On response time of semiconductor photodiodes

Alexander O Goushcha,Bernd Tabbert

doi:10.1117/1.oe.56.9.097101

Abstract

The effect of displacement currents due to dielectric relaxation of majority carriers in the charge-neutral region of a semiconductor photodiode is discussed. The dielectric relaxation is often neglected when treating the response time of photodiodes. We show that this component may dominate the slow response of not fully depleted photodiodes and has to be taken into account for correct analysis of silicon photodiode response to a brief laser pulse. A phenomenological expression for the photodiode response time that accounts for the displacement current effects is proposed and used to compare with the experimental results.

Highlights

The response time to a brief external injection of excess carriers through light absorption is one of the most important figures of merit of optical detectors, including semiconductor photodiodes and photoconductors
The drift component τdrift of the photodiode response time is conventionally defined as the time required for the nonequilibrium minority and majority carriers to reach the edges of the space-charge region
In many cases the numbers for the photodiode response time obtained using Eq (1) are close to the measured 10% to 90% rise/fall time values, the description of processes involved as given by Eq (1) may not always be correct

Summary

Introduction

The response time to a brief external injection of excess (nonequilibrium) carriers through light absorption is one of the most important figures of merit of optical detectors, including semiconductor photodiodes and photoconductors. In case of a pulsed source of light, the detector response time is considered as either the rise time or fall time required for the output signal to change from 10% to 90% of its final value or vice versa. Both the rise and fall time depend on the RC time constant (τRC 1⁄4 RC) of the detector and time required to collect nonequilibrium carriers by the external electrodes. The drift component τdrift of the photodiode response time is conventionally defined as the time required for the nonequilibrium minority and majority carriers to reach the edges of the space-charge region. The diffusion component τdiff of the photodiode response time is defined conventionally as the time required for both minority and majority carriers to reach the edges of the charge-neutral region of the semiconductor

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