A generalized method of DC and high-frequency analysis lor microwave transit time diodes in mixed tunnelling and avalanche mode, which can be applied to any type of diode Structure is reported. Taking a purely field-dependent tunnel generation rate for electrons, the same is computed lor holes from a simulated energy band diagram within the depletion layer of the diode. The method has been applied to a variety of Si, GaAs and InP diode structures. The results show a substantial degradation of IMPATT properties due lo phase distortion caused bv the tunnelling current.

The resJ ts of accurate and realist:c high-frequency numerical analysis of a si.icon DAR (double avalanche region) diode indicate some unique and useful m crowave characteristics. The DAR diode under any structural condition exhibits multioand microwave negative resistance cnaracteristics between 8 and 350 GHz which WoJld make it possible to realize w.de-band microwave oscillations (8 to 350 GHz) from any s:ngle OAR diode witn a mulrituning facility. The negat.ve resistance space distribution profiles of the diode at h:gh frequencies of operation shows near sinusoidal variation, bhich suggests that a OAR diode can have several 0ptimt.m diode widths for generation of a paflicular frequency. The results have been explained on the bas3 of computation of the total avalanche delay produced in both avalanche regions and transit time delay produced in the drift region.

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A realistic and accurate computer method for high frequency numerical analysis under small signal conditions of a double avalanche region (DAR) ( n + p v n p + ) lmpatt diode is described. The method is used to determine microwave properties of several silicon OAR diodes under various operating conditions. The results indicate t h e existence of discrete and widely separated negative conductance bands in t h e DAR diode which can provide selective tuning in addition to wide frequency coverage for t h e device. The magnitude of DAR negative conductance, which is found to be smaller by an order of magnitude than that for the corresponding double drift diode, can be enhanced by the introduction of suitable asymmetry in the doping concentration of n and p of the DAR diode structure. The common drifl layer for both types of charge carriers in the case of a OAR diode would result in space charge wave cancellation which may make it possible to push the input current to a high value and reduce t h e noise generation. Thus, a OAR diode may provide an appreciable amount of microwave power with low noise level over several frequency bands covering a wide frequency range.

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