Photocapacitance Studies of the Oxygen Donor in GaP. I. Optical Cross Sections, Energy Levels, and Concentration

Photocapacitance studies in GaP p-n junctions have given new insight to the deep states associated with the O donor. In addition to the well-known neutral state in which O binds an electron by 0.9 eV, a new state in which O deeply binds a second electron was discovered. The second electron is captured into a level {~} 0.45 eV deep, after which lattice relaxation increases the average optical-ionization energy to {~} 2.0 eV. The role of lattice relaxation was established by studying the temperature dependence of the photoionization of the trapped electrons. Profile measurements of the O-donor density through the depletion layer indicated a decrease in O-donor concentration from 1.5×{}10¹⁶ on p to 4×{}10¹⁴ on the n side. Optical cross sections and thermal-emission rates of both electrons were measured. Both electrons were stable below 100 ^∘{}C.