A low-noise, high-gain, and high-bandwidth avalanche photodiode (APD) structure is described. The device is a variation of the p-i-n doped quantum well structure that is expected to show four orders of magnitude enhancement in the carrier ionization rates. In practice, p-i-n doped quantum well devices are difficult to realize owing to the difficulty in achieving highly doped n-type AlGaAs. A structure in which the doped layers are formed in GaAs rather than in AlGaAs, but in which the performance features of the doped AlGaAs devices are retained, is described. The device consists of repeated unit cells of an intrinsic Al/sub 0.45/Ga/sub 0.55/As layer followed by p-i-n-i doped GaAs layers. Calculations based on many-particle ensemble Monte Carlo simulation of the electron and hole ionization rates as a function of the device parameters are presented, illustrating the basic design criteria.< >