PIN photodiodes using nitrogen ion implantation on ZnSe/GaAs heterostructure

PIN photodiodes were fabricated by nitrogen ion implantation on undoped 0.5, 1.0, 1.5, and 2.0 μm thick ZnSe/n-ZnSe/n⁺GaAs(100) grown by molecular beam epitaxy (MBE). To obtain the p-layer, nitrogen ions at multiple energies and ion doses were implanted at room temperature to obtain a quasi-uniform doping profile. The activation of implanted ions was achieved by post-annealing in a N-ambient at 500°C for 5 min. Optical studies were performed by photoluminescence (PL) 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 PIN diodes with 1 mm diameter active area showed an ideality factor of 1.19 and reverse bias breakdown voltage of 10 V for 0.5 μm thick undoped ZnSe. Moreover, good linearity with light intensity, low dark current and high photocurrent were seen. A photocurrent/dark current ratio of more than 10⁴ for an illumination of 100 mW/cm² at a reverse bias of 1 V through a 200 Å thick metal layer was seen for the 0.5 μm thick layer. A responsivity of 0.025 A/W was obtained at a wavelength of 460 nm through the metal contacts.