Search

Suzuki et al. [18] reported THz emission from Fe ion implanted Ga0.47In0.53As PC antennas triggered by 1.56 μm excitation pulses. The radiated field from the Fe ion implanted Ga0.47In0.53As had a reduced pulse width compared to that obtained from the unimplanted emitters. This reduction in pulse width was attributed to the rapid relaxation of the carriers from the conduction state to the trapped state connected with the Fe ions and vacancies. It was also possible to apply a much higher bias voltage (~12 kV/cm) in the ion implanted material due to the increased resistivity. A linear dependence of the emitted THz radiation on the applied bias voltage was observed up to 12 kV/cm at an excitation power of 5 mW. As before, the THz emission was observed to saturate at higher pump powers. Suzuki et al. [19] also reported THz emission from unbiased Ga0.47In0.53As and Ga0.4In0.6As surfaces excited at 1.56 and 1.05 μm respectively. Similar saturation effects of the emitted THz field with increasing pump power were observed in this case also.

This dissertation contains results obtained from investigating pulsed THz emission characteristics of semi-large aperture photoconducting (PC) antennas fabricated on Fe-doped bulk Ga0.69In0.31As substrate. The research is aimed at evaluating the impact of physical properties of a semi-large aperture Ga0.69In0.31As PC antenna upon its THz generation efficiency, and is motivated by the ultimate goal of developing a pulsed THz radiation source with MHz repetition rates, capable of operating at wavelengths between 1 and 1.5 μm, and having an average output power of 1 mW.

The emission of terahertz (THz)-radiation pulses from binary and ternary narrow bandgap semiconductors is discussed. Ga x In 1−x As:Fe is a THz-emitter material for time-domain THz systems with potentially ≈1mW of average THz-radiation power at MHz repetition rates.

We report the study of terahertz emission from bulk GaxIn1-xAs crystals as function of semiconductor properties. We demonstrate that both optical rectification and ultrafast photocurrents contribute to terahertz emission depending on the Ga mole fraction and microcrystal size.

We report an experimental study of femtosecond optically excited emission of terahertz frequency electromagnetic radiation from ${\text{Ga}}_{x}{\text{In}}_{1\ensuremath{-}x}\text{As}$ bulk crystals with alloy composition in the range between $0lxl0.65$. The terahertz-emission mechanisms in bulk ${\text{Ga}}_{x}{\text{In}}_{1\ensuremath{-}x}\text{As}$ were studied as a function of carrier mobility, carrier concentrations, band gap as well as polycrystal grain size. Our experiments and analysis demonstrate that optical rectification is the dominant terahertz-emission mechanism for ${\text{Ga}}_{x}{\text{In}}_{1\ensuremath{-}x}\text{As}$ with $0.01\ensuremath{\le}x\ensuremath{\le}0.43$ while surface-field acceleration is dominant for ${\text{Ga}}_{x}{\text{In}}_{1\ensuremath{-}x}\text{As}$ with $0.43\ensuremath{\le}x\ensuremath{\le}0.64$. The magnitude of terahertz emission due to optical rectification is a function of the polycrystal grain size of the ${\text{Ga}}_{x}{\text{In}}_{1\ensuremath{-}x}\text{As}$ samples. Terahertz emission from ${\text{Ga}}_{x}{\text{In}}_{1\ensuremath{-}x}\text{As}$ due to optical rectification is due to a ${\ensuremath{\chi}}^{(2)}$ nonlinear optical process. Overall, terahertz emission from ${\text{Ga}}_{x}{\text{In}}_{1\ensuremath{-}x}\text{As}$ is maximized for $x\ensuremath{\approx}0.1--0.3$.

We report femtosecond transient reflectivity measurements of as-grown and iron-doped GaxIn1−xAs. A hybrid vertical Bridgman and gradient freezing directional solidification process was employed for the growth of high quality Ga0.69In0.31As:Fe crystals with the uniform impurity doping concentration necessary for high resistivity (1.6×107 Ω cm) and high mobility [(2–3)×103 cm2/V s] material. Carrier lifetimes range from ∼62 fs for as-grown Ga0.09In0.91As to ∼306 fs for Ga0.69In0.31As:Fe. The high carrier mobility along with high resistivity and subpicosecond carrier lifetimes make Ga0.69In0.31As:Fe an excellent candidate for photoconducting antenna based terahertz emitters.

We report measurements of terahertz (THz) frequency radiation pulses emitted by photoconducting (PC) antennas fabricated from high-resistivity Fe-doped Ga0.69In0.31As. The Ga0.69In0.31As:Fe was grown using a hybrid vertical Bridgman and gradient freezing directional solidification process. GaxIn1−xAs crystals were uniformly doped with Fe atoms to obtain high-resistivity (∼107 Ω cm). The ultrafast carrier mobility in this material is about three orders of magnitude higher than in GaxIn1−xAs thin films grown by molecular beam epitaxy. The bandgap of Ga0.69In0.31As:Fe is low enough (∼1 eV) to use compact Yb-based multiwatt lasers operating at 1.1 μm for photoexcitation of Ga0.69In0.31As based PC antennas for high power THz emission.