Ultrahigh B-doped Ge(001) layers, with concentrations C-B up to 8x10(21)cm(-3), were grown by gas-source molecular beam epitaxy from Ge2H6 and B2H6 at temperatures T-s=325 degrees C (in the surface-reaction-limited regime) and 600 degrees C (in the flux-limited regime). The samples were quenched, D site exchanged for H, and D-2 temperature-programed desorption (TPD) used to determine B coverages theta(B) as a function of C-B and T-s by comparison with B-adsorbed Ge(001) reference samples with known theta(B) values. During Ge(001):B film growth, strong surface B segregation to the second layer was observed with surface-to-bulk B concentration ratios ranging up to 6000. The TPD spectra exhibited alpha(2) and alpha(1) peaks associated with dideuteride and monodeuteride desorption as well as lower-temperature B-induced alpha(2)* and alpha(1)* peaks associated with deuterium desorption from Ge* surface atoms with B backbonds. Increasing theta(B) expanded the area under alpha(2)* and alpha(1)* at the expense of alpha(2) and alpha(1) and decreased the total. D coverage theta(D). The TPD results were used to determine the B segregation enthalpy, -0.64 eV, and to explain and model the effects of high B coverages on Ge(001) growth kinetics. At T-s = 325 degrees C, where B segregation is kinetically hindered, film deposition rates R-Ge are not a strong function of C-B, exhibiting only a small decrease at C(B)greater than or similar to 5x10(18)cm(-3). However, at T-s=600 degrees C, R-Ge decreases by up to 40% with increasing C(B)greater than or similar to 1x10(18)cm(-3). This is due primarily to the combination of B-induced Ge dimer vacancies and the deactivation of surface dangling bonds caused by charge transfer to Ge-B backbonds. Calculated R-Ge(C-B, T-s) curves, based upon equilibrium segregation, exhibit very good agreement with deposition rate data at T-s = 600 degrees C and overestimate the effect of B on R-Ge at 325 degrees C.