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Femtosecond-laser-driven photoelectron-gun for time-resolved cathodoluminescence measurement of GaN
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View: Figures


Image of FIG. 1.
FIG. 1.

Schematic representation of the TRPL and TRCL experimental setup for wide bandgap materials (after Ref. 19). The PE-gun is mounted on a home-made vacuum chamber. The Au photocathode is irradiated by a 3ω mode-locked Al2O3:Ti laser with rear-excitation configuration. The pressure of the chamber is approximately 10−4 Pa.

Image of FIG. 2.
FIG. 2.

The result of SIMION (Ref. 31) simulation of trajectories for the photoelectrons. The kinetic energy (E KE ) of electrons is set at 0.6 eV, from the relation between the excitation photon energy (4.43∼5.17 eV) and ϕ Au (4.3 eV). The given biases are V acc = –15 kV, V extract = 7.5 kV, V lens = 16 kV, and V OL = –8 kV. WD is a distance between the front edge of the PE-gun and the observation point.

Image of FIG. 3.
FIG. 3.

The photocurrent I PC (closed squares) and quantum efficiency η (closed circles) as a function of excitation photon energy. The excitation power density (per pulse) is approximately 2.5 μJ/cm2 for 270 nm, 1.3 μJ/cm2 for 260 nm, 1.4 μJ/cm2 for 250 nm, and 60 nJ/cm2 for 240 nm. The Au Faraday-cup was located at WD = 10 mm. The operating voltages were V acc = –10 kV and V extract = 6.0 kV.

Image of FIG. 4.
FIG. 4.

(a) I PC (closed circles) and e-beam diameter (D PC ) for WD = 10 mm (open triangles) and 52.5 mm (open squares) as a function of V acc . The V extract value was set at 7.5 ∼ 10 kV. (b) Representative I PC profile measured using the knife-edge method. In this case, the value of D PC is determined to be 30 μm, which is defined from the positions at 12 and 88% of the maximum.

Image of FIG. 5.
FIG. 5.

(a) PL spectra and (b) TRPL signals measured at 293 K of the Ga-polar AT-GaN and a GaN homoepitaxial film grown by MOVPE. The curve denoted by “system” represents the overall TRPL system response.

Image of FIG. 6.
FIG. 6.

(a) Room-temperature TRPL signals for the NBE emission peak of MOVPE homoepitaxial GaN film as a function of excitation power density, P. The TRCL signal is also shown (15 kV, 1.8 pA/cm2 per pulse). The curve denoted by “system” represents the overall system response for the TRPL system. (b) Effective PL / CL lifetimes (τ PL/CL, eff ) as a function of P.

Image of FIG. 7.
FIG. 7.

(a) The e-beam pulse length ℓ and (b) temporal e-beam broadening due to SCE (Δt SCE ) calculated as a function of propagation time. The electron number is N = 1, 10, 100, 300, 1500, and 10000. The measured system pulse width (FWHM) for the TRCL measurement is plotted by the closed circle (31 ps at t = 6 ns), which is limited by the streak-camera response.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Femtosecond-laser-driven photoelectron-gun for time-resolved cathodoluminescence measurement of GaN