Hoonill Jeong

Terahertz radiation from standing wave modes in GaN-based piezoelectric heterostructures

We report a newly found nano-acoustic motion of standing waves in an impedance-mismatched layer sandwiched by GaN-based piezoelectric heterostructures. The corresponding THz radiation features have been investigated in terms of the relevant layer thickness. If necessary, time-resolved photo-reflectance was performed to verify the spatial origins and to probe the decay dynamics of the standing waves within ~50 ps.

Electro-phononics for modulating acoustic pulses

The combined applications of vertical and lateral electric fields give rise to a novel degree of freedom in controlling transverse acoustic (TA) and longitudinal acoustic (LA) phonons. The coherent acoustic pulses were generated in GaN-based quantum wells (QWs) along polar c-axis under the ultrafast optical screening of the field-dependent strains and measured via the dynamic interference between reflected optical beams off the surface and the acoustic pulses. We electrically turned on the otherwise forbidden TA mode in the laterally biased region. The frequencies of the modes could be also modified via the field-induced changes in the propagation velocities. Finally, we experimentally investigated a novel method of controlling the phase of LA mode, generated from oppositely strained quantum wells and barriers under the vertical electric field.

Heat-spreading role of graphene studied by coherent phononic propagations

We have experimentally explored the role of graphene transferred on top of a GaN-based light-emitting diode (LED) as a heat spreading layer by monitoring the propagations of coherent acoustic phonons (CAPs).

Strain relaxation and quantum size effect studied by two-photon laser scanning photoluminescence microscopy

Nanoscale excitation by the simultaneous absorption of two photons was employed to investigate the spatially resolved role of strain relaxation and quantum size effect (QSE) in affecting luminescence from ZnO nanorods (NRs).

Electrically controllable detection of transverse acoustic phonons

In this work, we report on the electrical manipulation of photoelastic properties in wurtzite semiconductors for allowing transverse acoustic (TA) phonon detection.

Shadow excitation of nanoneedles: Roguing localization and strain effects from photoluminescence

In order to pinpoint the spatially resolved role of strain, localization, and quantum confinement (QC) in tapered nanoneedles (NNs), angle-resolved photoluminescence (PL) was adapted as a function of temperature.

Generation and frequency control of THz waves by nanoscale piezo-engineering

We report a newly found terahertz generation, mediated via acoustic standing waves confined within GaN-based piezoelectric heterostructures and its spectral control by adapting the active layer thickness.

Optical and THz characterization of p-In 0.64 Al 0.36 Sb for antenna application

Time-resolved photoreflectance was performed simultaneously with THz radiation measurements in a series of p-doped InAl0.36Sb. Carrier decay time can be as short as 350 fs depending on the doping density, which showed correlation with THz emission features.