Preparation and characterisation of Au/InGaP/GaAs Schottky barriers for radiation damage investigation

High quality Au/InGaP Schottky diodes have been prepared as efficient test structures for a study of the radiation hardness of InGaP as space solar cell material. A detailed characterisation of the metal–semiconductor barriers obtained on both n (free carrier concentration ranging from 3×l015 to 1.2×l018 cm−3) and p-type (3.5×1017 cm−3) InGaP epitaxial layers lattice matched to GaAs substrate has been performed using current–voltage, capacitance–voltage and internal photoemission techniques. Excellent electrical properties were found for low doped (ideality factor of 1.05–1.06, rectification ratio of about 1010 at 0.7 V, reverse current lower than 1×10−12 A at −2 V) as well as heavily doped samples (rectification ratios of about 105 at 0.6 V). The barrier height values calculated by the different techniques were compared and discussed. Deep level transient spectroscopy (DLTS) spectra obtained on unirradiated samples did not show detectable deep levels with the exception of the heaviest doped sample showing a weak peak associated to the DX centre. After electron irradiation at 9 MeV with doses ranging from 5×l013 to 1.5×1015 e cm−2 the samples exhibited a broad dominant peak (activation energy in the 0.90–0.93 eV range) whose intensity increased linearly with the absorbed dose. The broadening of the peak and the observed increase of the corresponding trap concentration with the doping level suggest that this peak could be associated to complexes due to the interaction of primary defects, created by high irradiation energy, with each others and with the shallow impurities.