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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.

Many time-domain terahertz applications require systems with high bandwidth, high signal-to-noise ratio and fast measurement speed. In this paper we present a terahertz time-domain spectrometer based on 1550 nm fiber laser technology and InGaAs photoconductive switches. The delay stage offers both a high scanning speed of up to 60 traces / s and a flexible adjustment of the measurement range from 15 ps -200 ps. Owing to a precise reconstruction of the time axis, the system achieves a high dynamic range: a single pulse trace of 50 ps is acquired in only 44 ms, and transformed into a spectrum with a peak dynamic range of 60 dB. With 1000 averages, the dynamic range increases to 90 dB and the measurement time still remains well below one minute. We demonstrate the suitability of the system for spectroscopic measurements and terahertz imaging.

We present first results on photoconductive THz emitters for 1.55µm excitation. The emitters are based on MBE grown In0.53Ga0.47As/In0.52Al0.48As multilayer heterostructures (MLHS) with high carrier mobility. The high mobility is achieved by spatial separation of photoconductive and trapping regions. Photoconductive antennas made of these MLHS are evaluated as THz emitters in a THz time domain spectrometer (THz TDS). The high carrier mobility and effective absorption significantly increases the optical-to-THz conversion efficiency with THz bandwidth in excess of 3 THz.

A modified photoconductive receiver significantly improves the performance of photomixing-based continuous wave (cw) THz systems driven at the optical telecommunication wavelength of 1.5 μm. The achieved signal-to-noise ratio of 105 dB at 100 GHz and 70 dB at 1 THz, both for an integration time of 200 ms, are to our knowledge the highest numbers reported in literature for any optoelectronic cw THz system, including classical setups operating at 800 nm. The developed receiver allows for combining low cost and high performance in one system for the first time to our knowledge.

We present results on optimized growth temperatures and layer structure design of high mobility photoconductive Terahertz (THz) emitters based on molecular beam epitaxy grown In0.53Ga0.47As/In0.52Al0.48As multilayer heterostructures (MLHS). The photoconductive antennas made of these MLHS are evaluated as THz emitters in a THz time domain spectrometer and with a Golay cell. We measured a THz bandwidth in excess of 4 THz and average THz powers of up to 64 μW corresponding to an optical power-to-THz power conversion efficiency of up to 2 × 10−3.

We investigate the influence of Beryllium (Be) doping on the performance of photoconductive THz detectors based on molecular beam epitaxy (MBE) of low temperature (LT) grown In(0.53)Ga(0.47)As/In(0.52)Al(0.48)As multilayer heterostructures (MLHS). We show how the optical excitation power affects carrier lifetime, detector signal, dynamic range and bandwidth in THz time domain spectroscopy (TDS) in dependence on Be-doping concentration. For optimal doping we measured a THz bandwidth in excess of 6 THz and a dynamic range of up to 90 dB.

Using indium as catalyst for growth and simultaneously as doping source, ordered arrays of n-type ZnO single crystal nanorods have been perpendicularly grown on p-GaN∕Al2O3 substrates with a vapor phase transport growth method. The low temperature photoluminescence measurements of the n-ZnO nanorods show dominant In-related neutral donor bound exciton emission in the ultraviolet region. Electrical transport measurements performed on single n-ZnO nanorods yield resistances of about 50–200kΩ and a typical specific resistivity of 2.0×10−2Ωcm. The resistivity is one order of magnitude reduced by introducing In compared to the nominally undoped ZnO nanorods.