Analysis and evaluation of uniformity of SWIR InGaAs FPA—Part I: Material issues

The nonuniformity caused by fluctuations of indium composition, thickness and doping concentration of epitaxial absorption layer of InGaAs focal plane arrays (FPAs) is estimated theoretically with the incorporation of practical status. By the measurements on epitaxy wafers of 2 in. size, the fluctuation of indium composition is observed to be less than ±0.2% and ±1% for lattice matched In0.53Ga0.47As and wavelength extended In0.80Ga0.20As photodetector structures respectively, while the thickness and doping fluctuations are assumed to be the same. Results show that the response nonuniformity caused by fluctuation of indium composition is dependent on the target wavelength and can be neglected with a minor composition fluctuation if the cutoff wavelength is well set. The total response nonuniformity induced by the effects of thickness and doping fluctuations, which dominates the FPA performance for large signal applications, is estimated to be less than ±0.1% and ±0.5% for In0.53Ga0.47As and In0.80Ga0.20As FPAs smaller than 1 in. in maximum side length. Neglecting the effects of defects, the total detectivity nonuniformity caused by these fluctuations is about ±2% for In0.53Ga0.47As FPA and will reach up to about ±19% for In0.80Ga0.20As FPA, where the dark current nonuniformity due to the fluctuation of composition plays the most critical role.