Oxygen DX center in In0.17Al0.83N: Nonradiative recombination and persistent photoconductivity

Abstract

Using a hybrid density-functional scheme, we address the O impurity substitutional to N (O N ) in In 0.17 Al 0.83 N. Our modelling supports In clustering to account for the strong band-gap bowing observed in In x Al 1-x N alloys. To study the O N defect in In 0.17 Al 0.83 N alloys, we therefore consider a model containing an In cluster and find that the most stable configuration shows four In nearest neighbors. We show that such a O N defect forms a DX center and gives rise to two defect levels at 0.70 and 0.41 eV below the conduction band edge, in good agreement with experiment. The calculated defect energetics entail a fast nonradiative recombination upon photoexcitation at room temperature and account for the observation of persistent photoconductivity at low temperature.PACS numbers: 71.55. Eq,61.72.uj In the last decades, In x Al 1-x N has attracted a great deal of interest for its possible applications in electronic and optoelectronic devices. 1-3 In particular, In 0.17 Al 0.83 N is nearly lattice matched to GaN and can be used to realize strain-free heterostructures. 4,5 Applications include distributed Bragg reflectors, thick cladding layers in edge emitting lasers, waveguides exploiting the large difference in refractive indices between InAlN and GaN, and high-electron mobility transistors (HEMTs). [6][7][8] To control the electronic properties of these materials, it is important to understand the role of impurities. Upon growth through metalorganic vapor phase epitaxy (MOVPE), it is known that considerable concentrations of oxygen and carbon impurities are incorporated. 8 Experimental investigations have identified various defect states with activation energies ranging between 200 and 500 meV. 9-11 However, their origin has been difficult to ascertain and it has remained unclear whether these states relate to point defects or to dislocations. More recently, defect states have been measured at 68 meV and 270 meV and tentatively assigned to oxygen on the basis of their concentration. 12 The observation of persistent photoconductivity (PPC) effects has been taken as an indication supporting this interpretation, 12 as oxygen is known to give rise to DX centers in AlN. 13 In this Letter, we study the oxygen impurity substitutional to nitrogen (O N ) in In 0.17 Al 0.83 N through densityfunctional-theory calculations. We find that O N gives defect levels that are in agreement with experimental observations. These impurities behave like DX centers and can explain the origin of the persistent photoconductivity effects.In our calculations, we make use of the semilocal density functional introduced by Perdew, Burke, and Ernzerhof (PBE), 14 and of the hybrid functional introduced by Heyd, Scuseria, and Ernzerhof (HSE). 15,16 In the latter, the fraction of Fock exchange is set to α = 0.37 for AlN and to α = 0.19 for InN, in order to reproduce their experimental band gaps. For intermediate In x Al 1-x N alloys, the mixing coefficient α is linearly interpolated.We use normconserving pseudopotentials to treat corev...

Effects of growth temperature on structural and electrical properties of in-rich InAlN–GaN heterostructures by radio-frequency metal–organic molecular beam epitaxy

“…There is the behavior of spontaneous polarization charge differences of between the InAlN and GaN layers at room temperature. Also, earlier studies was indicated that high carrier concentration of InAlN film is induced by unintentional oxygen doping [38]. In addition, oxygen impurities were incorporated at grain boundaries, which has been related to an increase in the bandgap energy of InAlN films deposited [39].…”