Unlike GaAs which is p type, InP, when doped with the amphoteric C, is known to exhibit n-type conduction but with a low carrier-to-dopant ratio. To learn more about C behavior, we have intentionally introduced atomic H in C-doped n-InP by exposing the samples to a radio-frequency deuterium plasma. We show here that C, unlike other n dopants (S, Sn, and Si), strongly interacts with H in InP. First, the distribution of deliberately introduced H closely follows that of C. Second, for all C dopings studied here, the H concentration is nearly equal to that of C. Finally, and most importantly, the electrical properties of the material are also significantly altered, for instance, the free-electron concentration increases by more than an order of magnitude in certain samples. © 1998 American Institute of Physics.