The advancement of next generation electronics requires breakthroughs in materials, functionalities and even device operation paradigms, in order to address challenges such as thermal management and charge tunneling as devices continue to be miniaturized. Graphene has recently generated a great deal of excitement as a one-atom thick conductor with exceptional electronic properties with especially high mobility electrons, with the 2010 Physics Nobel prize being awarded for groundbreaking work on this material. However, as graphene is not a semiconductor, digital electronics realizations such as those forming the basis of computing devices are difficult. Phosphorene, a single or few layers of black phosphorus, a stable layered phosphorus allotrope, has highly mobile electrons like graphene but is also a semiconductor like silicon. This potentially enables it to form the basis for digital electronics and logic gates. However, many of its basic properties are unknown and, since phosphorus reacts with air, device passivation is important. The proposed research aims to investigate device passivation, as well the fundamental properties of phosphorene, with the goal of realizing novel, high performance electronic and optoelectronic devices. The program will integrate the recruitment and education of undergraduate and graduate students, including those from under-represented groups, via semiconductor and materials research, and help to maintain the much-need pipeline of scientists and engineers for American technological sector. By outreaching to local high school students and teachers, this program will also positively impact the ethnically diverse local communities in Inland Empire.
The goal of this proposal is to investigate electronic, thermal and thermoelectric properties of mono- or few-layer black phosphorus, or phosphorene, and explore novel devices based on this new material. Phosphorene has emerged as a promising material for electronics and optical applications, due to its many desirable properties such as very high bulk mobility, in-plane anisotropy, expected large thermoelectric power and a direct band gap that is tunable by strain or thickness over a large range. However, basic properties such as the mobility bottleneck and major scattering mechanisms are not known and device passivation remains important. Our approaches include (1). fabrication of stable, high mobility devices by encapsulation, and optimization via control of substrate, protection layers, and Schottky barrier; (2). tuning device properties via ionic liquid gating and isotropic or anisotropic strain, (3). thermopower measurements of anisotropic Seebeck coefficients and Nernst power; (4). spatially modulated devices such as pn junctions for electronics, electroluminescence and photovoltaic applications, and twisted phosphorene bilayers for periodic band gap modulation. This program builds on the PI's and co-PI's strong track records on graphene and carbon nanotubes, and exciting preliminary data such as unprecedented mobility of 4000 cm2/Vs and observation of quantum oscillations in phosphorene. Outcomes of this research include elucidation of the fundamental material properties of single- and few-layer phosphorene, and providing the much-needed route for stable, high mobility devices, while exploration of anisotropic thermopower, pn junctions and twisted bilayers will open the door for novel electronic, thermoelectric and optoelectronic applications.
