Abstract

We solve the coupled transport equations of the electron and hole currents for an avalanche photodiode (APD) of arbitrary structure and determine its time and frequency response. The injection can be localized to one or both ends of the multiplication region, or it can be distributed throughout an extended region, as in the case of thermal or photoinduced generation. The electron and hole ionization rates can be arbitrary functions of position. Because the equations contain position-dependent coefficients, they are difficult to solve. Our approach is to divide the device into incremental layers within each of which the ionization rates are assumed constant. We solve the transport equations within each of these layers and obtain the overall solution by matching the results at the layer boundaries. The total current is then determined as a function of time by integrating the electron and hole current densities over the depletion-layer width. We apply the solutions to superlattice multiple-quantum-well and conventional multiple-layered APD's; we study the effects of the carrier ionization rates and the type and position of the injected carriers, as well as the layout of the device, on the gain and bandwidth.

© 1990 Optical Society of America