Evolution of superclusters and delocalized states in GaAs1−xNx

Abstract

The evolution of individual nitrogen cluster bound states into an extended state infinite supercluster in dilute GaAs 1-x N x was probed through temperature and intensity-dependent, time resolved and magneto-photoluminescence (PL) measurements.Samples with compositions less than 0.23% N exhibit PL behavior that is consistent with emission from the extended states of the conduction band. Near a composition of 0.23% N, a discontinuity develops between the extended state PL peak energy and the photoluminescence excitation absorption edge. The existence of dual localized/delocalized state behavior near this composition signals the formation of a N supercluster just below the conduction band edge.The infinite supercluster is fully developed by 0.32% N.2

Optical density of states in ultradilute GaAsN alloy: Coexistence of free excitons and impurity band of localized and delocalized states

“…If the free-exciton transition arising from the hybridized conduction band due to alloying in GaAs 1Àx N x identified with the 1.450 eV peak, one infers x % 0.25%. 16,23 The structure in the transitions below 1.408 eV is attributed to phonon replicas. This is discussed in detail later.…”

“…[1][2][3][4][5]10 After 15 years of intensive study, the recent interest in GaAs 1Àx N x has shifted to focusing on N concentrations less than 0.5% for understanding how the band structure evolves as one goes from the very heavy doping (parts per hundred thousand) to the dilute alloy (parts per hundred) limit. [14][15][16][17][18][19] This paper discusses the nature of light emitting states in ultra-dilute GaAs 1Àx N x observed through a very complex emission spectrum. We will present strong evidence for the existence of both localized and delocalized states within the continuum of states forming the defect band, [18][19][20] address the controversy whether the low energy peaks in the emission spectra are phonon-assisted transitions or from a separate set of cluster states, [21][22][23] and finally discuss the quantum mechanical enhancement of the excitonic oscillator strength on account of the localization of its center of mass.…”

Magnetic-Field-Induced Delocalized to Localized Transformation in GaAs:N

“…8 Recent experimental results 9,10 reveal that the optical properties are profoundly altered when the localized cluster states overlap and percolate into a fully extended infinite supercluster, which hybridizes with the host conduction band states. 11,12 This percolation threshold is manifested in a massive and abrupt linewidth broadening of the E 0 and E 1 critical point energies that correspond to interband transitions at the Γ and X points of the Brillouin zone, respectively, and signals the evolution of the impurity-doped semiconductor into an alloy 9,10 Unfolding the statistical evolution of N cluster states and their influence on the electronic and optical properties of GaAs:N is hampered by the difficulty in probing resonant impurity states as well as supercluster bound states. 7 At the higher doping concentrations (> 0.23% N) when the cluster states begin to exert a dominant influence on the electronic bandstructure, line broadening and spectral overlap obscures attempts at unraveling the individual cluster identities within a supercluster.…”

“…Our approach now makes it possible to elucidate the evolution of N superclusters right through the onset of the percolation threshold. 9,10 Dilute GaAs 1-x N x films were grown by molecular beam epitaxy (MBE) up to thicknesses of 300 nm. The compositions ranged between 0.04% and 0.41% N and were confirmed with x-ray diffraction measurements.…”

Raman Scattering Signature of a Localized-to-Delocalized Transition at the Inception of a Dilute Abnormal GaAs1-xNxAlloy

“…2,16) The question is whether Raman scattering, particularly, resonance Raman scattering, would be able to shed light on the nature of this transition. Indeed, we observe that the E W energy changes abruptly between the concentrations of 0.41 and 0.32% as shown in Fig.…”