This paper reviews the research into and development trends to date of high-speed high-sensitivity semiconductor superlattice (SL) avalanche photodiodes (APDs) for use in 1.3 to 1.55 mu m wavelength optical communications. We focus on three types of SL-APDs based on an InAlGaAs-well/InAlAs-barrier structure. The first is an InAlGaAs/ InAlAs polyimide-coated mesa-structure SL-APD with a high gain-bandwidth product of over 120 GHz and a low multiplied dark current of a few tens of nano-amperes. Its reliability has been measured to be over 10(5) h at 50 degrees C. The second is a planar-structure SL-APD with a new titanium-implanted guard-ring; this structure has a longer lifetime than the mesa structure. The third is a large-receiving-area SL-APD integrated with a monolithic lens for eye-safety 1.5 mu m wavelength optical measurement systems. References: 46
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