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 3x10(17) 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. (C) 2003 American Institute of Physics.

We propose and demonstrate a long-wavelength vertical cavity surface emitting laser (VCSEL) which consists of a (311)B InP-based active region and (100) GaAs-based distributed Bragg reflectors (DBRs), with an aim to control the in-plane polarization of output power. Crystal growth on (311)B InP substrates was performed under low-migration conditions to achieve good crystalline quality. The VCSEL was fabricated by wafer bonding, which enables us to combine different materials regardless of their lattice and orientation mismatch without degrading their quality. The VCSEL was polarized with a power extinction ratio of 31 dB. (C) 2003 American Institute of Physics.

We present stable polarization of a long-wavelength vertical-cavity surface-emitting laser (LW VCSEL). The polarization control was achieved through growing its active region on a (113)B InP substrate, which was integrated to (001) GaAs-based distributed Bragg reflectors by a wafer-bonding technique. Theoretical investigation showed that to achieve high polarization stability, a large dichroism such as an anisotropic gain is needed. It was also shown that the (113)B and other planes of the (11n) family have asymmetry, which results in asymmetric stress and anisotropic optical gain in a strained multiquantum well. An index-guiding mesa structure was fabricated in an asymmetric shape. The index guiding either enhanced or distracted the polarization stability originating from gain anisotropy, depending on its orientation of the asymmetry, as was confirmed by a statistical summary. Using a VCSEL with an appropriate index-guiding structure, we performed 1-Gb/s modulation and confirmed single polarization under large-signal modulation.

Traveling-wave photodetectors (TWPDs) are an attractive way to simultaneously maximize external quantum efficiency, electrical bandwidth, and maximum unsaturated output power. We review recent advances in TWPDs. Record high-peak output voltage together with ultrahigh-speed performance has been observed in low-temperature-grown GaAs (LTG-GaAs)-based metal-semiconductor-metal TWPDs at the wavelengths of 800 and 1300 nm. An approach to simultaneously obtain high bandwidth and high external efficiency is a traveling-wave amplifier-photodetector (TAP detector) that combines gain and absorption in either a sequential or simultaneous traveling-wave structure.