Attollo proposes to develop GeSn/Si heterojunction APDs by employing semiconductor grafting techniques that was invented by our partner Prof. Zhenqiang (Jack) Ma at University of Wisconsin. The band offset between Ge0.9Sn0.1 and Si is about zero eV, allowing electrons to be collected in the avalanche Si region without any energy barrier, which is ideal for APD applications. Note that the proposers have checked 6 other types of possible material candidates with > 2µm absorption that can also be grafted with Si by Prof. Ma at UW-Madison, including Ga0.34In0.66As, In0.73As0.27P, Hg0.58Cd0.42Se, and others. All of these candidates have a negative band offset with Si, thus forming an electronic energy barrier for electrons to be collected by Si for multiplication.
