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Integration of semiconductors for optical sensing and communication

Photoluminescence from MBE-grown PbSe thin films
Cathodoluminescence spectroscopy of dislocations affecting InAs quantum dot samples
We specialize in III-V and IV-VI semiconductors that emit and detect light in the near and mid-infrared (1-10 ┬Ám). Our research enables better materials for data transmission, sensing, manufacturing, and environmental monitoring. We make high-quality epitaxial thin films and spend much of our time understanding how imperfections in the crystalline structure such as dislocations and point defects impact their optical properties. This holds the key to monolithic or hybrid integration schemes for lasers and LEDs with silicon and germanium substrates for new hybrid circuits that combine photonics and conventional electronics.


Synthesis and defect characterization in semiconductors for quantum systems

HRSTEM image of PbSe-on-GaAs films prepared by MBE
Schematic of a delta-doped nitrogen in diamond
We are developing semiconductors such as diamond and PbSe for applications in quantum information sciences. We aim to understand and engineer point and extended defects such as substitutional nitrogen, boron, vacancies, and dislocations in diamond. We are synthesizing PbSe-SnSe thin films and nanowires by molecular beam epitaxy to harness their large spin orbit coupling and topologically non-trivial surface states. Both diamond and PbSe can benefit from advances in crystal growth, defect characterization, and heteroepitaxial integration, and we are performing fundamental growth studies with these materials to point the way to device quality materials. These efforts are in collaboration with the UC Santa Barbara Quantum Foundry.

Synthesis science of layered and low-dimensional p-block metal chalcogenide semiconductors

Heterogeneous integration of layered SnSe on GaAs using a PbSe interlayer
Coherent phase boundaries between 3D (rocksalt) PbSnSe and layered PbSnSe 
We are synthesizing epitaxial films of p-block metal chalcogenides such as SnSe, GeSe, and Sb2Se3 and integrating them with III-V and Si substrates. These materials host a variety of novel electronic, optical, and thermal responses, including phase-change behavior, that arise from their unique bonding motifs giving rise to sheet, ribbon, or amorphous crystal structures. We aim to harness these properties for devices for optoelectronics, with an emphasis on the role of defects.

Fundamentals of 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)
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. While dislocations are extensively studied in metals, we are especially interested in understanding how dislocation behave under nonequilibrium conditions of light, current, and other forms of carrier injection (such as in semiconductor laser devices) that are unique to semiconductors and insulators. 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.