Takako Chinone

Subpicosecond exciton spin relaxation in GaN

The spin-relaxation process of A-band exciton in GaN is observed by spin-dependent pump and probe reflectance measurement with subpicosecond time resolution. The spin-relaxation times at 150−225K are 0.47−0.25ps. These are at least one order of magnitude shorter than those of the other III-V compound semiconductors. The spin-relaxation time τs is found to be proportional to T−1.4, where T is the temperature.

Picosecond spin relaxation of acceptor-bound exciton in wurtzite GaN

The spin relaxation process of acceptor-bound excitons in wurtzite GaN is observed by spin-dependent pump and probe reflectance measurement with subpicosecond time resolution. The time evolutions measured at 15–50K have a single exponential component corresponding to the electron spin relaxation time of 1.40–1.14ps. The spin relaxation time is found to be proportional to T−0.175, where T is the temperature. This weak temperature dependence indicates that the main spin relaxation mechanism is the Bir-Aronov-Pikus process [Sov. Phys. JETP 42, 705 (1976)].

Control of Emission Wavelength of GaInN Single Quantum Well, Light Emitting Diodes Grown by Metalorganic Chemical Vapor Deposition in a Split-Flow Reactor

We investigated the dependence of the electroluminescence (EL) characteristics on the layer thickness and the solid-phase composition of AlGaN clad layers in GaInN single-quantum-well light-emitting diodes (LEDs), and how to control the emission wavelength by the device structure. GaInN well layers were sandwiched by AlGaN clad layers, and GaInN inter layers were inserted between GaN n-contact and AlGaN n-clad layers. A wavelength shift of about 50 nm was achieved by changing either the Al solid-phase composition or the thickness of the clad layer. Due to an increase of the lattice mismatch between the clad and the well layers, the emission wavelength increased and the peak intensity decreased. Compared with the performance without an inter layer, the peak intensity increased 3.8 times. Moreover, by changing the growth temperature of the well layer, the LED wavelength can be varied from blue to red. Though the difference of the emission wavelength was 40 nm in the radial direction of the wafer, a luminous intensity of 1 cd for yellowish LEDs was achieved.

Picosecond spin relaxation of acceptor‐bound exciton in wurtzite GaN

The spin relaxation process of acceptor‐bound excitons in wurtzite GaN is observed by spin‐dependent pump and probe reflectance measurement with subpicosecond time resolution. The time evolutions measured at 15–50 K have a single exponential component corresponding to spin relaxation times of 1.40 – 1.14 ps. The spin relaxation time, τs, is found to be proportional to T−0.175, where T is the temperature. This temperature dependence is quite weak compared with that of A‐band free excitons showing τs ∝ T−1.41 at 150 – 225K.

Sub-picosecond exciton spin-relaxation in GaN

Exciton spin relaxations in bulk GaN were directly observed with sub-picoseconds time resolution. The obtained spin relaxation times of A-band free exciton are 0.47 ps - 0.25 ps at 150 K - 225 K. The spin relaxation time of the acceptor bound exciton at 15K is measured to be 1.1 ps. These are at least one order of magnitude shorter than those of the other III-V compound semiconductors. The spin relaxation time of A-band free exciton is found to be proportional to T -1.4, where T is the temperature. The fact that the spin relaxation time in GaN is shorter than that in GaAs, in spite of the small spin-orbit splitting, suggests that the spin relaxation is dominated by the defect-assisted Elliot-Yafet process.

Sub‐picosecond Spin Relaxation in GaN

The spin relaxation process of A‐band exciton in GaN is observed for the first time, to our knowledge, by spin dependent pump and probe reflectance measurement with sub‐picosecond’s time resolution. The spin relaxation times at 150–225 K are measured to be 0.47–0.25 ps. These are at least one order of magnitude shorter than those of the other III–V compound semiconductors. The spin relaxation time, τs, is found to be proportional to T−1.4, where T is the temperature.