No abstract

No abstract

Gas source molecular beam epitaxal growth of GaSb is investigated. Sb(CH3)3 is found to decompose effectively when the cracking furnace temperature is higher than 800°C. A mirror-like GaSb epi-layer is shown to be obtainable using Sb(CH3)3 and a solid Ga source for the first time.

Device design for unitraveling-carrier photodiodes (UTC-PDs) and their derivative structures is reconsidered from the point of view of terahertz (THz) applications. A key design procedure for maximizing their bandwidth is optimization by incorporating hybrid absorbers. The effect of quasi-field in p-type absorber is carefully examined. It has been shown that the initial velocity transient must be taken into account to evaluate the effective average velocity. Photomixers integrating a hybrid-absorber UTC-PD and a bow-tie antenna were fabricated and characterized. THz-wave generation by the photomixers in a frequency range of up to around 2.5 THz was confirmed. The observed THz-wave output exhibits significant changes with bias voltage, where the decrease in the output with increasing negative bias voltage is more pronounced at higher frequencies. This output behavior is due to the change in electron velocity in the diode depletion layer associated with the overshoot effect. From the dependence of the output power on frequency, effective electron velocity is found to be as high as 6 × 10 7 cm/s at optimum bias voltage of −0.4 V. Index Terms-Photodiode (PD), uni-traveling-carrier photodiode (UTC-PD), transient electron velocity, velocity overshoot, terahertz (THz), photomixer, antenna integrated photomixer.1077-260X

Photonic generation of continuous millimetre-and sub-millimetre waves up to the THz range using antenna-integrated uni-travelling-carrier photodiodes is described. A device integrating a wideband log-periodic antenna exhibits a maximum output power of 2.6 µW at 1.04 THz with good linearity. A module with a quasi-optical output port fabricated for practical use generates almost the same output power as the chip at around 1 THz and operates at frequencies of up to 1.5 THz. The output power level and the operation frequency are records for wideband photodiodes operating at 1.55 µm. Devices integrating resonant narrowband dipole antennae have also been fabricated and the output power increases at resonant peak frequencies confirmed. The device having a peak at 1.04 THz exhibits a maximum (detected) output power of 10.9 µW at 1.04 THz with good linearity. This output power is the highest value ever directly generated from a photodiode in the THz range, and several times higher than the maximum value reported by the low-temperature-grown GaAs photoconductive switch at around 1 THz.

No abstract

The photoresponse of a uni-traveling-carrier photodiode (UTC-PD), which is configured with a neutral narrow-gap light absorption layer and a depleted wide-gap carrier collecting layer, is investigated by small-signal analysis. Drift-diffusion model was used for analyzing carrier dynamics in the absorption layer. For accurately predicting the frequency response, a boundary condition at the edge of the absorption layer was carefully treated by taking into account the electron thermionic emission velocity. High electron mobility in the absorption layer and high drift velocity in the carrier collecting layer associated with the velocity overshoot effect are both essential for short response times. Calculations performed on InP/InGaAsP UTC-PDs with the same absorption and carrier collecting layer thicknesses show that the response can be dominated by the electron transport in the absorption layer provided that the significant velocity overshoot occurs in the carrier collecting layer. Furthermore, a UTC-PD with a quasi-field in the absorption layer can generate a several times broader bandwidth than conventional pin PDs, while maintaining a similar internal quantum efficiency.

No abstract