Abstract
Impact ionization in 1–2.5 μm thick AlxGa1−xAs/GaAs multiple quantum well (MQW) avalanche photodiodes with various barrier and well widths has been investigated in detail. The measured avalanche multiplication suggests that in all cases no enhancement of the ionization coefficients over that of equivalent GaAs is possible. Excess noise measurements on these structures corroborate the multiplication results and show that no enhancement of the ionization coefficient ratio can be obtained in AlxGa1−xAs/GaAs MQWs by virtue of the heterojunction interfaces, irrespective of the number of repeating units. These results suggest that the excess energy gained by carriers crossing the AlxGa1−xAs/GaAs heterojunction interface is negligible and that the lower ionization coefficients of the AlxGa1−xAs results in behavior that is similar to that of a pseudoalloy of the wells and barriers.
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