Stanford
Semiconductor synthesis and defect science Mukherjee group, Materials Science and Engineering Mukherjee group, Materials Science and Engineering
Mukherjee group, Materials Science and Engineering

Research

The Mukherjee group specializes in semiconductors that emit and detect light in the infrared. Our research enables better materials for data transmission, sensing, manufacturing, and environmental monitoring. We make high-quality thin films and spend much of our time understanding how imperfections in the crystalline structure such as dislocations and point defects impact their electronic and optical properties. This holds the key to directly integrating these semiconductors with silicon and germanium substrates for new hybrid circuits that combine infrared photonics and conventional electronics.

Materials synthesis for near and mid-infrared optoelectronics

IV-VI materials
(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, also working closely with the UCSB Quantum Foundry.

 

Understanding dislocations and other extended crystal defects in semiconductors

Dislocations
(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 telecom lasers integrated with silicon technology, prepared via direct epitaxy (with the Bowers group at UCSB) and heterogeneously via wafer-bonding (with Intel) for growing needs in datacenters. 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 or thermal expansion mismatch between a film and the substrate and severely limit the performance of many devices such as transistors, lasers, and solar cells. We are using cutting-edge microanalysis and microscopy tools to understand the behavior of dislocations in semiconductors to understand how they impact laser performance. Understanding the properties of dislocations and controlling them is key to integrating the novel functionality of compound semiconductors with the scale of silicon technology.