Dual-Carrier High-Gain Low-Noise Superlattice Avalanche Photodiodes

In this paper, novel avalanche photodiode structures with alternate carrier multiplication nanometer regions, placed next to a wider electron multiplication region, to create dual-carrier feedback systems, are proposed. Gain and excess noise factor of these structures are calculated based on the dead space multiplication theory under uniform electric field. In addition, the equivalent impact ionization ratios are derived and compared. It is observed that the proposed structures can generate much higher gain compared with conventional pure electron multiplication structures under the same electric field without severely degrading the excess noise quality. Excess noise is further optimized with careful adjustment of thin multiplication regions' thicknesses. These high-gain structures can operate under low-bias (<; 5 V) conditions, making it possible to integrate infrared avalanche photodiodes (APDs) directly into silicon read-out circuits. In this paper, type-II mid-wavelength infrared InAs/GaSb strained layer superlattice is used for simulation. However, the concept of dual-carrier APDs, with carrier feedback to generate high gain and control of excess noise through confining impact ionization in thin layers, is general and can also be applied to other wavelength APDs with different materials and thicknesses. Type II InAs/GaSb strain layer superlattice allows for versatile band structure design leading to impact ionization coefficient engineering.