Highly Uniform Photo-Sensitivity of Large-Area Planar InGaAs p-i-n Photodiodes With Low Specific Contact Resistance of Gallium Zinc Oxide

In this letter, we report the large-area planar-type InGaAs p-i-n photodiodes (PDs) by using gallium-doped zinc oxide (GZO) transparent conducting oxide as a lateral carrier-conducting layer for reduction in the lateral resistance of p⁺-InP contact layer and improvement in the uniformity of photo-sensitivity. After the 400 °C post-annealing, the GZO/p⁺-InP contact exhibits an ohmic characteristic and a low specific contact resistance of 8.2 × 10^-4 Ω · cm² with the transmittance over 85% in the wavelength range of 0.90-1.65 μm. The 800-μm-diameter PD exhibits a low dark current of 24 pA (5 nA/cm²) at -10 mV, a cutoff wavelength of 1.65 μm, a photo-responsivity of 1 A/W at the wavelength of 1.55 μm, and a quantum efficiency of ~80% in the wavelength range of 1-1.55 μm. In addition, the photo-sensitivity of PD in the light-received area exhibits highly uniformity even under high optical power. It is attributed to the use of GZO film as a lateral carrier-conducting layer.