Low temperature MBE-grown In(Ga,Al)As/InP structures for 1.55 μm THz photoconductive antenna applications

Low temperature MBE-grown In(Ga,Al)As materials on InP incorporating Be-doping feature extremely short optical response times down to the sub-ps range which is adequate for THz generation and detection in photoconductive antennas. However, very low resistivity of low temperature InGaAs is the main obstruction for the implementation in real THz antennas in the 1.55 mum wavelength range. The high conductive behaviour is due to the incorporation of growth induced defect states close to the conduction band acting as donors. Resistivity was increased in a twofold manner: firstly, by compensation with carefully balanced Be incorporation, and secondly by using additionally a novel layer sequence exploiting trapping centres in cladding layers. Specially designed periodic InGaAs/InAlAs multi-layer structures were grown, where the deep electron traps in the InAlAs material increase the resistivity of the multi-layer structure beyond 10⁶ Omega/sq. The combination of high resistivity behaviour and simultaneously sub-ps response time allows the fabrication of photoconductive THz antennas for the 1.55 mum range based on low temperature InGaAs/InAlAs multi-layer structures. These elements, similar to low temperature GaAs in the 850 nm range, represent a key element for compact THz systems making use of mature telecom components.