arXiv subjects

Pei-Cheng Ku

Publications and source records attributed to Pei-Cheng Ku.

9 recordsLinked to original sources

arXiv2025

InGaN Nanopixel Arrays on Single Crystal GaN Substrate

Indium gallium nitride (InGaN) quantum well (QW) micro- and nanoscale light-emitting diodes (LEDs) are promising for next-generation ultrafast optical interconnects and augmented/virtual reality displays. However, scaling to nanoscale dimensions presents significant challenges, including enhanced nonradiative surface recombination, defect and/or dislocation-related emission degradation and nanoscale pixel contact formation. In this work, we demonstrate strain-engineered nanoscale blue LED pixels fabricated via top-down nanostructuring of an all-InGaN quantum well/barrier heterostructure grown by plasma-assisted molecular beam epitaxy (PAMBE) on significantly low dislocation-density single-crystal GaN substrates. Sidewall passivation using atomic layer deposition (ALD) of Al2O3 enables excellent diode behavior, including a high rectification ratio and extremely low reverse leakage. Monte Carlo analyses suggest almost 100% yield of completely dislocation-free active regions for 450 nm nanopixels. Electroluminescence measurements show bright blue emission with a peak external quantum efficiency (EQE) of 0.46%. Poisson Schrodinger simulations reveal partial strain relaxation in the QW, effectively mitigating the quantum confined Stark effect (QCSE). Additionally, finite-difference time-domain (FDTD) simulations confirm that the nanoscale geometry enhances light extraction efficiency by over 40% compared to planar designs, independent of substrate materials. These results establish a scalable pathway for dislocation free, high-brightness InGaN microLED arrays suitable for advanced display and photonic systems.

physics.app-ph↗

arXiv2024

Sim2Real in Reconstructive Spectroscopy: Deep Learning with Augmented Device-Informed Data Simulation

This work proposes a deep learning (DL)-based framework, namely Sim2Real, for spectral signal reconstruction in reconstructive spectroscopy, focusing on efficient data sampling and fast inference time. The work focuses on the challenge of reconstructing real-world spectral signals under the extreme setting where only device-informed simulated data are available for training. Such device-informed simulated data are much easier to collect than real-world data but exhibit large distribution shifts from their real-world counterparts. To leverage such simulated data effectively, a hierarchical data augmentation strategy is introduced to mitigate the adverse effects of this domain shift, and a corresponding neural network for the spectral signal reconstruction with our augmented data is designed. Experiments using a real dataset measured from our spectrometer device demonstrate that Sim2Real achieves significant speed-up during the inference while attaining on-par performance with the state-of-the-art optimization-based methods.

cs.LG↗

arXiv2017

Impact of carrier localization on recombination in InGaN quantum wells and the efficiency of nitride light-emitting diodes: insights from theory and numerical simulations

We examine the effect of carrier localization due to random alloy fluctuations on the radiative and Auger recombination rates in InGaN quantum wells as a function of alloy composition, crystal orientation, carrier density, and temperature. Our results show that alloy fluctuations reduce individual transition matrix elements by the separate localization of electrons and holes, but this effect is overcompensated by the additional transitions enabled by translational symmetry breaking and the resulting lack of momentum conservation. Hence, we find that localization increases both radiative and Auger recombination rates, but that Auger recombination rates increase by one order of magnitude more than radiative rates. Furthermore, we demonstrate that localization has an overall detrimental effect on the efficiency-droop and green-gap problems of InGaN LEDs.

cond-mat.mtrl-sci↗

arXiv2016

Site-controlled InGaN/GaN single-photon-emitting diode

We report single-photon emission from electrically driven site-controlled InGaN/GaN quantum dots, fabricated from a planar light-emitting diode structure containing a single InGaN quantum well using a top-down approach. The location, dimension, and height of each single-photon-emitting diode are controlled lithographically, providing great flexibility for chip-scale integration.

cond-mat.mes-hall↗

arXiv2016

Charge-Tunable Indium Gallium Nitride Quantum Dots

III-Nitride quantum dots have emerged as a new chip-scale system for quantum information science, which combines electrical and optical interfaces on a semiconductor chip that is compatible with non-cryogenic operating temperatures. Yet most work has been limited to optical excitations. To enable single-spin based quantum optical and quantum information research, we demonstrate here quantized charging in optically active, site-controlled III-Nitride quantum dots. Single-electron charging was confirmed by the voltage dependence of the energy, dipole moment, fine structures and polarization properties of the exciton states in the quantum dots. The fundamental energy structures of the quantum dots were identified, including neutral and charged excitons, fine structures of excitons, and A and B excitons. The results lay the ground for coherent control of single charges in III-Nitride QDs, opening a door to III-Nitride based spintronics and spin-qubit quantum information processing.

cond-mat.mes-hall↗

arXiv2014

Carrier dynamics in site- and structure-controlled InGaN/GaN quantum dots

We report on the carrier dynamics in InGaN/GaN disk-in-a-wire quantum dots with precisely controlled location and structural parameters, including diameter, thickness and material composition. We measured the time-integrated and time-resolved spectra and the second-order correlation function of the photoluminescence from quantum dots with diameters ranging from 19 nm to 33 nm at temperatures of 10 K to 120 K. The influence of the small fluctuations in structural parameters, most importantly the quantum dot thickness, on the optical properties are also investigated through statistical correlations among multiple optical properties of many individual quantum dots. We found that in a single dot the strain-induced polarization field and the strain relaxation at the sidewall form a potential barrier to protect the exciton from reaching the sidewall surface. However, the exciton can overcome this potential barrier and recombine nonradiatively at the surface through two mechanisms: tunnelling through the barrier quantum mechanically and hopping over the barrier by attaining sufficient thermal energy. The former (latter) mechanism is temperature insensitive (sensitive) and dominates nonradiaitve exciton decay at low (high) temperatures. We also found that despite the good uniformities in structural parameters, all optical properties still exhibit inhomogeneities from dot to dot. However, all these inhomogeneities can be modeled by simply varying the potential barrier height, which also explains the observed correlation curves among all optical properties. Finally, we found that the biexciton-to-exciton quantum efficiency ratio, which determines the probability of multi-photon emission, can be tuned by adjusting the potential barrier height and the temperature, suggesting a new way to achieve single photon emission at high temperatures.

cond-mat.mes-hall↗

arXiv2014

How much better are InGaN/GaN nanodisks than quantum wells - oscillator strength enhancement and changes in optical properties

We show over 100-fold enhancement of the exciton oscillator strength as the diameter of an InGaN nanodisk in a GaN nanopillar is reduced from a few micrometers to less than 40 nm, corresponding to the quantum dot limit. The enhancement results from significant strain relaxation in nanodisks less than 100 nm in diameter. Meanwhile, the radiative decay rate is only improved by 10 folds due to strong reduction of the local density of photon states in small nanodisks. Further increase in the radiative decay rate can be achieved by engineering the local density of photon states, such as adding a dielectric coating.

cond-mat.mes-hall↗

arXiv2013

Single Photon Emission from Site-Controlled InGaN/GaN Quantum Dots

Single photon emission was observed from site-controlled InGaN/GaN quantum dots. The single-photon nature of the emission was verified by the second-order correlation function up to 90 K, the highest temperature to date for site-controlled quantum dots. Micro-photoluminescence study on individual quantum dots showed linearly polarized single exciton emission with a lifetime of a few nanoseconds. The dimensions of these quantum dots were well controlled to the precision of state-of-the-art fabrication technologies, as reflected in the uniformity of their optical properties. The yield of optically active quantum dots was greater than 90%, among which 13%-25% exhibited single photon emission at 10 K.

physics.optics↗

arXiv2004

Inducing electron spin coherence in GaAs quantum well waveguides: Spin coherence without spin precession

Electron spin coherence is induced via light-hole transitions in a quantum well waveguide without either an external or internal DC magnetic field. In the absence of spin precession, the induced spin coherence is detected through effects of quantum interference in the spectral domain coherent nonlinear optical response. We interpret the experimental results qualitatively using a simple few-level model with only the optical transition selection rule as its basic ingredients.

cond-mat.mes-hall↗