Avalanche photodiode thirty-two-element linear array with minimal dead space

A method of fabricating avalanche photodiode arrays with minimal dead space between adjacent elements is described. The method consists of incorporating an integrated array of lenses, thereby reducing the effective dead region from ~50 microm to a few microns. The method is demonstrated with a thirty-two-element linear array on 150-microm centers. If suitably antireflection coated, this array could be made with an external quantum efficiency of over 80% at any desired wavelength from 0.4 to 0.95 microm. For narrow bandwidths the detector noise is the limiting factor. For wider bandwidths the detector is primarily noise-in-signal-limited. The measured optical and electrical crosstalk is about -40 dB for bandwidths up to ~10 MHz. The gain uniformity, as measured with a 10-microm spot, is about +/-20% within an element and +/-30% over the whole array at an average gain of 60.