Excess Noise Characteristics of Thin AlAsSb APDs

Characterization of AlAsSb avalanche photodiodes (APDs) with avalanche region widths
w
of 80 and 230 nm showed that electron ionization coefficient is slightly higher than that for hole. The avalanche gain at a given bias is marginally higher under pure electron injection, achieved using 442-nm laser, compared to those measured under mixed carrier injections using 542- and 633-nm lasers. Low-excess-noise factors were measured, corresponding to the lines of
k
= 0.1,
k
= 0.15, and
k
= 0.21, where
k
is the effective ionization coefficient ratio, for the APDs with
w
= 80 nm. Under the same carrier injection conditions, the APDs with
w
= 230 nm exhibit even lower noise corresponding to
k
= 0.05,
k
= 0.12, and
k
= 0.17. The lowest excess noise achieved, with
k
= 0.05, is significantly lower than those obtained in InP and InAlAs APDs with the same
w
.