Electron relaxation and transport dynamics in low-temperature-grown GaAs under 1 eV optical excitation

Abstract

Electron relaxation and transport dynamics in low-temperature-grown GaAs under 1 eV optical excitation was investigated by femtosecond transient transmission measurement and electro-optical sampling measurement in bulk samples and fabricated devices. An increase in the electron lifetime can be observed when the electron density is higher than 3×1017 cm−3. This effect is attributed to prolonged electron relaxation due to intervalley scattering of highly excited electrons and associated hot phonon effects. Our conclusion is further supported by bias-dependent studies where intervalley scattering was achieved using high electric fields.

Device Saturation Behavior of Submillimeter-Wave Membrane Photonic Transmitters

“…The external light-THz conversion efficiency is a function of detector bias, optical excitation power, and antenna design. Under high bias voltage or high optical excitation, the conversion efficiency of the device saturates due to the carrier lifetime increasing effect in LTG-GaAs [8], [9]. The aim of this work is to find the optimum operation conditions of the device, such as applied bias voltage and excitation optical power, to maximize external conversion efficiency.…”

Traveling-Wave Photodetectors With High Power–Bandwidth and Gain–Bandwidth Product Performance

“…For 1230-nm subband-gap excitation, carriers in the mid-gap states can be excited into the valley with high excess energy ( 300 meV), which is close to the offset energy ( 310 meV) of the valley relative to the bottom. These photoexcited electrons will suffer from the intervalley scattering effect (Gunn effect) more easily as compared to the case of short wavelength excitation [30], [31]. This effect should reduce the electron capture rate back to the defect states and cause the broadening of the carrier-lifetime-limited device responses.…”

“…2 and 3, although the long wavelength MSM-TWPD has a much longer length, the maximum output is much lower than the case of short wavelength excitation. To understand the nonlinear behavior of LTG-GaAs-based PD under different wavelength excitations (800 versus 1230 nm), we have also performed EO sampling measurements in these two wavelength regimes with different pumping power [30], [31]. Also shown beside the traces are the corresponding collected carrier densities, which can be obtained by dividing the collected charges by the device absorption volumes.…”

“…We attributed this nonlinear behavior to the combination of different physical processes including carrier lifetime increasing [52], defect saturation, and space-charge screening effects [44], [45]. In the low optical excitation regime the dominant bandwidth limiting factor is carrier lifetime increasing and the FWHM increases with the bias voltage due to carrier heating and intervalley scattering [30], [31] instead of the reported coulomb-barrier lowering effect [52], because the electric field in the optical guiding mode center of our device is not high enough to induce this effect significantly [28], [30], [31]. When the photoexcited carrier density increases, the carrier trapping time will increase significantly because defect saturation reduces the carrier capture probability, and the drift time and significant space-charge field of photogenerated carriers start to affect the speed performance of the device.…”

“…By utilizing the short carrier trapping time of low-temperature-grown GaAs (LTG-GaAs) and the superior microwave guiding structure of metal-semiconductor-metal TWPD (MSM-TWPD) [27], record saturation power-bandwidth product performances of LTG-GaAs-based MSM-TWPD have been demonstrated in short ( 800 nm) [28] and long ( 1300 nm) telecommunication wavelengths regimes [29]. Distinct bandwidth degradation behavior, which can be attributed to hot electron effects of photogenerated carriers [30], [31], have also been observed. By utilizing the good speed and output power performances of MSM-TWPD, we have also demonstrated the novel structure of an LTG-GaAs-based terahertz photonic transmitter [32].…”