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Research

Materials synthesis for near and mid-infrared optoelectronics

(a) The lattice-constant vs. band gap diagram showing the potential for creating heterostructures between IV-VI and III-V materials. (b) Cross-sectional TEM image showing epitaxial rocksalt PbSe on (001) oriented zincblende GaSb.

Epitaxial heterostructures of the rocksalt IV-VI semiconductors such as PbSnSe with zincblende III-V materials offer pathways to mid and far-infrared light emission and detection. Additionally, such semiconductors have a number of novel physical properties such as ferroelectricity, very large refractive indices, and also host topologically non-trivial states, making them a rich system to study. There are a number of crystal growth and material issues related to crystal structure and polarity mismatch that lead to crystal defects and carrier traps. We are performing fundamental growth studies with these dissimilar materials by molecular beam epitaxy to point the way to device quality materials.

Understanding dislocations and other extended crystal defects in semiconductors

 

(a) Segregation of foreign atoms at dislocations by pipe diffusion revealed by  atom probe tomography in InGaAs/Si. (b) In-situ observation of recombination-enhanced dislocation glide in (Al)GaAs/Si using electron channeling contrast imaging (ECCI, left) and cathodoluminescence spectroscopy (CL, right)

We have projects in reliability of quantum dot lasers on silicon (with the Bowers group at UCSB) and understanding how dislocations impact solar cell performance (with the Lee group at UIUC). We are using cutting-edge microanalysis and microscopy tools to understand the behavior of dislocations in semiconductors. Line defects in crystals known as dislocations are key to both the mechanical and electronic properties in semiconductors. They typically form due to lattice constant mismatch between a film and the substrate and severely limit the performance of many devices such as transitors, lasers, and solar cells. Understanding the properties of dislocations and controlling them is key to integrating the novel functionality of compound semiconductors with the scale of silicon technology.