Avalanche Photodiode Noise Research Articles

Enhancement of electron impact ionization in a superlattice: A new avalanche photodiode with a large ionization rate ratio

The first superlattice avalanche photodiode (APD) is reported. The high field region of this p-i-n structure consists of 50 alternating Al0.45Ga0.55As (550 Å) and GaAs (450 Å) layers. A large ionization rate ratio has been measured in the field range (2.1–2.7)×105 V/cm, with α/β≃10 at a gain of 10 giving a McIntyre noise factor Fn = 3. The ionization rate ratio enhancement with respect to bulk GaAs and AlGaAs is attributed to the large difference in the band edge discontinuities for electrons and holes at the heterojunction interfaces. The superlattice APD is a new device concept which can be used to develop low noise APD’s in a variety of III-V materials including long wavelength 1.3–1.6-μm semiconductors.

Timing error tolerant waveforms in optical fibre systems

The problem of pulse shaping and sensitivity to timing errors in optical fibre data communication is considered. The performance of the overall transmission system is the average probability of error, which is computed for intersymbol interference, thermal noise, and shot noise in avalanche photodiodes. An analysis of the immunity to small sampling errors of various Nyquist pulses indicates useful design criteria.

Low noise avalanche photodiodes by channeling of 800-keV boron into 〈110〉 silicon

Low noise avalanche photodiodes, which have an n+-p-π-p+ structure, are reported. Channeled boron ions (800 keV) in the 〈110〉 of Si are used for forming the p layer. The characteristics of this diode are compared with those fabricated by 800-keV random implantation. Low excess noise factors F=4–5 at a gain of 100 are obtained by using 〈110〉 channeled implantation, whereas F=6–7 for random implantation. By using parallel implantation, the uniformity of channeled distributions of boron ions are found to be fairly good at different locations in a wafer.

Avalanche-noise dependence on avalanche-photodiode structures

Excess avalanche-photodiode noise is calculated by considering photogenerated diffusion currents and photogenerated carrier distributions. Computed results reveal the effects of junction depth, depletion-layer thickness and incident light direction on avalanche noise for various optical-absorption coefficients.