  The phosphide-based III-V semiconductors InP, GaP, and In$_{0.5}$Ga$_{0.5}$P
are promising materials for solar panels in outer space and radioisotope
batteries, for which lifetime is a major issue. In order to understand high
radiation tolerance of these materials and improve it further, it is necessary
to describe the early stages of radiation damage on fast time and short length
scales. In particular, the influence of atomic ordering, as observed e.g. in
In$_{0.5}$Ga$_{0.5}$P, on electronic stopping is unknown.We use real-time
time-dependent density functional theory and the adiabatic local density
approximation to simulate electronic stopping of protons in InP, GaP, and the
CuAu-I ordered phase of In$_{0.5}$Ga$_{0.5}$P across a large kinetic energy
range.These results are compared to SRIM and we investigate the dependence on
the channel of the projectile through the target.We show that stopping can be
enhanced or reduced in In$_{0.5}$Ga$_{0.5}$P and explain this using the
electron-density distribution. By comparing Ehrenfest and Born-Oppenheimer
molecular dynamics, we illustrate the intricate dynamics of a proton on a
channeling trajectory.
