Separate Absorption-Charge Multiplication Heterojunction Phototransistors With the Bandwidth-Enhancement Effect and Ultrahigh Gain-Bandwidth Product Under Near Avalanche Operation

We demonstrate a high-performance heterojunction phototransistor (HPT): separate absorption-charge multiplication HPT. The incorporation of an In
_0.52
Al
_0.48
As-based multiplication layer in the In
_0.53
Ga
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As-based collector layer of our HPT allows for a great shortening of the trapping time ( ~ ns to ~ 30 ps) of electrons at the base-emitter junction under near avalanche operation, without sacrificing the gain performance. The interaction between the photoconductive gain and avalanche gain means that it is not necessary to use high bias voltages (> 30 V ) in our device to attain high-gain (> 1times 10
⁴
) performance. With this device design, we can achieve an extremely high (90 THz) gain-bandwidth product (1.6 GHz, 5.5 times 10
⁴
) under a 6-V bias.