Our research activities—from theoretical analysis, to fundamental research, to material and device development—have a broader impact on energy and sustainability, typically by enabling new types of future devices that require less energy to operate, or that are used for energy production or storage.
Many of our activities are part of SEEDS (Sustainable Semiconductor Exploration for Energy Devices and Systems), our interdisciplinary research and development initiative. SEEDS aims to drive innovation in semiconductor materials, devices, and systems, which are pivotal to the advancement of modern technology. These materials serve as the foundation for critical applications like computational engines, photovoltaic systems, high-efficiency lighting, optical and RF communications. Recognizing the evolving landscape, including the rise of quantum and neuromorphic computing, we anticipate a paradigm shift that necessitates the exploration of novel semiconductor materials and their integration into cutting-edge devices and systems.
Ultra-wide bandgap semiconductor single crystals
Renewable energy sources typically provide electrical energy sources which require conversion to be transported large distances and converted again to be used in a system. Performing this act efficiently is critical to reduce lost energy. Ultra-wide band gap semiconductors are materials that have the potential to make significant gains in this field given their materials properties and ability to operate at extreme voltages and conditions. In the department of materials science and engineering, the group of Prof. Siddha Pimputkar, is working on the synthesis of single crystals of ultra-wide bandgap materials in both bulk (substrates) and thin film format (device layers) to enable next-generation power electronic devices using Smith’s Lab at Lehigh.
In addition, the group is also working on the synthesis methods needed to grow, in bulk form, earth-abundant nitride materials, such as compounds using Zn,Si/Se/Mg, and N. These materials could be suitable for substrates for traditional III-N semiconductor devices. Earth-abundant nitride materials are of considerable interest because their availability would have a significant impact on reducing the need to extract elements from remote regions in the world with the ensuing geopolitical ramifications.
The importance of point defects
Point defects in semiconductors and other materials are responsible for a number of extraoridinary properties and can be a required addition to achieve required functionalities. The group of Prof. Michael Stavola in the department of physics is using detailed infrared spectrosocopy to discover and characterize such defects in semidonductors ranging from silicon to the current batch of ultrawide bandgap semiconductors that are attracting attention for application in next generation high-power devices and optoelectronic device the ultraviolet spectral range. As an example, the group found that in a wide bandgap semiconductor like Ga2O3 the unintentional presence of hydrogen impurities strongly impacts the observed conductivity. Fundamental studies of these hydrogen defects and their interactions with other defects in Ga2O3 provide a foundation for controlling conductivity, a key aspect towards the reliable engineering of device materials.
Ultrawide bandgap semiconductors like Ga2O3 are attracting much attention for application in next,generation, high-power and deep UV devices. Hydrogen impurities that are unintentionally present in Ga2O3 can strongly impact conductivity. Fundamenta. studies of H and its interactions with other defects in Ga2O3 provide a foundation for controlling conductivity so that device materials can be reliably engineered.
Electronics and Optoelectronics
The development of ultra-wide bandgap semiconductors, like the III-Nitrides mentioned above, is important towards superior optoelectronic and electronic devices in fields such as power electronics used in the electrical grid, and also towards new classes of more light emitters.
Several other fundamental investigations have relevance for solar energy harvesting with new materials such as lightweight organic systems, or for energy storage and new types of batteries. As an example, research pursued by the Reichmanis group focuses on active materials for lithium-ion electrodes that can have up to 10 times the charge capacity of the graphite electrodes used in current systems, like high-capacity magnetite and silicon anodes, while also exploring flexible electrodes and polymer electrolytes.
Fundamental investigations on excitons in organic materials contribute to progress in the area of solar energy harvesting through organic systems that may have a shorter lifetime or slightly lower efficiency, but would compensate for this by environmentally cheap to produce, by being lightweight, but the ability the ability of rolling out large sheets of energy-collecting plastic. The Biaggio group is investigating how photon absorption in molecular organic semiconductors can lead to two long-lived triplet excitons that are then easier to convert into photovoltaic current.
Even for photovoltaics systems based on conventional materials, like silicon, it is possible to lower the energy and cost required to manufacture them by controlling interfaces and directing electron flow. One way to do that is studied in the research group of Nick Strandwitz, and it consists of using atomic layer-deposited (ALD) tunnel barriers, which are so thin that electrons can tunnel through them, and can lead to silicon photovoltaic cells made with a combination of ALD tunnel barriers and metal oxides that selectively transport electrons with specific energies.
Circuits and devices with lower energy impact
The total annual energy consumption for computing is close to ~1% of world energy production, and is increasing at exponential speed. According to its current increasing speed, the computing energy consumption will be equal to the world’s total energy production by 2040. This growth is clearly unsustainable. The research in Prof. Ning Li’s group in the deprtement of electrical and computing enigneering aims at contributing to a dramatic reduction of the computing energy by finding greener materials and devices that create semiconductor chips and packages with radically improved energy efficiency, driving a revolution in the efficiency of future information and computing technology systems at scale. In particular, Li’s group is aiming at the discovery of new computing paradigms with a radically improved energy efficiency by focusing on 1) non-volatile memory devices for in-memory computing to increase the energy efficiency for AI work loads; 2) logic devices that further improves the conventional computing efficiency; and 3) optoelectronic devices and systems for optical interconnect for improved communication efficiency for moving data between chips and computing units.
Reliable rechargeable batteries with high energy density are critically needed for applications including consumer electronics, energy storage grids and electric vehicles, among others. Serving as one example, flexible batteries are considered as a promising approach for the creation of practical, aesthetic electronic devices owing to their potential to adapt to mechanical stress and thereby shape transformation. In that regard, considerable efforts have been aimed at developing robust flexible lithium-ion batteries based on incorporating sustainable, advanced materials and constructing new flexible, systematic platforms, including adoption of soft materials such as polymer electrolytes, nano-sized active materials, and highly patterned, flexible current collectors.
To accelerate the development of robust flexible batteries, the research group of Elsa Reichmanis in the department of chemical and biomolecular engineering is investigating the interfacial chemical properties at three key interfaces of high-capacity composite battery electrodes. Through elucidation of the complex molecular to mesoscale interactions between electrode components, the group can begin to develop the requisite fundamental chemical-structural relationships required for robust, next generation battery platforms.
Low cost quantum-dot light-emitting diodes for display applications
Prof. Reichmanis’ group is exploring the use of processing approaches such as blade coating to realize uniform solution processed layers required for colloidal quantum-dot light-emitting diodes (QLEDs). These devics offer opportunities for low-cost, less energy intensive, large area solution processing including traditional QLED advantages such as high brightness, solution processability, color tunability, and narrow emission bandwidth. For multicolor displays, printing and patterning of QDs require high resolution, throughput, and uniformity. The research will explore the relevant structure-property-performance relationships. Photophysical studies will provide new physical insights into this class of materials, which offers opportunities for low-cost, less energy intensive, large area solution processing including traditional QLED advantages such as high brightness, solution processability, color tunability, and narrow emission bandwidth.
Developments in optics and photonics have already contributed to an enormous amount of energy savings by allowing to transmit information via photons in optical fibers instead of using expensive to produce and operate copper cables. In addition, the future possibility of using photons for data processing will also contribute to energy savings. This ranges from the development of all-optical switches in which optical waves can perform operations on bits transported by other optical waves, to the ability to quickly move information from the electronic to the optical domain, where it can be transmitted without losses in fibers and optical waveguides, a technology that promises to save a lot of energy in data centers when connecting the multiple cores of computer clusters.
Organic material for integrated photonics can provide active functionality for either ultrafast all-optical switching or ultrafast electro-optic modulation in advanced integrated optics circuitry. This can enable more efficient components and devices, with the large energy savings that are important for sustainability, in particular inside the computers and networks found in large computing facilities and large data centers. Examples are the use of optical circuits on the silicon photonics platform in tandem with nanoelectronic and microelectronic circuits to manage data transmission and data processing in computer networks, where copper connections would be replaced by fiber optics and bits of data need to be created and processed optically.
Work on using small organic molecules to add active photonics functionality to passive integrated optics circuits such as the silicon photonics platform is being done in Biaggio’s group, in the context of exploring the appeal of small molecules for practical nonlinear optics. The group has demonstrated new, small-molecule based organic glasses that can be used for all-optical switching on the silicon-photonics platform thanks to their large third-order noninear optial susceptibility coupled with easy processing and fabrication using physical vapor deposition. Another recent area of research focuses on developing a flexible way to systematically and reproducibly add electro-optic modulation functionality to passive integrated optical circuit elements, which can be done by depositing an organic molecular glass that is then electrically poled. Such systems would help enable an ultrafast transfer of data from the electrical to the optical domain, which can cut down on the energy consumed in data centers where data is sent back and forth between different processors using copper cable, requiring active cooling.
Conjugated polymers offer opportunities for the development of low-cost, flexible and stretchable, energy efficient devices for applications ranging from organic photovoltaics, organic field effect transistors, organic light emitting diodes, and biomedical sensors. The group of Prof. Elsa Reichmanis in the department of chemical and biomolecular engineering works on the design, synthesis, and development of organic and hybrid semiconductor materials and processes. To take full advantage of organic semiconductor technology, solution processed materials are required for conventional mass printing applications. The development of viable active polymer materials for such applications requires not only the development of relevant chemistries, but also the development of compatible device fabrication processes. The group is developing energy efficient processing techniques to manipulate and control the micro-/macro-structure of thin conjugated polymer films and investigating how the resultant structure impacts macroscopic charge transport within the material. Techniques such as absorption and vibrational spectroscopy, atomic force microscopy, x-ray diffraction and electrical measurements of thin films are employed to understand relationships between molecular structure, thin film architecture, optical properties and macroscopic charge transport in organic/polymer/hybrid semiconductor materials. Features extracted from microstructural data are analyzed through image analysis, peak fitting, and other techniques from the rapidly growing field of data science. Efforts to elucidate the role of interfaces are also in progress
Characterization of photoactive materials for solar energy
Photoactive materials represent an active and ongoing area of interest to the scientific community due to their relevance in many applications including photocatalysis, photosensing, photovoltaics, light-emitting diodes, photodetectors, and field effect transistors. The research group of Prof. Elizabeth Young in the department of chemistry is conducting research that will need to a better understanding of how charges flow and how material interfaces mediate charge transfer across multiple layers in relevant photophysical mechanisms. As an example, the group is using transient absorption spectrsocopy on a completed transparent Sb2S3-based solar cell. Doing so, they observed the first demonstration that inclusion of a top transparent contact on a Sb2S3 solar cell changes the behavior and lifetimes of charge carriers, and hence the photophysical mechanism. The ability to characterize in this wayreal-life solar cell devices is essential in order to vetter understand the dynamics at play and drive their continued development..
Fundamental studies of exciton dynamics in organic semiconductors
The research group of prof. Ivan Biaggio in the department of physics is studying the fundamental physics involved in multi-exciton generation and the charge transport processes that determine the functionality of future solar energy harvesting systems that include organic materials, from hybrid organic-silicon system to fully “plastic” solar cells that could be produced as very large, light, and cheap sheets that would provide an important flexible addition to existing technology, even for moderate efficiencies.
One important research direction is the use of such investigative techniques as pump and probe experiments with tunable excitation, and time-correlated single photon counting, to study singlet-triplet exciton conversion, transport, and dissociation in organic single crystal semiconductors. This includes the investigation of the fundamental mechanisms of singlet exciton fission into a pair of triplet excitons quasiparticles that are in an entangled quantum state and maintain such enanglement as they diffuse inside the crystal lattice.
Rare earth doped materials in quantum information science and engineering
Next generation secure communication networks and computing will rely on systems that take advantage of the quantum nature of the carriers of information and the objects calculations are carried out with. In this it is essential to prepare, manipulate, and read out the quantum states of these objects. Doping rare earth ions with their characteristic 4f shell of their valence electrons and their magnetic properties is a promising approach to implement quantum functionality in solid state materials.
In semiconductors like GaN and GaAs rare earth ions can be excited electrically with high efficiency enabling e.g.: highly efficient red LEDs that can be integrated with standard very mature GaN technology. Prof. Volkmar Dierolf in the department of phyiscs, and his collaborators, are exploring the possibility of building a single photon emitter, a key element for secure quantum communications, using these materials. In another project, the group is working with the Himanshu Jain’s group to develop the ability to control the growth of high quality single crytals in glass using localized laser heating. These crystals can be integrated into photonic circuits, provide functionality such as light modulation and polarization control, and they can act as a high quality host for doping with rare earth ions making them promising systems to realize quantum memories and quantum repeaters that are embedded with small losses within optical quantum network