The band structure, density of states, optical properties, effective masses and loss function of Al<sub>x</sub>Ga<sub>1−x</sub>As and In<sub>y</sub>Ga<sub>1−y</sub>As were performed by the first-principles method within the local density approximation. The calculated direct band gap of the AlAs, Al<sub>0.5</sub>Ga<sub>0.5</sub>As, GaAs, In<sub>0.5</sub>Ga<sub>0.5</sub>As and InAs were 1.608 eV, 1.34eV, 1.02eV, 0.646eV and 0.316eV at G point, which were direct bandgap semiconductor materials. In addition, dielectric functions, the absorption function, refractive index, loss function and effective mass were analyzed in detail. The effective masses of Al<sub>x</sub>Ga<sub>1−x</sub>As and In<sub>y</sub>Ga<sub>1−y</sub>As were small, so they have high carrier mobility. These results make them to be promising candidates for future electronics.
A Ge-on-SOI uni-traveling carrier (UTC) photodetector was reported for high-power high-speed applications. The performances, in terms of dark-current, photocurrent responsivity and 3-dB bandwidth, were characterized for analog and coherent communications applications. The responsivity was 0.18 A/W at 1550 nm. The detector with a 40μmdiameter demonstrated an optical bandwidth of 2.72 GHz at -5V for 1550nm. The -1dB compression photocurrent at 1 GHz under -7V for 40μm-diameter device was about 16.24mA, the RF output power came to be 4.6 dBmw.