Two-terminal multi-color photodetectors and focal plane arrays

Abstract

Two-terminal multi junction photodetectors and focal plane arrays for multi-color detection or imaging acquisition can be formed by connecting photodiodes with different bandgaps or wavelengths, through tunnel diodes, in series with the same polarization. Under reverse bias in the dark, the total current going through such multi junction photodetectors is dictated by the smallest reverse saturation current of the photodiodes. When in operating mode, a set of light sources with different wavelengths corresponding to each individual photodiode can be used to optically bias all the photodiodes except the detecting photodiode Under illumination, all other photodiodes work in the photovoltaic mode and have much higher maximum possible reverse currents than the detecting photodiode. As a result, the total current of the multi junction photodetector is dictated by the detecting photodiode. Therefore, a total current can be read by, for example, read-out circuits to give the optical signal strength at that specific wavelength of the detecting photodiode. By using an algorithm one can use such multi junction photodetectors to detect different wavelengths and to take multicolor images.