Electrical Instability in Half‐Insulating GaAs

Energy spectrum and capture cross sections of local electronic states have been investigated in half‐insulating (oxygen‐doped) GaAs. The resulting spectrum of energy levels gave us a possibility to offer a general scheme of arising of negative differential conductance (DNC) for recombination non‐linearity; this scheme includes in particular two mechanisms discussed earlier [1, 2]. It was shown that in the case investigated the DNC appears as a result of recharging of impurity levels under the action of electric field. To study the effect of a uniformly distributed electric field upon semiconductor, high frequency field was employed; with the help of it we have obtained a falling region on volt‐ampere characteristic. If constant electric field is applied to the sample, a domain instability can be observed under conditions when mean field corresponds to the ohmic part of I‐U characteristic of a uniform sample; the smallest field corresponding to instability could vary within wide limits, depending on the situation at the cathode. Conceptions are developed about creation of a high‐field space charge region next to the cathode, where field reaches the value sufficient for displaying of DNC mechanism. Some information is obtained on the initial phase of creation of such a region under different conditions.