Nitrogen ion implanted ZnSe/GaAs p-i-n photodetectors

p-i-n photodiodes were fabricated on nitrogen ion implanted undoped ZnSe/n-type ZnSe epilayers grown on w + GaAs (100) substrates by molecular beam epitaxy. To obtain a quasi-uniform p layer doping profile, nitrogen ions at multiple energies and ion doses were implanted at room temperature. The activation of implanted species was carried out by an optimized post-annealing in a nitrogen ambient. Optical studies were performed on the implanted/annealed devices by photoluminescence spectroscopy at 10 K, which indicated donor-acceptor pairs at an energy of 2.7 eV and its phonon replicas with 30 meV intervals. The circular p-i-n diodes with a 1 mm diam contact area showed a device breakdown voltage to be linearly dependent on the thickness of the undoped ZnSe epilayer. For p-i-n diodes fabricated on an initial 0.5 μm thick undoped ZnSe layer, an ideality factor of 1.19 and a reverse bias breakdown voltage of 12 V was observed. A large photocurrent, good linearity with light intensity, and low dark current were observed. A photocurrent/dark current ratio > 10⁵ was obtained at an illumination intensity of 100 mW/cm². These devices exhibited a responsivity of 0.025 AAV at a wavelength of 460 nm through the top 200 A thick metal contacts.