P-type hyperdoped germanium (Ge) has attracted significant attention for the development of superconducting semiconductors. However, the limited solid solubility of acceptors, especially boron (B), in Ge makes hyperdoping challenging. Herein, a systematic study on the electrical properties of boron-implanted germanium is presented with an atomic concentration beyond 10 at%. The B-implanted Ge was annealed by millisecond flash lamp annealing (ms-FLA) with different parameters. The results indicate that millisecond solid phase epitaxy ensures the electrical activation of B much above the solubility limit with hole concentration as high as 2 × 10²¹ cm⁻³ and low-temperature sheet resistance of 13 Ω sq⁻¹ which is promising for superconductivity. It is also shown that millisecond annealing effectively suppresses the B diffusion and provides much higher activation efficiency of acceptors compared to conventional annealing methods.