High-Performance Ge p-n Photodiode Achieved With Preannealing and Excimer Laser Annealing

A germanium (Ge) n⁺/p shallow junction photodiode fabricated by a combination of low-temperature preannealing and excimer laser annealing of the phosphorus-implanted p-type Ge is demonstrated. The Ge photodiode shows a high responsivity of 0.48 A/W at the 1.55-μm wavelength and an extremely low leakage current density of 1 pA/μm² at room temperature, over two orders of magnitude lower than that of diodes formed by the rapid thermal annealing process. In addition, the reverse leakage current is close to the theoretical limitation of Ge diodes dominated by the ideal carrier diffusion model. The well-controlled dopant profile of the Ge shallow junction should be beneficial for improving the performance of the diodes, which may also be used in making the source and drain of scaled Ge nMOSFET.