Researchers at the University of California, Santa Barbara have developed a new avalanche photodiode that is low noise and provides a highly stable gain at small bias voltages. These favorable characteristics are achieved through a particular design of the multiplication layer of the device, which is constructed such that electron-hole pairs are created at specific depths and not re-absorbed after multiplication. This novel design produces a series of operating regions where the gain is relatively constant with the applied voltage, mitigating gain sensitivity. Moreover, the operating regions that correspond to constant gain exhibit extremely low noise, temperature, and voltage sensitivities. Operating voltages can be reduced to less than 10V, allowing these devices to be integrated with digital circuitry.

File Number: 21090 

Web site: http://techtransfer.universityofcalifornia.edu/...

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Background

Avalanche photodiodes (APDs) are photodetectors that provide a built-in first stage of gain through avalanche multiplication. By applying a high reverse bias voltage to the device (typically 100-200V in silicon), APDs show an internal current gain of approximately 100 due to the avalanche effect. In general, a higher reverse voltage yields a higher gain, and thus most modern APDs use alternative doping and/or beveling techniques to allow applied voltages > 1000V to achieve an operating gain > 1000. The drawback of existing APDs is that the multiplication factor is strongly dependent upon the applied electric field strength, temperature, and doping profile; thus, they are more sensitive in terms of both noise and stability. As a result, there is a clear need for APDs that provide stable gain at lower operating voltages.