Research

Significant Research Developments and Contributions

2004-2023

Development of terahertz (THz) semiconductor quantum emitter and detector devices:

My group is currently the only research group in Canadian universities working on active terahertz quantum devices. I fabricated and demonstrated the first THz quantum cascade laser (QCL) in Canada in 2004 when I was on staff at the National Research Council. My early experimental study on the doping effect in THz quantum cascade lasers pinpointed the important balance between free carrier absorption loss and optical gain and discovered the optimum doping concentration, which has been widely adopted in the THz QCL research community. This work was cited more than 98 times according to Google Scholar. My continued research efforts explored the underlying physics of the quantum devices and made a few important discoveries, including direct measurement of the active-region temperature of lasing devices, direct observation of the thermal quenching of lasing operation, demonstration of a new approach to achieve electrically-controllable beam steering for THz QCLs, and demonstration of an intracavity terahertz time-domain spectroscopy experiment in terahertz quantum cascades lasers . In 2012, my group demonstrated record-breaking THz QCLs (highlighted by Nature Photonics March. 30th, 2012) in collaboration with NRC and MIT researchers, which is a significant milestone in the development of THz semiconductor quantum emitters. This paper has already been cited more than more than 600 times since 2012 according to Google Scholar. Moreover, my group proposed and demonstrated a new THz QCL structures based novel carrier injection and extraction scheme, which shows promising potential to bring THz QCLs’ performance to a new level. Inspired by this progress, my group continued to explore new quantum designs [Journal of Physics C 2015] and new device structure designs [Optics Express 2016] for improving device performance. More recently, the PI’s group proposed and demonstrated both theoretically and experimental a new THz QCL based on a novel quantum design – a hybrid extraction/injection design (HEID) that can effectively suppress thermally activated carrier leakage [Optics Express 2020]. The thermally activated carrier leakage is arguably the most important bottleneck in limiting THz QCL’s temperature performance. The proposed HEID scheme opens a promising approach to achieve room temperature lasing of THz QCLs – one of the long-desired research objectives in this field. My group also investigated a series of crucial underlying physics of device operation [Nanotechnology Reviews 2016, Optics Express 2018, Journal of Applied Physics 2021, Progress in Quantum Electronics 2021(Impact Factor (IF): 12.93)] . My group also successfully developed terahertz quantum well photodetectors, in which a novel doping profile was proposed to substantially enhance detector performance (detector sensitivity can be improved by one order of magnitude or more). The accumulated methodology, infrastructure and partnerships from the past research work have been facilitating a continual flow of new and novel concepts to move our research forward. In recognition of our expertise and research capabilities, two companies - one from Toronto (Alcohol Countermeasure Systems Corp.) and one from Florida, US (EMX international Inc.) - have separately invited my group to develop mid-infrared quantum cascade lasers for their prototype products.

2001-2015

Nanoscopic imaging of the beating heart of lasing quantum devices:

My group has developed and applied novel cryogenic-temperature scanning probe microscopy (SVM) to terahertz quantum cascade lasers and interband cascade lasers (ICLs). It is always very challenging to connect the internal microscopic physics with the external macroscopic performance in quantum photonic devices, particularly when the devices are in operating conditions. To address this challenge, the PI’s group successfully developed and applied novel cryogenic temperature scanning probe microscopy (SVM) to terahertz quantum cascade lasers and interband cascade lasers. For the first time, my group visualized directly, and quantitatively measured, the electric field domains (EFDs) in a lasing THz QCL, and identified the exact location of the EFD boundary [Scientific Reports 2014, IF: 5.13]. The results provided a clear-cut answer to a long-puzzling question in active semiconductor quantum photonic devices and represented a significant milestone in revealing the quantum dynamics in semiconductor quantum structures that hold many important applications. Using this novel metrology, the PI’s group quantitatively measured a few crucial physical parameters (electrical potential, electrical field, charge carriers) at nanometer scales in a lasing interband cascade laser (ICL) for the first time. The research results were published in Laser & Photonics Review (IF: 10.66).

2005-2014

Development of organic/inorganic hybrid optical upconversion devices:

My group proposed and demonstrated the first prototype hybrid organic/inorganic devices by direct tandem integration and studied the effects of interfacial states on device performance. The devices convert near-infrared light directly to visible light (green) at room temperature. A series of new-structure organic/inorganic optical upconverter were proposed and demonstrated and a record-high upconversion efficiency (~1.55W/W) was demonstrated. We also demonstrated the first-ever organic/inorganic optical upconversion pixelless imaging device in 2011. Two papers were published in Advanced Materials, which has an impact factor of 30.85. The research results pave the way for developing large-area, low-cost and high-efficiency near-infrared imaging devices, which can be used for night vision, manufacture quality control, biomedical imaging and other important applications. One US patent based on this technology was recently granted (US patent # 9,082,922), and two other patents are pending on decision.

2010-2023

Piezoelectric and triboelectric nanogenerators: an enabling green energy technology:

Piezoelectric and triboelectric nanogenerators can convert ubiquitously available mechanical energy to electrical energy, thus have profound applications in self-powered electronics, implantable biomedical devices, remote sensing, Internet of Things (IoTs), structure health monitoring and green energy techniques [IEEE Transactions on Nanotechnology 2018]. However, the low device efficiency and the lack of the flexibility of integrating nanogenerators on heterogeneous substrates have impeded the adoption of this technique. By taking advantage of nanomaterials and nanotechnology, My group successfully developed the first ZnO nanowire pn junction based nanogenerators [Journal of Applied Physics 2015]. The experimental results show that the devices’ piezoelectric performance can be enhanced by more than eleven-fold through properly controlling the doping concentration of the p-segment (lithium-doped) of the ZnO nanowires. My group also fabricated and demonstrated the first InN nanowire based nanogenerators [Nanoscale, 2016 Impact Factor (IF): 7.79]. My group proposed and demonstrated a compact hybrid energy cell (CHEC) through the integration of a piezoelectric nanogenerator with a silicon-based solar cell, which can simultaneously harvest optical and mechanical energy and convert to electrical energy to power wireless strain sensors or light emitting diodes. This research work was published in a highly-prestigious journal [Nano Energy 2016, IF: 17.88]. By employing more new nanomaterials, the PI’s group has developed a series of novel nanogenerator devices, including a consolidated device based on 1D/2D hybrid zinc oxide nanostructures [Advanced Materials Interfaces 2018, IF: 6.14], a hybrid nanogenerator with mutual performance enhancement [Nano Energy 2019, IF: 17.88] and a high performance piezoelectric nanogenerator based on organic/inorganic nanomaterials with porosity [ACS Applied Materials & Interfaces 2020, IF: 9.22]. The relevant research progress led to a breakthrough – the development of a self-powered multi-broadcasting wireless sensing system that was based on an all-in-one triboelectric nanogenerator [Nano Energy 2019, IF: 17.88]. A series of patents have been filed to protect the intellectual properties of the research results.

2018-2023

Exploiting perovskite materials for new functions:

As one of the most abundant structural families, perovskites are found in an enormous number of compounds which have wide-ranging properties and applications. The main device applications of perovskite have been focused on the fabrication of photovoltaics, lasers, light-emitting diodes and scintillators. By taking advantage of the superior piezoelectric properties of perovskites, the PI’s group developed self-assembled highly-ordered porous perovskite/PVDF composite films for harvesting mechanical energy [Journal of Materials Chemistry A, 2020, IF: 11.3]. More recently, my group achieved ultrahigh piezoelectricity in organic-inorganic vacancy-ordered halide double perovskites [ACS Energy Letters 2021, IF: 19.05] and demonstrated superior transverse piezoelectricity in organic-inorganic hybrid perovskite nano-rods [Nano Energy 2021, IF: 17.88]. Novel materials and their new applications have been explored and demonstrated by my group and collaborators [Solar RRL 2021, IF: 8.58; ACS Applied Materials & Interfaces 2021, IF: 9.22; Nanoscale 2021, IF: 7.79; Journal of the American Chemical Society (JACS) 2020, IF: 15.42; Joule 2020, IF: 24.67; Nature Communications 2023, IF: 17.69].

Sponsors

  • NSERC
  • CFI
  • ORF
  • University of Waterloo
  • OCE
  • NRC
  • CMC
  • Teledyn-DALSA
  • ACS Inc.
  • TeTechs
  • Chipworks
  • VueReal
  • Shimco
  • Norcada
  • AIH

Research Projects

  • Terahertz and mid-infrared quantum cascade lasers, design, fabrication, characterization and applications
  • Nanomaterial based energetic harvesting technology
  • Perovskite materials and devices
  • micro-LEDs and micro-photodetectors
  • Terahertz and mid-infrared quantum well photodetector
  • Nanofabrication and Nanotechnology
  • Organic/inorganic hybrid optical upconversion, infrared imaging, biophotonics
  • Scanning probe microscopy, scanning voltage microscopy, scanning spreading resistance microscopy, scanning differential spreading resistance microscopy