Electronic excitations stabilised by a degenerate electron gas in semiconductors

TL;DR

This paper reports the discovery of collexons, a new class of quasiparticles stabilized by a degenerate electron gas in heavily doped semiconductors, challenging previous expectations of exciton dissociation at high doping levels.

Contribution

It introduces collexons, a novel quasiparticle stabilized by many-particle effects in highly doped semiconductors, supported by experimental observations in germanium-doped GaN.

Findings

Observation of pronounced emission traces up to 100 K in heavily doped GaN.

Stabilization of collexons with increasing doping concentration.

High crystal quality enabled the detection of these quasiparticles.

Abstract

Excitons in semiconductors and insulators consist of fermionic subsystems, electrons and holes, whose attractive interaction facilitates bound quasiparticles with quasi-bosonic character due to even-numbered pair spins. In the presence of a degenerate electron gas, such excitons dissociate due to free carrier screening, leaving a spectrally broad and faint optical signature behind. Contrary to this expected behaviour, we have discovered pronounced emission traces in bulk, germanium-doped GaN up to 100 K, mimicking excitonic behaviour at high free electron concentrations from 3.4E19/cm3 to 8.9E19/cm3. Consequently, we show that a degenerate, three-dimensional electron gas stabilizes a novel class of quasiparticles, named collexons, by many-particle effects dominated by exchange of electrons with the Fermi gas. The observation of collexons and their stabilisation with rising doping concentration, is facilitated by a superior crystal quality due to perfect substitution of the host atom with the dopant.