Conduction current injection delay in Read GaAs IMPATT diodes

We find experimentally that, for GaAs Read avalanche diodes, the optimal drift region width is not simply inversely proportional to optimum frequency. This finding can be understood by noting that the injection phase of the avalanche current into the drift region is not 90° with respect to the voltage maximum, but varies as a function of frequency. The experimental observations are in reasonable agreement with solutions of the Read equation which include the reverse junction saturation current. The theoretical fit to the data is relatively insensitive to the avalanche intrinsic response time, and thus we cannot make an independent determination of its value at present.