This thesis presents work on two significant research areas in silicon photonics. The first is focused on improving the capability of using single crystal silicon for infrared photon detection. A vertically arrayed core- shell silicon nanowire device has been fabricated and characterized for the investigation of the bias dependence behavior of the sub-bandgap light detection. The intrinsic properties of the nanowire device are based on three physical mechanisms: Franz-Kelydsh effect, quasi-quantum confinement effect, and the impurity state assisted photon absorption. A detailed physical model incorporates all the three physical mechanisms has been developed to analyze its fundamental characteristics and an excellent agreement with the experimental data has been found. The second is on the discovery of a new photoresponse amplification mechanism in highly doped and heavily compensated silicon p-n junctions. The new gain mechanism has been investigated by measuring the photoresponse behavior of a simple planar mesa device. The distinctive characteristics of such an internal amplification mechanism include the gain occurs at bias voltage as low as -2 V and the amplified signal is enhanced rather than suppressed with increasing temperature. A physical model - cycling excitation process (CEP) has been proposed based on the experimental observations. Results from theoretical modeling, fabrication, and experimental measurements of these devices are discussed. In particular, the gain mechanism works in low voltage range and favors room temperature over cryogenic temperature, makes it promising for practical device applications

We report the experimental evidence of uncovering a photoresponse amplification mechanism in heavily doped, partially compensated silicon p-n junctions under very low bias voltage. We show that the observed photocurrent gain occurs at a bias that is more than an order of magnitude below the threshold voltage for conventional impact ionization. Moreover, contrary to the case of avalanche detectors and p-i-n diodes, the amplified photoresponse is enhanced rather than suppressed with increasing temperature. These distinctive characteristics lead us to hypothesize that the inelastic scattering between energetic electrons (holes) and the ionized impurities in the depletion and charge neutral regions of the p-n junction in a cyclic manner plays a significant role in the amplification process. Such an internal signal amplification mechanism, which occurs at much lower bias than impact ionization and favors room temperature over cryogenic temperature, makes it promising for practical device applications.

Signal amplification, performed by transistor amplifiers with its merit rated by the efficiency and noise characteristics, is ubiquitous in all electronic systems. Because of transistor thermal noise, an intrinsic signal amplification mechanism, impact ionization was sought after to complement the limits of transistor amplifiers. However, due to the high operation voltage (30-200 V typically), low power efficiency, limited scalability, and, above all, rapidly increasing excess noise with amplification factor, impact ionization has been out of favor for most electronic systems except for a few applications such as avalanche photodetectors and single-photon Geiger detectors. Here, we report an internal signal amplification mechanism based on the principle of the phonon-assisted cycling excitation process (CEP). Si devices using this concept show ultrahigh gain, low operation voltage, CMOS compatibility, and, above all, quantum limit noise performance that is 30 times lower than devices using impact ionization. Established on a unique physical effect of attractive properties, CEP-based devices can potentially revolutionize the fields of semiconductor electronics.