocurrent in Single GaAs Nanowires with Radial p-i-n Junctions by Uniaxial Strain
Nano Letters,;Vol. 21(2021)p. 9038-9043
Journal article
Tuning Hole Mobility of Individual p-Doped GaAs Nanowires by Uniaxial Tensile Stress
Nano Letters,;Vol. 21(2021)p. 3894-3900
Journal article
An STM – SEM setup for characterizing photon and electron induced effects in single photovoltaic nanowires
Nano Energy,;Vol. 53(2018)p. 175-181
Journal article
Jonatan Holmér, Lunjie Zeng and Eva Olsson. Revealing mechanisms of ion beam milling to optimize electrical contacts on individual GaAs nanowires using analytical and in situ electron microscopy
Much of today’s technology is based on semiconductors. Semiconductors are a special type of material with unique electrical and optical properties. What makes semiconductors so useful is for example that they can absorb and emit light, and it is possible to regulate how well they conduct electricity by applying an electric field. These properties make semiconductors essential components in modern electronics, solar cells, LED lights, etc.
The further development of semiconductor technology relies on the continuous downscaling of the semiconductor material components to the nanometer and atomic scales, as well as enhancing the material properties through physical and chemical means. The latest developments in nanotechnology have made it possible to manufacture and manipulate semiconductor components at the nanometer scale. This not only enables miniaturization of devices but also unlocks completely new properties in the materials. An important characteristic of nanoscale semiconductors is that they are often much more elastic than their macroscopic counterparts. This provides us with additional mechanisms to tune the performance of semiconductor nanostructures using mechanical strain. By controlling the applied strain, the properties may be tailored and optimized for a specific application. This is a challenging task though, due to the small size of the components.
In this thesis, novel techniques for applying strain to nanomaterials have been developed. The techniques were used to investigate the impact of elastic strain in semiconductor nanowires and two dimensional semiconductor materials. The methodologies and insights provided by this work contributes to the understanding of how to utilize elastic strain to improve the functionality of semiconductor nanomaterials.
The further development of semiconductor technology relies on the continuous downscaling of the semiconductor material components to the nanometer and atomic scales, as well as enhancing the material properties through physical and chemical means. The latest developments in nanotechnology have made it possible to manufacture and manipulate semiconductor components at the nanometer scale. This not only enables miniaturization of devices but also unlocks completely new properties in the materials. An important characteristic of nanoscale semiconductors is that they are often much more elastic than their macroscopic counterparts. This provides us with additional mechanisms to tune the performance of semiconductor nanostructures using mechanical strain. By controlling the applied strain, the properties may be tailored and optimized for a specific application. This is a challenging task though, due to the small size of the components.
In this thesis, novel techniques for applying strain to nanomaterials have been developed. The techniques were used to investigate the impact of elastic strain in semiconductor nanowires and two dimensional semiconductor materials. The methodologies and insights provided by this work contributes to the understanding of how to utilize elastic strain to improve the functionality of semiconductor nanomaterials.
In Situ transmissionselektronmikroskopi studier av inverkan av mekanisk töjning hos halvledande nanotrådar
Swedish Research Council (VR) (2016-04618), 2017-01-01 -- 2020-12-31.
Areas of Advance
Nanoscience and Nanotechnology
Subject Categories
Physical Sciences
Nano Technology
Condensed Matter Physics
Infrastructure
Chalmers Materials Analysis Laboratory
ISBN
978-91-8103-126-3
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5584
Publisher
Chalmers
FB-salen, Origo, Kemigården 1, Chalmers
Opponent: Professor Andres Castellanos-Gomez, Materials Science Institute of Madrid, Spanish National Research Council, Spain.