ZnSe-based MBE-grown photodiodes

ZnSe p-i-n-type photodiodes were grown on GaAs substrates using molecular beam epitaxy technique. ZnCl 2 was used for n-doping and plasma-excited N 2 for p-doping. The p-side contact consists of 200 nm Au in situ deposited on a 20 nm highly doped ZnTe layer on top of the p-doped ZnSe forming a well-defined Schottky barrier, as can be confirmed by current - voltage measurements together with an electrical model of the diode. Reverse-bias photocurrent was measured as a function of wavelength. The spectral responsivity is about 30 mA (WeV) at the band edge which corresponds to a quantum efficiency of roughly 8%. Calculations of the spectral response were performed using a modified model originally designed on Si solar cells and reflectivity data determined by ellipsometry. The comparison of the model with measurements indicates that the photocurrent is dominated by the drift current generated within the space-charge region.