Ionization-Enhanced AlGaN Heterostructure Avalanche Photodiodes

A heterostructure multiplication region consisting of high/low-Al-content AlGaN layers instead of the conventional high-Al-content AlGaN homogeneous layer was proposed to increase the average hole ionization coefficient and to realize a higher gain in AlGaN avalanche photodiodes (APDs) based on separate absorption and multiplication structures. The fabricated APDs with the Al _0.2 Ga _0.8 N/Al _0.45 Ga _0.55 N heterostructure multiplication region exhibit very steep breakdowns and a maximum gain of $5.5\times 10^{4}$ at a reverse bias of 109 V. Meanwhile, the large potential barrier to the conduction band formed at the Al _0.2 Ga _0.8 N/Al _0.45 Ga _0.55 N heterostructure interface can suppress the electron-initiated multiplication, and hence, reduce the noise of the APDs by impeding the transport of electrons. The simulation of noise confirms this effect from the heterostructure.