Time-resolved photoluminescence studies of Al-rich AlGaN alloys

J. Li, K. B. Nam, T. N. Oder, K. H. Kim, M. L. Nakarmi, J. Y. Lin, H. X. Jiang

Research output: Contribution to journalConference article

1 Scopus citations

Abstract

Si-doped n-type AlxGa1-xN alloys with x up to 0.5 and Mg-doped p-type AlxGa1-xN alloys with x up to 0.27 were grown by metal-organic chemical vapor deposition (MOCVD) on sapphire substrates. For the n-type AlxGa1-xN, we achieved highly conductive alloys for x up to 0.5. An electron concentration as high as 1 × 1018 cm-3 was obtained in Si-doped Al0.5Ga0.5N alloys with an electron mobility of 16 cm2/Vs at room temperature, as confirmed by Hall-effect measurements. Our results also revealed that (i) the conductivity of AlxGa1-xN alloys continuously increases with an increase of Si doping level for a fixed value of Al content (x < 0.5), (ii) the conductivities of AlxGa1-xN alloys decrease with increasing Al content for a given doping level; (iii) the critical Si-doping concentration needed to convert insulating AlxGa1-xN with high Al contents (x ≥ 0.4) to n-type conductivity is about 1 × 1018 cm-3. Time-resolved photoluminescence studies carried out on these materials have shown that Si-doping reduces the effect of carrier localization in AlxGa1-xN alloys and a sharp drop in carrier localization energy occurs when the Si doping concentration increases above 1 × 1018 cm-3, which directly correlates with the observed electrical properties. For the Mg-doped AlxGa1-xN alloys, p-type conduction was achieved for x up to 0.27, as confirmed by variable temperature Hall measurements. Emission lines of band-to-impurity transitions of free electrons with neutral Mg acceptors as well as localized excitons have been observed in the p-type AlxGa1-xN alloys. The Mg acceptor activation energies EA were deduced from photoluminescence spectra and were found to increase with Al content and agreed very well with those obtained by Hall measurements. From the measured activation energy as a function of Al content, EA versus x, the resistivity of Mg-doped AlxGa1-xN with high Al contents can be deduced. Our results have also shown that PL measurements provide direct means of obtaining EA especially where this cannot be obtained accurately by electrical methods due to high resistance of p-type AlxGa1-xN with high Al content.

Original languageEnglish
Pages (from-to)250-257
Number of pages8
JournalProceedings of SPIE - The International Society for Optical Engineering
Volume4643
DOIs
StatePublished - 2002
EventUltrafast Phenomena in Semiconductors VI - San Jose, CA, United States
Duration: Jan 21 2002Jan 25 2002

Keywords

  • AlGaN
  • Optical transitions
  • Time-resolved PL
  • UV light emitters
  • Wide bandgap

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