The capability of growing long‐wavelength infrared HgCdTe liquid‐phase epitaxy P‐on‐n heterojunction films with state‐of‐the‐art photodiode performance, with excellent thickness uniformity (±10%), and with excellent cutoff wavelength uniformity (e.g., 10.5±0.1 μm) across 2.5 cm×4.0 cm wafers has been demonstrated. In addition, we have extended the region of HgCdTe photodiode operation to wavelengths of 18–19 μm at 80 K. Both measured carrier lifetime and photodiode data show that the n‐type HgCdTe base layers are of excellent quality, with 77 K carrier lifetimes at the calculated Auger‐1 limit for film carrier concentrations above 4×1014 cm−3. The R0A products for large‐area diodes (10−3 cm2 ) with cutoff wavelengths of 11–19 μm are consistent with n‐side diffusion current calculated using the film Auger‐1 lifetime. Smaller diodes of area 1×10−5 cm2 have typical R0A values of 12 Ω cm2 at 80 K for a 12.2 μm cutoff wavelength. Large area diodes with an 80 K cutoff wavelength of 18–19 μm have R0A products of...