Prof Michael Johnston

Abstract:

We demonstrate enhancement of terahertz (THz) emission from indium arsenide at 170 K in magnetic fields (B) up to 8 T. An order of magnitude increase in visible to terahertz conversion efficiency was observed, with no suggestion of saturation of the TE polarization at higher magnetic fields. Free-space electro-optic sampling measurements confirmed the coherent nature of this radiation over the field range investigated, and gave an insight into the carrier motion subsequent to photoexcitation, which may be responsible for the observed THz power enhancement. © 2000 American Institute of Physics.

Abstract:

The intermixing technique was used to modify the energy level distribution of GaAs/AlGaAs quantum-wells so as to change the photoelectric characteristics of the photodetector. A large response wavelength shift was achieved by the proton implantation followed by standard annealing procedures (950°C for 30s). The measurement results show that (1) PL and photoresponse spectra are the function of ion dose in the range from 5×1014/cm2 to 2.5×1015/cm2; (2) the peak photoresponse wavelength is tunable between 8.4 μm and 10.2 μm for the infrared; (3) the PL peak for the related material changes from 1.62 eV to 1.645 eV. The influence on responsivity and dark current was analyzed.

Abstract:

The effects of magnetic fields up to 8T on the THz emission from a bulk (100) n-type molecular beam epitaxy (MBE)-grown GaAs sample were studied. Magnetic field was applied in the plane of incidence parallel to the reflected THz beam. The emitted THz radiation was measured both by an incoherent bolometer detection scheme and coherent free-space electro-optic (EOS) sampling. Overall, significant data was obtained.