STEADY-STATE DISTRIBUTIONS OF THE FIELD AND SPACE-CHARGE IN THE INTERIOR OF THE I-LAYER IN A GAAS P-I-N STRUCTURE

An optical method for observing electric fields which is based on the Franz-Keldysh effect has been used to study the steady-state field dis tribution in a p-i-n structure based on lightly doped GaAs at reverse bias voltages from 10 to 140 V. The field distribution in the interior of the structure varies in a qualitative way with U. At U > 60 V, fre e carriers are completely removed from the interior of the i layer by the field, so the field has an absolute maximum at the middle of the i layer. The field distribution is determined by the net charge bound a t donor and acceptor levels which are highly depleted throughout the v olume of the i layer. Their concentration has a nonuniform spatial dis tribution. At U < 60 V, the free carriers are not completely removed. There is a nonuniform spatial filling of impurity levels. The sign of the space charge changes near the boundaries of the i layer. The field in this case has maxima at the boundaries and a minimum at the middle of the i layer. The observed field distributions are analyzed theoret ically. The results are compared with experimental data.