MRI: Development of Molecular Beam Expitaxy Apparatus for Growth of Two Dimensional Electron Gas Systems with Mobility of 100,000,000 cm2/Vs

Princeton University, Princeton NJ

Investigators

Abstract

0923369 Pfeiffer Princeton University Technical Abstract: The goal of the project is to construct a new molecular beam epitaxy (MBE) machine specifically designed to produce semiconductor hetero-structures of unprecedented purity and quality. The structures will be designed to yield two-dimensional electron system (2DES) samples having free carrier mobilities in excess of 100,000,000 cm2/Vs at cryogenic temperatures. At the low level of chemical and structural impurities envisioned, the free 2D electrons will interact primarily with each other through the many-body Coulomb interaction. The availability of such samples will enable an unprecedented level of inquiry into a broad range of fundamental questions in many-body phenomena in condensed matter physics. In the past, as the quality of 2D hetero-structures has improved, new physics has been discovered, that has led to two Nobel Prizes. These high quality 2DES are also expected to be important for the next generation of technology. They are crucial, for example, in examining topological approaches in quantum computing. Carrier mobility is a direct indication of semiconductor crystalline quality. Recent experiments have revealed the current record 2D electron mobility of 36,000,000 cm2/Vs is likely limited by residual chemical impurities located within the GaAs conducting channel. These impurities can arise from multiple sources: vacuum out-gassing and breakdown of the furnace parts containing the molten elemental sources in the MBE machine, chemical impurities in the elemental sources themselves, and leaks or out-gassing of the MBE chamber and the substrate heating equipment. In the new machine, improved vacuum pumping and the introduction of a novel vacuum cryopump will substantially reduce the levels of critical impurities. Based on recent results and calculations, we predict the new machine will be able to grow samples with carrier mobilities in excess of 100,000,000 cm2/Vs. Layman?s Abstract: The goal of the proposed project is a new crystal growth machine specifically designed to produce semiconductor crystals of record quality and purity. In present day crystals the free conduction electrons scatter off fixed residual chemical impurities, or off the neighboring conduction electrons. With this new MBE (Molecular Beam Epitaxy) machine we expect to produce crystals with strongly reduced impurity levels, so that the dominant scattering that the free electrons suffer will almost exclusively be from other free electrons. The electrons will be able to easily move about without running into fixed impurities, thus leading to the record ?mobility? in the project title. Such samples will enable an unprecedented level of inquiry into a broad range of fundamental questions in condensed matter physics. In the past, as crystal purity levels have improved, new results were discovered which led to Physics Nobel Prizes in 1985, and 1998. Such near-perfect crystals are also important for long range technological applications ? such as new approaches to computing after the current shrinking of microchips according to ?Moore?s Law? becomes no longer feasible. The MBE machine to be constructed will have record quality of vacuum inside ? fewer impurity molecules will be inside to contaminate the growing semiconductor crystal than in any other crystal growth machine in the world. The work will take place at the Princeton Institute for the Science and Technology of Materials and the Department of Electrical Engineering at Princeton University. About 150 students and researchers across the US will directly benefit from this project.