GaAs/GaAlAs superlattice avalanche photodiode at wavelength λ = 0.8 μm

Abstract

In a fiber optic communication system, the receiver must have high gain and low noise. The latter is generated in the photodetector, the load resistor, and the preamplifier. The photodetector 'gain' can be improved by use of an Avalanche Photodiode (APD) in which an internal gain is obtained from the impact ionization multiplication process. If, however, the ionization rates of electrons ((alpha) ) and holes ((beta) ) have the same value, the noise associated to the multiplication process will be high, according to McIntyre theory. This means that most of the III-V semiconductors are unsuitable for APD with low noise because (alpha) and (beta) are about the same. One way to improve the noise performance of the III-V compound semiconductor APDs is to alter the ratio (beta) /(alpha) (or (alpha) /(beta) ) by the use of a multi-quantum well (MQW) structure in the multiplication region of the APD. For a GaAs/GaAlAs MQW superlattice there is a large difference between the conduction and the valence band discontinuities ((Delta) Ec and (Delta) Ev) at the GaAs-GaAlAs edges. (Delta) Ec higher than (Delta) Ev leads to (alpha) >(beta) : electrons have more ability than holes to impact ionize. The authors obtained from multiplication factors and noise measurements a ratio k^-1 equals (alpha) /(beta) equals 8...10, which is similar to the value given by F. Capasso.