Power Dependence of the Photocurrent Lineshape in a Semiconductor Quantum Dot

TL;DR

This paper develops a kinetic theory to analyze how photocurrent lineshape in quantum dots depends on power, revealing a crossover point where kinetics dominate and showing how linewidth broadens with increasing power.

Contribution

It introduces a model linking photocurrent lineshape to tunneling rates and power, highlighting a crossover power and the effects of spin polarization in magnetic fields.

Findings

Photocurrent saturates above a critical power $P_c$ due to hole escape rates.

Linewidth increases with power as $ oot P$, indicating kinetic effects.

The spin-doublet lineshape reflects the incident light's polarization degree.

Abstract

We propose a kinetic theory to describe the power dependence, $I_{PC}(P)$, of the photocurrent (PC) lineshape in optically pumped quantum dots at low temperatures, in both zero and finite magnetic fields. We show that there is a crossover power $P_c$, determined by the electron and hole tunneling rates, at which the photocurrent spectra become strongly influenced by the dot kinetics, and no longer reflect the exciton lifetime in the dot. For $P>P_c$, we show that the photocurrent saturates due to the slow hole escape rate (in e.g., InGaAs/GaAs dots), whereas the line-width increases with power: $\Gamma \propto \sqrt{P}$. We also analyze to what measure the spin-doublet lineshape of the photocurrent studied in a high magnetic field reflects the degree of circular polarization of the incident light.