Abstract
Mostly, optical spectroscopies are used to investigate the physics of excitons, whereas their electrical evidences are hardly explored. Here, we examined a forward bias activated differential capacitance response of GaInP/AlGaInP based multi-quantum well laser diodes to trace the presence of excitons using electrical measurements. Occurrence of “negative activation energy” after light emission is understood as thermodynamical signature of steady state excitonic population under intermediate range of carrier injections. Similar corroborative results are also observed in an InGaAs/GaAs quantum dot laser structure grown by molecular beam epitaxy. With increasing biases, the measured differential capacitance response slowly vanishes. This represents gradual Mott transition of an excitonic phase into an electron-hole plasma in a GaInP/AlGaInP laser diode. This is further substantiated by more and more exponentially looking shapes of high energy tails in electroluminescence spectra with increasing forward bias, which originates from a growing non-degenerate population of free electrons and holes. Such an experimental correlation between electrical and optical properties of excitons can be used to advance the next generation excitonic devices.
Highlights
When a material is either optically or electrically excited, negatively charged electrons and positively charged holes can pair together under mutual Coulomb attraction to form “positronium” like bound quasiparticle states, called excitons.1–4 At low charge carrier densities, exciton as a composite boson of two fermions can either move freely or form localized complexes inside a solid
Similar corroborative results are observed in an InGaAs/GaAs quantum dot laser structure grown by molecular beam epitaxy
Normal bias activation behavior with increasing charge injection inverts after light emission and exhibits “negative activation energy” around some intermediate injection levels. We argue that this can be attributed to the presence of a “stable” steady state population of transitional bound states having estimated binding energy similar to those of weakly confined excitons in GaInP/AlGaInP multi quantum well (MQW) laser diodes
Summary
When a material is either optically or electrically excited, negatively charged electrons and positively charged holes can pair together under mutual Coulomb attraction to form “positronium” like bound quasiparticle states, called excitons. At low charge carrier densities, exciton as a composite boson of two fermions (eÀ and hþ) can either move freely or form localized complexes inside a solid. At higher densities and low enough temperatures, excitons are expected to form condensed phases of matter like Bose Einstein Condensation (BEC) of excitons and exciton-polaritons, BCS like superconducting states with excitonic pair formations in momentum space, and electron–hole liquid.. At higher densities and low enough temperatures, excitons are expected to form condensed phases of matter like Bose Einstein Condensation (BEC) of excitons and exciton-polaritons, BCS like superconducting states with excitonic pair formations in momentum space, and electron–hole liquid.17,18 Many of these phenomena are finding applications in novel devices like ultralow threshold excitonpolariton lasers.. Many of these phenomena are finding applications in novel devices like ultralow threshold excitonpolariton lasers.19–22 These excitons undergo excitonic Mott transition from a neutral excitonic phase to a conducting electron-hole plasma (EHP) phase at higher densities. Even at room temperature, the formation of excitons can influence optical spectra of semiconductor quantum structures
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