We have investigated the carrier concentration profiles in molecular-beam epitaxy-grown, Si-implanted, low-temperature (LT) GaAs. The samples were grown at 300degreesC and the Schottky diodes were fabricated using An contacts. The capacitance voltage measurements were made in the temperature range 100-350 K at an interval of 2 K. From the field-effect transient spectroscopy experiments, data were collected for the peak positions and peak energy of the trap levels. The effective carrier concentration increased with temperature showing a saturation around 350 degreesC. The ionization energy of the carriers indicated a linear relationship. The overall results indicate that the carrier concentration in three-dimensional mapping is a reliable indicator of the sample quality and of the Schottky diode characteristics. Additionally, one should be specific about the temperature and the reverse bias voltage before selecting the value of the carrier concentration when determining the deep trap concentration in semiconductors, specifically, in LT GaAs.