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There have been numerous reports on the practical limitations of conventional p+-n-n+ avalanche diodes. These reports conclude that large-signal power saturation occurs at about 35% voltage modulation in silicon and at a somewhat higher level in gallium arsenide. This power saturation can, to a large extent, be attributed to the losses incurred in the diode, owing to the effective series resistance of unswept epitaxial material, an effect that necessarily occurs at large voltage swings. This depletion-layer modulation also gives rise to detrimental parametric effects under large-signal conditions. The letter briefly reviews the prime causes of this power saturation, and explains how voltage modulation in excess of 75% may be obtained, without any depletion-layer modulation, by using a 4-layer structure. Conversion efficiencies exceeding 55% can be obtained, while retaining the advantages of the p+-n-n+ structure.