  We study a thin film growth model with temperature activated diffusion of
adsorbed particles, allowing for the formation of overhangs and pores, but
without detachment of adatoms or clusters from the deposit. Simulations in
one-dimensional substrates are performed for several values of the
diffusion-to-deposition ratio R of adatoms with a single bond and of the
detachment probability epsilon per additional nearest neighbor (NN),
respectively with activation energies are Es and Eb. If R and epsilon
independently vary, regimes of low and high porosity are separated at 0.075 <
epsilon_c < 0.09, with vanishingly small porosity below that point and finite
porosity for larger epsilon. Alternatively, for fixed values of Es and Eb and
varying temperature, the porosity has a minimum at Tc, and a nontrivial regime
in which it increases with temperature is observe above that point. This is
related to the large mobility of adatoms, resembling features of equilibrium
surface roughening. In this high-temperature region, the deposit has the
structure of a critical percolation cluster due to the non-desorption
condition. The pores are regions enclosed by blobs of the corresponding
percolating backbone, thus the distribution of pore size s is expected to scale
as s^{-tau} with tau ~ 1.45, in reasonable agreement with numerical estimates.
Roughening of the outer interface of the deposits suggests Villain-Lai-Das
Sarma scaling below the transition. Above the transition, the roughness
exponent alpha ~ 0.35 is consistent with the percolation backbone structure via
the relation alpha = 2-d_B, where d_B is the backbone fractal dimension.
