Large-Area Planar Wavelength-Extended InGaAs p-i-n Photodiodes Using Rapid Thermal Diffusion With Spin-On Dopant Technique

In this letter, we report the large-area planar-type 2.2- $\mu \text{m}$ wavelength-extended InAsP/InGaAs/InAsP p-i-n photodetectors (PDs) using the rapid thermal diffusion (RTD) technique. The zinc-phosphorous-dopant-coating was used as the spin-on dopant source, which was driven into the InAsP/InGaAs heterostructure to form the p-type cap layer of p-i-n diode through the RTD process. The Si/Al 2 O 3 bilayers were deposited as the antireflective coating to improve the responsivity of vertically illuminated the PDs. The 800- $\mu \text{m}$ -diameter PD exhibits a low dark current of $4.1\,\times \,10^{\mathrm {\mathbf {-8}}}$ A ( $8.2\,\times \,10^{\mathrm {\mathbf {-6}}}$ A/cm $^{\mathrm {\mathbf {2}}}$ ) at −10 mV, a cutoff wavelength of 2.2 $\mu \text{m}$ , a quantum efficiency of above 90% in the wavelength range of 1.4–2.0 $\mu \text{m}$ , and a high responsivity of 1.45 A/W at 2- $\mu \text{m}$ wavelength at room temperature. In addition, the PD exhibits good uniformity in the light received area in the illuminated power range of 0.1–2.0 mW.