Low-Noise Avalanche Photodiodes for Midwave Infrared (2 to 5 um) Applications

In this program, we will develop room-temperature avalanche photodiodes (APDs) for midwave infrared (MWIR) applications. The internal gain of APDs results in significant improvements in optical receiver sensitivity, and APDs have been widely used for telecommunications receivers with In(0.53)Ga(0.47)As absorption regions lattice-matched to InP substrates. However, In(0.53)Ga(0.47)As is transparent to wavelengths longer than 1.65 um, and to date, APDs have not been available for the MWIR because materials that exhibit strong MWIR absorption also generate high dark currents at fields required for impact ionization. We propose a novel MWIR APD design that will maintain low noise, good responsivity, and high gain-bandwidth product. The device will employ the separate absorption, charge, and multiplication (SACM) structure widely used for telecommunications receivers coupled with several critical new design features: (1) an ultra-low-noise impact ionization engineered (I2E) multiplication region and (2) an undepleted absorber structure that will facilitate the incorporation of (3) an absorption region optimized for MWIR detection. For the absorption region, we will study Sb-based bulk materials such as InGaAsSb and InAsPSb as well as Sb-based strain-compensated quantum well structures. For the multiplication region, we will use compositions compatible with the GaSb-based absorption regions, such as AlGaAsSb, and apply these materials in the design of an I2E multiplication region.