Collaborative Research: SiGeSn-based heterostructures for intersubband photonic materials

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Non-technical description:The goal of this project is to study and develop a new semiconductor material system based upon alloys of silicon, germanium, and tin (SiGeSn). This activity builds upon the expertise of one of the team in developing SiGeSn materials for a variety of photonic devices in the near- and mid-infrared (such as lasers and photodetectors). Theoretical work has predicted that SiGeSn materials could be grown in alternating atomically sharp stacks with germanium (Ge) layers to make sets of quantum wells whose electronic energy levels can be engineered by design to give an optical response in an undeveloped part of the electromagnetic spectrum: the very long wavelength infrared and the terahertz. Furthermore, due to the fact that each of the constituent atoms of the material resides in the same column of the periodic table (Group IV), the vibrations of the crystal do not induce electric dipoles and hence will not interact much with light and electrons – a highly beneficial property. Fundamental studies are pursued to (a) grow the specific compositions of the SiGeSn material in layered stacks with atomically sharp interfaces, (b) characterize the fundamental electronic properties of such materials, and (c) show in a proof-of-concept demonstration that a far-infrared optical transition can be engineered according to our designs. If successful, this work lays the foundation for new far-infrared and terahertz lasers and photodetectors so as to fully exploit the electromagnetic spectrum. In addition to the involvement of graduate and undergraduate students, one principal investigator participates in a research projects course designed for the recruitment and retention of underrepresented minority first-year engineering students, and the other principal investigator recruits involved students from a local HBCU. This new semiconductor material system is highly compatible with mainstream silicon semiconductor technology, which will ease transition to industry and will advance future US semiconductor manufacturing interests. Technical description:The research goal of this project is to investigate lattice-matched Ge/SiGeSn heterostructure quantum wells as a new material system for n-type intersubband optoelectronic devices in the mid-infrared and far-infrared spectral range. The motivation lies in the fact that such group-IV semiconductors are non-polar, which results in a dramatically different character of the optical phonon interactions compared with III-V heterostructures widely used for intersubband devices. For example, (a) there is dramatically reduced intersubband electron-phonon nonradiative scattering and (b) drastic reduction of the strong absorption of light by optical phonons associated with the Reststrahlen band. If successfully developed, this material system could lead to terahertz quantum-cascade lasers that operate at room-temperature with low power consumption; high-sensitivity quantum-well infrared photodetectors in the far- and mid-infrared; the ability to newly reach the far-infrared wavelengths of 30-60 microns with group IV semiconductor devices not accessible with conventional III-V materials. The research comprises complementary efforts in materials growth and characterization, THz and far-infrared intersubband optical spectroscopy, and culminating in a proof-of-concept demonstration of intersubband based photoconductivity. Development of the SiGeSn material system for infrared and THz photonics opens the possibility of foundry-based growth of devices on 300-mm wafers, and integration with next generation integrated “silicon” photonic platforms in the mid-infrared. This has the potential to benefit many applications in sensing, thermal imaging, communications, and spectroscopy.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.