Photodetection, single-photon devices, and III-nitride lasers
Physics-based simulation of optoelectronic devices operating in regimes where avalanche multiplication, high fields, quantum confinement, polarization, and electrothermal feedback matter.
Single-photon avalanche photodiodes
Achieving the photocurrent gain required for photon-flux-limited applications often requires avalanche photodiodes operated in Geiger mode. During a detection event, electron and hole populations can undergo stochastic impact ionization while the carrier distribution, electric field, and lattice temperature evolve together.
Carriers can gain several electron-volts between ionization events and populate high-lying bands and satellite valleys. Energy transferred to the lattice and screening by the growing carrier population can both suppress ionization, making Geiger-mode operation a nonlinear, non-equilibrium, coupled electrothermal problem.
The group has pioneered self-consistent electrothermal ensemble Monte Carlo approaches and studies device structure, bias, layer thickness, optical excitation, breakdown, and single-photon detection efficiency.
Optimization of III-nitride SPADs
Current work treats breakdown voltage and single-photon detection efficiency as consequences of the device design rather than fixed inputs. Composition, doping, electric-field profile, layer thickness, absorption, and stochastic avalanche probability can therefore be optimized together.
This provides a path from a physically faithful avalanche model to inverse device design: maximize useful detection probability while constraining field strength and other practical operating limits.
Recent III-nitride laser research
The group’s more recent laser work includes electro-opto-thermal design of III-nitride VCSELs, ultraviolet vertical-cavity laser design methodology, and AlGaN/InGaN ultraviolet multiple-quantum-well growth and stimulated emission. These studies connect device simulation directly to thermal management, epitaxial design, and experimentally realizable structures.
2019 VCSEL thermal-design paper · 2020 UV vertical-cavity laser-design paper · 2020 UV MQW growth/stimulated-emission paper
AlInGaN/InGaN blue and green lasers
Group III-nitride heterostructures enable short-wavelength and high-power optoelectronic devices, but accurate design requires coupled treatment of electronic structure, charge transport, polarization, recombination, and optical confinement.
The group's laser modeling work incorporates wurtzite material physics, Poisson and carrier-continuity equations, optical Helmholtz solutions, photon rate equations, thermionic transport, k·p bandstructure, many-body effects, and spontaneous and piezoelectric polarization.
Quasi-unipolar photodetection
The group proposed a high-speed photodetection concept in which unequal numbers of electrons and holes participate in the photocurrent, providing a design pathway to increased modulation bandwidth, improved optical saturation power, and reduced power dissipation.
