Comparison of Oxygen Ion and Proton Implanted GaAs Photoconductive Switches

On-wafer characterization of MMIC’s performed by optoelectronic techniques such as photoconductive sampling or electro-optic sampling is currently investigated by several groups1. For photoconductive sampling, pulse generation and/or waveform sampling are done by illuminating a photoconductive gap with short laser pulses. In order to integrate monolithically the photoconductive gaps and the device under test, the gaps have to be fabricated with a technology compatible with GaAs MMIC’s fabrication technology. In this work, we characterized and compared two such MMIC-compatible photoconductive gaps. For the photoconductive sampling technique, ultrafast carrier lifetime in the gap is required. A number of approaches2,3 have been tried to reduce carrier lifetime and achieve a higher bandwidth - sensitivity product. Radiation damaged material is commonly used but a major drawback for this approach is the poor sensitivity due to fewer carriers reach the contact and reduced mobility. An O+ implanted switch4,5, which is annealed at 410°C for 10 minutes after implantation to reduce defects has been developed to improve carrier mobility. The implantation was performed at two energies, 140 keV with a dose of 5 × 1011cm−2 and 360 keV with a dose of 1.3 × 1012cm−2. This process is compatible with TRW’s MMIC fabrication process. We characterized the O+ implanted GaAs switch and make a comparison with H + implanted GaAs switch.