Dielectrics for passivation of planar InP/InGaAs diodes

Dielectrics were investigated for passivating planar InP or InGaAs photodiodes: thermally evaporated Al2O3 and SiO, sputtered Si3N4 and SiO2 and also SiO2 using chemical vapour deposition. The measured bulk and field-effect properties of all dielectrics excluding sputtered SiO2 were suitable for this application. In planar InGaAs diodes with Cd diffused or Mg implanted p+-region a disordered dielectric/semiconductor surface led to high reverse current densities above 1 mA/cm2. In InP diodes with p+-diffusion and dielectrics exhibiting positive flatband voltages, eg Si3N4 and Al2O3, reverse current densities of 10 mu A/cm2 were measured probably caused by a slight inversion of the semiconductor surface. With a SiO or CVD-SiO2 passivating layer on n-InP lowest leakage current densities (10 nA/cm2) were achieved. Very low dark-current planar photodiodes InP/InGaAsP/InGaAs have been fabricated using SiO passivation (30 nA/cm2).