Minority-carrier dynamics in semiconductors probed by two-photon microscopy

TL;DR

This paper develops an analytical model for two-photon microscopy in semiconductors, revealing how diffusion, bulk, and surface recombination affect carrier dynamics and photoluminescence decay.

Contribution

It provides the first analytical solution to a 3D diffusion equation for two-photon microscopy in semiconductors, including effects of a buried interface.

Findings

Bulk measurements are dominated by diffusion at short times.

Long-time decay is governed by bulk recombination.

Surface recombination impacts signals near interfaces.

Abstract

Two-photon time-resolved photoluminescence has been recently applied to various semiconductor devices to determine carrier lifetime and surface recombination velocities. So far the theoretical modeling activity has been mainly limited to the commonly used one-photon counterpart of the technique. Here we provide the analytical solution to a 3D diffusion equation that describes two-photon microscopy in the low-injection regime. We focus on a system with a single buried interface with enhanced recombination, and analyze how transport, bulk and surface recombinations influence photoluminescence decays. We find that bulk measurements are dominated by diffusion at short times and by bulk recombination at long times. Surface recombination modifies bulk signals when the optical spot is less than a diffusion length away from the probed interface. In addition, the resolution is increased as the spot size is reduced, which however makes the signal more sensitive to diffusion.