An ultra-efficient internal mechanism to amplify photoresponse for Si and compound semiconductor devices

Optical imaging and detection systems use photodetectors to turn optical signals into electric signals and use electronic amplifiers to increase the signal intensity. If the detector can produces sufficient gain by itself, the sensitivity can no longer be limited by the thermal noise of electronics. Instead, the system sensitivity will be limited by the shot noise of the detector characterized by the excess noise factor. The most prominent example is avalanche photodetector (APD) where signal amplification is achieved by the intrinsic process of impact ionization. However, although APD based photoreceiver shows the best sensitivity for fiber optic communications, it has high excess noise and requires high operation voltage (50-200V for Si APDs). This presents the need for an entirely new intrinsic signal amplification mechanism in semiconductors, which leads to the discovery and invention of the cycling excitation process (CEP) mechanism. CEP for signal amplification can be realized in a heavily doped and highly compensated Si p-n junction as illustrated in Fig. 1(a), so that an energetic electron (hole) can excite an e-h pair from a localized impurity state via the Auger process as shown in Fig. 1(b). Note that the carrier in the localized impurity gives rise to a high uncertainty in momentum, thus relaxing the momentum conservation or k-selection rule. This new amplification process cannot be completed without the specific electron-phonon interaction shown in Fig. 1(c). Hence the gain is regulated by phonons, which provide the “intrinsic negative feedback” to stabilize the gain and reduce the excess noise.