When an avalanche photodiode (APD) is operating at a sufficient reverse bias, the photo-generated carriers can reach the depletion region to induce a multiplication process. The asymmetry of the electron and hole in mercury cadmium telluride (MCT) in effective mass may result in unequal ionization coefficients and provide a single carrier induced impact ionization process. Thus, an electronic avalanche photodiode (EAPD) with ``ideal'' APD characteristics including near noiseless gain can be formed. At abroad, the MCT/FAPD devices with high gain (～7?10^3), low excess noise factor close to unity, THz gain-bandwidth product and fast response in the level of picoseconds are fabricated for various detector applications involving low photon numbers. The fundamental issues, device architectures, technology development and performance of MCT/EAPD are reviewed.