Electrical characteristics of HgCdTe Schottky diode photo-detectors with passivation layers transparent to free carriers
The characterization and fabrication of Schottky diodes based on Hg1−xCdxTe for x ≈ 0.2 are presented. In order to reduce or eliminate Fermi level pinning a passivation dielectric layer was specially grown on the metal–semiconductor interface. Its thickness had to be reduced to allow for free carrier tunnelling. Dielectric layers composed of native oxides, native fluorides, SiO2 or Al2O3 were investigated. Interface trap density of less than 3 × 1011 cm−2 eV−1 and interfacial layer charges of less than 1 × 1011 cm−2 were obtained. Diode characterization was performed by analysing I/V characteristics. The barrier heights for different metals, penetration coefficient for free carrier tunnelling through the dielectric potential barrier and diode ideality factor for different dielectric layer thicknesses were estimated. The barrier height showed pronounced dependence on the metal applied. The best results for an ideality factor of 1.5 were achieved with the Schottky diode samples passivated with native fluoride, the values for other dielectrics being smaller than 3. High values for diode differential resistance were obtained.