A theoretical and experimental study of the collection of charge carriers produced within and outside the space-charge region of a p-n-type solid-state radiation detector by an incident energetic alpha particle of 4.98-MeV energy is described. The depth of the space-charge region was made smaller by a variable forward-bias voltage externally applied. The magnitude of the applied voltage was smaller than the barrier potential. Measurements were made of the number of collected carriers from inside and outside the space-charge region as the depth of space-charge region was varied over the range of the incident alpha particle. The measured results show agreement with the theoretical considerations. Alpha-particle energies of 4.67, 3.87, 2.98, and 2.31 MeV were also investigated, but are not reported because results were analogous to that shown for 4.98 MeV. The collection efficiency of the detector was also investigated and is given, independent of the particle energy, as a function of the applied bias voltage.