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Young-Dahl Jho

Gwangju Institute of Science and Technology, Physics, Faculty Member

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Vladimir Jovanovic

Suvankar Chakraverty

Universidade de Brasília - UnB

University of Twente

M. Nadeem Akram

Christophe Coinon

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Papers by Young-Dahl Jho

Photoluminescence Signatures of Subband-specific Mobility Spectrum in Two-dimensional Electron gas System

New Physics: Sae Mulli, 2022

In this paper, we investigated a subband-specific relationship between electron mobility and phot... more In this paper, we investigated a subband-specific relationship between electron mobility and photoluminescence (PL) intensity in a modulation-doped In0.53Ga0.47As/In0.52Al0.48As heterostructure. From the steady-state diffusion model, the temperature-dependent mobility variation was anticipated to be inversely proportional to the PL intensity under lateral diffusion. The subband-mobility ratio fits best with the inverse ratio of the subband-specific PL intensity, especially in the high-temperature region (≥100 K), where the carrier mobility is less influenced by carrier localization using alloy disorder. Furthermore, the localization effects were manifested by an abrupt increase in PL decay time at the vicinity of electron de-trapping temperature, which coincides with abrupt changes in thermally stimulated capacitance.

Exceptionally slow rise in differential reflectivity spectra of excitons in GaN: Effect of excitation-induced dephasing

Physical Review B, 2003

Femtosecond differential reflectivity spectroscopy ͑DRS͒ and four-wave mixing ͑FWM͒ experiments w... more Femtosecond differential reflectivity spectroscopy ͑DRS͒ and four-wave mixing ͑FWM͒ experiments were performed simultaneously to study the initial temporal dynamics of the exciton line-shapes in GaN epilayers. Beats between the A-B excitons were found only for positive time delay in both DRS and FWM experiments. The rise time at negative time delay for the DRS was much slower than the FWM signal or differential transmission spectroscopy at the exciton resonance. A numerical solution of a six band semiconductor Bloch equation model including nonlinearities at the Hartree-Fock level shows that this slow rise in the DRS results from excitation induced dephasing, that is, the strong density dependence of the dephasing time which changes with the laser excitation energy.

Directional Terahertz Radiation from GaInP Lateral Superlattice

Journal of Nanoscience and Nanotechnology, 2015

We devised directionally controllable THz emission sources based on lateral composition modulatio... more We devised directionally controllable THz emission sources based on lateral composition modulation (LCM) structures. LCM structures were composed of In-rich Ga 0 47 In 0 53 P and Ga-rich Ga 0 51 In 0 49 P layers whose period was in quantum scale of ∼15 nm. The inherent type II band alignment in these structures leads to electron-hole (e-h) separation and plays a key role in generating laterally polarized dipole ensembles, thus concomitantly emitting enhanced transmissive THz waves as compared to bulk sample. On the other hand, in lateral geometry, changes in THz fields between LCM and bulk structures turned out to negligible since the vertical electronic diffusion was allowed in both samples.

Evidence for Superfluorescent Recombination from Dense Magneto-plasmas

Springer Series in Chemical Physics, 2000

We observe cooperative recombination (superfluorescence) from dense electronhole plasmas in Ino.2... more We observe cooperative recombination (superfluorescence) from dense electronhole plasmas in Ino.2Gao.8As multiple quantum wells pumped by intense femtosecond pulses in strong magnetic fields. At a critical fluence and magnetic field strength, superfluorescent bursts with unique characteristics are observed.

Directional Terahertz Radiation from GalnP Lateral Superlattice

Journal of nanoscience and nanotechnology, 2015

We devised directionally controllable THz emission sources based on lateral composition modulatio... more We devised directionally controllable THz emission sources based on lateral composition modulation (LCM) structures. LCM structures were composed of In-rich Ga0.47In0.53P and Ga-rich Ga0.51In0.49P layers whose period was in quantum scale of ~`5 nm. The inherent type II band alignment in these structures leads to electron-hole (e-h) separation and plays a key role in generating later- ally polarized dipole ensembles, thus concomitantly emitting enhanced transmissive THz waves as compared to bulk sample. On the other hand, in lateral geometry, changes in THz fields between LCM and bulk structures turned out to negligible since the vertical electronic diffusion was allowed in both samples.

Polarized Terahertz Waves Emitted from In0.2Ga0.8As Nanowires

Journal of nanoscience and nanotechnology, 2015

We investigate the polarizability of terahertz (THz) waves emitted from undoped In0.2Ga0.8As nano... more We investigate the polarizability of terahertz (THz) waves emitted from undoped In0.2Ga0.8As nanowires (NWs). THz emission amplitude shows strong enhancement in vertically aligned NWs compared to less-aligned NWs. In particular, polarized THz waves are clearly demonstrated in aligned NWs via a drastic variation of amplitudes as a function of the axis angle in polarization-sensitive photoconductive antenna. In addition, phase reversal between aligned and less-aligned NWs substantiates the geometrical dependence of electronic diffusion in generating the transient THz electric fields.

Nexus between coherent longitudinal-optical phonons and electronic diffusions in low-gap semiconductors

We have studied the characteristics of longitudinal-optical-phonon--plasmon coupled (LOPC) mode a... more We have studied the characteristics of longitudinal-optical-phonon--plasmon coupled (LOPC) mode as a function of thickness in InAs epilayers, ranging from 10 to 900 nm. The absence of LOPC modes in a scale less than exciton Bohr radius manifests the role of electron diffusion rather than the carrier screening via drift motion in surface depletion region.

Splitting of magneto-excitonic plasmas under intense femtosecond excitation in strong magnetic fields

Conference on Lasers and Electro-Optics/International Quantum Electronics Conference and Photonic Applications Systems Technologies, 2004

Novel magneto-exciton features are observed in InxGa 1-xAs quantum wells using intense femtosecon... more

Observation of Photoluminescence From Magneto-Plasmas Under Intense Femtosecond Excitation in Strong Magnetic Fields

High Magnetic Fields in Semiconductor Physics - Proceedings of the 16th International Conference, 2005

Anomalous magneto-plasmonic spectra: evidence for stimulated emission or superradiance?

2005 Quantum Electronics and Laser Science Conference, 2005

Novel magneto-plasmonic emission phenomena are observed from excited Landau levels in InxGa1-xAs ... more

Evidence for Ultrafast Superfluorescent Recombination from High-Density Magneto-Plasmas

15th International Conference on Ultrafast Phenomena, 2006

ABSTRACT Ultrafast cooperative recombination from dense electron-hole plasmas is observed in quan... more

Time-Resolved Carrier Dynamics in ZnO Epilayers and Nanorods

Frontiers in Optics, 2005

ABSTRACT We have measured the time-resolved differential reflectivity (TRDR) signal of ZnO epilay... more

<title>Ultrafast carrier relaxation and diffusion dynamics in ZnO</title>

Oxide-based Materials and Devices, 2010

We report on measurements and calculations of the ultrafast exciton relaxation dynamics in ZnO. T... more We report on measurements and calculations of the ultrafast exciton relaxation dynamics in ZnO. Time-resolved differential reflectivity measurements of bulk ZnO were performed as a function of excitation wavelength. Biexponential decays of the A and B exciton states are observed with a fast (∼2-5 ps scale) and a slower (∼50-100 ps scale) component, which depend strongly on excitation wavelength. Theoretical calculations based on a multi-state, coupled rate equation model were directly compared with the experiments to account for the rapid scattering between the A and B valence bands. Results show that the inter-valence band scattering is most likely not responsible for the fast initial relaxation. Instead our results show that carrier diffusion can play an important role in explaining the initial fast relaxation.

Generation and Frequency Control of THz Waves by Nanoscale Piezo-Engineering

Conference on Lasers and Electro-Optics 2010, 2010

We report a newly found terahertz generation, mediated via acoustic standing waves confined withi... more

Combined Effect of Carrier Localization and Polarity in In<SUB><I>x</I></SUB>Ga<SUB>1−<I>x</I></SUB>N/GaN Quantum Wells

Journal of Nanoscience and Nanotechnology, 2015

The influence of carrier localization and polarization-induced electric fields on the spectral va... more The influence of carrier localization and polarization-induced electric fields on the spectral variation of photoluminescence was comparatively studied in polar and semipolar InxGa1-x N/GaN strained quantum wells embedded in p-i-n diodes. Two representative structures with x = 0.16 for polar (0001) diodes and potential fluctuations for semipolar diodes grown along (1122) direction have been investigated with a reverse bias up to -4 V. From the s-shaped spectral shift as a function of temperature, the existence of single and triple localization traps was confirmed in polar and semipolar diodes. Within our bias range, we observed the monotonic blueshift with reverse bias in the polar sample, indicating that the carriers are laterally localized and thus influenced by the vertical piezoelectric fields. In clear contrast, the semipolar sample showed the blueshift of localized states only at low temperatures, while the deepest localization features were found at the highest available temperatures, overriding the influence of thermal activation and polarization fields.

Observation of Superfluorescence from Quantum Dots Created in Strong Magnetic Fields

Frontiers in Optics, 2005

ABSTRACT A novel cooperative emission phenomenon is observed in InxGa1-xAs quantum dots created b... more

Polarized Terahertz Waves Emitted from In<SUB>0.2</SUB>Ga<SUB>0.8</SUB>As Nanowires

Journal of Nanoscience and Nanotechnology, 2015

We investigate the polarizability of terahertz (THz) waves emitted from undoped In 0 2 Ga 0 8 As ... more We investigate the polarizability of terahertz (THz) waves emitted from undoped In 0 2 Ga 0 8 As nanowires (NWs). THz emission amplitude shows strong enhancement in vertically aligned NWs compared to less-aligned NWs. In particular, polarized THz waves are clearly demonstrated in aligned NWs via a drastic variation of amplitudes as a function of the axis angle in polarizationsensitive photoconductive antenna. In addition, phase reversal between aligned and less-aligned NWs substantiates the geometrical dependence of electronic diffusion in generating the transient THz electric fields.

Superfluorescence from magnetically formed quantum dots: mixing, temperature, and excitation pulsewidth dependence

2007 Conference on Lasers and Electro-Optics - Pacific Rim, 2007

ABSTRACT Ultrafast cooperative recombination from dense electron-hole plasmas in magnetically for... more

Superfluorescence from high-density magneto-plasmas: Mixing, temperature, and excitation pulsewidth dependence

2007 Quantum Electronics and Laser Science Conference, 2007

Ultrafast cooperative recombination from dense electron-hole plasmas in quantum wells is reported... more

Femtosecond coherent and incoherent spectroscopies on GaN

Technical Digest. CLEO/Pacific Rim '99. Pacific Rim Conference on Lasers and Electro-Optics (Cat. No.99TH8464), 1999

We have performed pump-probe (P-P) simultaneously with time-integrated-FWM as a function of the e... more We have performed pump-probe (P-P) simultaneously with time-integrated-FWM as a function of the energy of excitation and the excitation intensity. This shows that the tendency of the quantum beats, as revealed in the previous study, are the same both in P-P and FWM but the change of trace in the negative delays in P-P is markedly different from that in FWM. The P-P signals both at below-gap excitation and at the low intensity excitation show another oscillatory behavior distinct from the A-B exciton beats

Photoluminescence Signatures of Subband-specific Mobility Spectrum in Two-dimensional Electron gas System

New Physics: Sae Mulli, 2022

In this paper, we investigated a subband-specific relationship between electron mobility and phot... more In this paper, we investigated a subband-specific relationship between electron mobility and photoluminescence (PL) intensity in a modulation-doped In0.53Ga0.47As/In0.52Al0.48As heterostructure. From the steady-state diffusion model, the temperature-dependent mobility variation was anticipated to be inversely proportional to the PL intensity under lateral diffusion. The subband-mobility ratio fits best with the inverse ratio of the subband-specific PL intensity, especially in the high-temperature region (≥100 K), where the carrier mobility is less influenced by carrier localization using alloy disorder. Furthermore, the localization effects were manifested by an abrupt increase in PL decay time at the vicinity of electron de-trapping temperature, which coincides with abrupt changes in thermally stimulated capacitance.

Exceptionally slow rise in differential reflectivity spectra of excitons in GaN: Effect of excitation-induced dephasing

Physical Review B, 2003

Femtosecond differential reflectivity spectroscopy ͑DRS͒ and four-wave mixing ͑FWM͒ experiments w... more Femtosecond differential reflectivity spectroscopy ͑DRS͒ and four-wave mixing ͑FWM͒ experiments were performed simultaneously to study the initial temporal dynamics of the exciton line-shapes in GaN epilayers. Beats between the A-B excitons were found only for positive time delay in both DRS and FWM experiments. The rise time at negative time delay for the DRS was much slower than the FWM signal or differential transmission spectroscopy at the exciton resonance. A numerical solution of a six band semiconductor Bloch equation model including nonlinearities at the Hartree-Fock level shows that this slow rise in the DRS results from excitation induced dephasing, that is, the strong density dependence of the dephasing time which changes with the laser excitation energy.

Directional Terahertz Radiation from GaInP Lateral Superlattice

Journal of Nanoscience and Nanotechnology, 2015

We devised directionally controllable THz emission sources based on lateral composition modulatio... more We devised directionally controllable THz emission sources based on lateral composition modulation (LCM) structures. LCM structures were composed of In-rich Ga 0 47 In 0 53 P and Ga-rich Ga 0 51 In 0 49 P layers whose period was in quantum scale of ∼15 nm. The inherent type II band alignment in these structures leads to electron-hole (e-h) separation and plays a key role in generating laterally polarized dipole ensembles, thus concomitantly emitting enhanced transmissive THz waves as compared to bulk sample. On the other hand, in lateral geometry, changes in THz fields between LCM and bulk structures turned out to negligible since the vertical electronic diffusion was allowed in both samples.

Evidence for Superfluorescent Recombination from Dense Magneto-plasmas

Springer Series in Chemical Physics, 2000

We observe cooperative recombination (superfluorescence) from dense electronhole plasmas in Ino.2... more We observe cooperative recombination (superfluorescence) from dense electronhole plasmas in Ino.2Gao.8As multiple quantum wells pumped by intense femtosecond pulses in strong magnetic fields. At a critical fluence and magnetic field strength, superfluorescent bursts with unique characteristics are observed.

Directional Terahertz Radiation from GalnP Lateral Superlattice

Journal of nanoscience and nanotechnology, 2015

We devised directionally controllable THz emission sources based on lateral composition modulatio... more We devised directionally controllable THz emission sources based on lateral composition modulation (LCM) structures. LCM structures were composed of In-rich Ga0.47In0.53P and Ga-rich Ga0.51In0.49P layers whose period was in quantum scale of ~`5 nm. The inherent type II band alignment in these structures leads to electron-hole (e-h) separation and plays a key role in generating later- ally polarized dipole ensembles, thus concomitantly emitting enhanced transmissive THz waves as compared to bulk sample. On the other hand, in lateral geometry, changes in THz fields between LCM and bulk structures turned out to negligible since the vertical electronic diffusion was allowed in both samples.

Polarized Terahertz Waves Emitted from In0.2Ga0.8As Nanowires

Journal of nanoscience and nanotechnology, 2015

We investigate the polarizability of terahertz (THz) waves emitted from undoped In0.2Ga0.8As nano... more We investigate the polarizability of terahertz (THz) waves emitted from undoped In0.2Ga0.8As nanowires (NWs). THz emission amplitude shows strong enhancement in vertically aligned NWs compared to less-aligned NWs. In particular, polarized THz waves are clearly demonstrated in aligned NWs via a drastic variation of amplitudes as a function of the axis angle in polarization-sensitive photoconductive antenna. In addition, phase reversal between aligned and less-aligned NWs substantiates the geometrical dependence of electronic diffusion in generating the transient THz electric fields.

Nexus between coherent longitudinal-optical phonons and electronic diffusions in low-gap semiconductors

We have studied the characteristics of longitudinal-optical-phonon--plasmon coupled (LOPC) mode a... more We have studied the characteristics of longitudinal-optical-phonon--plasmon coupled (LOPC) mode as a function of thickness in InAs epilayers, ranging from 10 to 900 nm. The absence of LOPC modes in a scale less than exciton Bohr radius manifests the role of electron diffusion rather than the carrier screening via drift motion in surface depletion region.

Splitting of magneto-excitonic plasmas under intense femtosecond excitation in strong magnetic fields

Conference on Lasers and Electro-Optics/International Quantum Electronics Conference and Photonic Applications Systems Technologies, 2004

Novel magneto-exciton features are observed in InxGa 1-xAs quantum wells using intense femtosecon... more

Observation of Photoluminescence From Magneto-Plasmas Under Intense Femtosecond Excitation in Strong Magnetic Fields

High Magnetic Fields in Semiconductor Physics - Proceedings of the 16th International Conference, 2005

Anomalous magneto-plasmonic spectra: evidence for stimulated emission or superradiance?

2005 Quantum Electronics and Laser Science Conference, 2005

Novel magneto-plasmonic emission phenomena are observed from excited Landau levels in InxGa1-xAs ... more

Evidence for Ultrafast Superfluorescent Recombination from High-Density Magneto-Plasmas

15th International Conference on Ultrafast Phenomena, 2006

ABSTRACT Ultrafast cooperative recombination from dense electron-hole plasmas is observed in quan... more

Time-Resolved Carrier Dynamics in ZnO Epilayers and Nanorods

Frontiers in Optics, 2005

ABSTRACT We have measured the time-resolved differential reflectivity (TRDR) signal of ZnO epilay... more

<title>Ultrafast carrier relaxation and diffusion dynamics in ZnO</title>

Oxide-based Materials and Devices, 2010

We report on measurements and calculations of the ultrafast exciton relaxation dynamics in ZnO. T... more We report on measurements and calculations of the ultrafast exciton relaxation dynamics in ZnO. Time-resolved differential reflectivity measurements of bulk ZnO were performed as a function of excitation wavelength. Biexponential decays of the A and B exciton states are observed with a fast (∼2-5 ps scale) and a slower (∼50-100 ps scale) component, which depend strongly on excitation wavelength. Theoretical calculations based on a multi-state, coupled rate equation model were directly compared with the experiments to account for the rapid scattering between the A and B valence bands. Results show that the inter-valence band scattering is most likely not responsible for the fast initial relaxation. Instead our results show that carrier diffusion can play an important role in explaining the initial fast relaxation.

Generation and Frequency Control of THz Waves by Nanoscale Piezo-Engineering

Conference on Lasers and Electro-Optics 2010, 2010

We report a newly found terahertz generation, mediated via acoustic standing waves confined withi... more

Combined Effect of Carrier Localization and Polarity in In<SUB><I>x</I></SUB>Ga<SUB>1−<I>x</I></SUB>N/GaN Quantum Wells

Journal of Nanoscience and Nanotechnology, 2015

The influence of carrier localization and polarization-induced electric fields on the spectral va... more The influence of carrier localization and polarization-induced electric fields on the spectral variation of photoluminescence was comparatively studied in polar and semipolar InxGa1-x N/GaN strained quantum wells embedded in p-i-n diodes. Two representative structures with x = 0.16 for polar (0001) diodes and potential fluctuations for semipolar diodes grown along (1122) direction have been investigated with a reverse bias up to -4 V. From the s-shaped spectral shift as a function of temperature, the existence of single and triple localization traps was confirmed in polar and semipolar diodes. Within our bias range, we observed the monotonic blueshift with reverse bias in the polar sample, indicating that the carriers are laterally localized and thus influenced by the vertical piezoelectric fields. In clear contrast, the semipolar sample showed the blueshift of localized states only at low temperatures, while the deepest localization features were found at the highest available temperatures, overriding the influence of thermal activation and polarization fields.

Observation of Superfluorescence from Quantum Dots Created in Strong Magnetic Fields

Frontiers in Optics, 2005

ABSTRACT A novel cooperative emission phenomenon is observed in InxGa1-xAs quantum dots created b... more

Polarized Terahertz Waves Emitted from In<SUB>0.2</SUB>Ga<SUB>0.8</SUB>As Nanowires

Journal of Nanoscience and Nanotechnology, 2015

We investigate the polarizability of terahertz (THz) waves emitted from undoped In 0 2 Ga 0 8 As ... more We investigate the polarizability of terahertz (THz) waves emitted from undoped In 0 2 Ga 0 8 As nanowires (NWs). THz emission amplitude shows strong enhancement in vertically aligned NWs compared to less-aligned NWs. In particular, polarized THz waves are clearly demonstrated in aligned NWs via a drastic variation of amplitudes as a function of the axis angle in polarizationsensitive photoconductive antenna. In addition, phase reversal between aligned and less-aligned NWs substantiates the geometrical dependence of electronic diffusion in generating the transient THz electric fields.

Superfluorescence from magnetically formed quantum dots: mixing, temperature, and excitation pulsewidth dependence

2007 Conference on Lasers and Electro-Optics - Pacific Rim, 2007

ABSTRACT Ultrafast cooperative recombination from dense electron-hole plasmas in magnetically for... more

Superfluorescence from high-density magneto-plasmas: Mixing, temperature, and excitation pulsewidth dependence

2007 Quantum Electronics and Laser Science Conference, 2007

Ultrafast cooperative recombination from dense electron-hole plasmas in quantum wells is reported... more

Femtosecond coherent and incoherent spectroscopies on GaN

Technical Digest. CLEO/Pacific Rim '99. Pacific Rim Conference on Lasers and Electro-Optics (Cat. No.99TH8464), 1999

We have performed pump-probe (P-P) simultaneously with time-integrated-FWM as a function of the e... more We have performed pump-probe (P-P) simultaneously with time-integrated-FWM as a function of the energy of excitation and the excitation intensity. This shows that the tendency of the quantum beats, as revealed in the previous study, are the same both in P-P and FWM but the change of trace in the negative delays in P-P is markedly different from that in FWM. The P-P signals both at below-gap excitation and at the low intensity excitation show another oscillatory behavior distinct from the A-B exciton beats