Effect of Ge-composition on the frequency response of a thin layer Si1−yGey avalanche photodiode

Bandwidth calculation of Si_1-yGe_y n⁺-i-p⁺ avalanche photodiode (APD) is described for multiplication layer down to tens of nanometers considering dead-space effect. In the analysis, the depletion region is discretized into equal energy segments to take into account the discontinuous nature of impact ionization in the multiplication layer due to dead-space effect, and carrier diffusion from undepleted regions is considered to study the effect of low bias on the frequency response. Carrier distribution within the structure is obtained by numerical solution of coupled equations and recurrence relations. The computed results are used to investigate the effect of Ge-composition (y) on the bandwidth of a Si_1-yGe_y APD having thin multiplication layer. Results show that at high gain region, for a fixed applied bias, frequency response decreases with the increase in Ge-content. It is also seen that at moderate gain region, if the bandwidth is RC dominated then the bandwidth decreases with increase in Ge-content.