The worldwide first all-fiber THz time-domain spectrometer for operation at 1.5 microm is presented. Applications up to 3 THz are demonstrated. Key devices are photoconductive antennas based on novel LT InGaAs/InAlAs multi-layer structures.
Mesa-structuring of InGaAs/InAlAs photoconductive layers is performed employing a chemical assisted ion beam etching (CAIBE) process. Terahertz photoconductive antennas for 1.5 microm operation are fabricated and evaluated in a time domain spectrometer. Order-of-magnitude improvements versus planar antennas are demonstrated in terms of emitter power, dark current and receiver sensitivity.
Undoped Ga0.47In0.53As layers were grown by molecular beam epitaxy lattice matched to InP at substrate temperatures, Ts, in the range from 100 to 600 °C. X-ray diffraction indicated a widening of the vertical lattice parameter and a simultaneous increase of the arsenic content at low growth temperature. The epitaxial layers were single-crystalline down to Ts=125 °C. The room-temperature residual carrier concentrations and the related mobilities for layers grown below 350 °C are strongly affected by Ts, whereas at 77 K an influence of Ts on these parameters is already visible at 450 °C. At the very low growth temperatures the epitaxial layers show highly conductive behavior attributed to defect induced ionized deep centers.
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