Spectroscopic studies in InGaN quantum wells

S. F. Chichibu, T. Sola, K. Wada, S. P. Denbaars, S. Nakamura

Research output: Contribution to journalConference article

Abstract

Fundamental electronic modulations in strained wurtzite III-nitride, in particular InxGa1-xN, quantum wells (QWs) were treated to explore the reasons why practical InGaN devices emit bright luminescences in spite of the large threading dislocation (TD) density. The emission mechanisms were shown to vary depending on the well thickness L and InN molar fraction x. The electric field across the QW plane, F, which is a sum of the fields due to spontaneous and piezoelectric polarization and the pn junction field, causes the redshift of the ground state resonance energy through the quantum confined Stark effect (OCSE). The absorption spectrum is modulated by QCSE, quantum-confined Franz-Keldysh effect (QCFK), and Franz-Keldysh (FK) effect from the barriers when, for the first approximation, potential drop across the well (F×L) exceeds the valence band discontinuity, ΔEv. Under large F×L, holes are confined in the triangular potential well formed at one side of the well. This produces apparent Stokes-like shift in addition to the in-plane net Stokes shift on the absorption spectrum. The QCFK and FK further modulate the electronic structure of the wells with L greater than the three dimensional (3D) free exciton (FE) Bohr radius, aB. When F×L exceeds ΔEC, both electron (e) and hole (h) confined levels drop into the triangular potential wells at opposite sides of the wells, which reduces the wavefunction overlap. Doping of Si in the barriers partially screens the F resulting in a smaller Stokes-like shift, shorter recombination decay time, and higher emission efficiency. Finally, the use of InGaN was found to overcome the field-induced oscillator strength lowering due to the spontaneous and piezoelectric polarization. Effective in-plane localization of the QW excitons (confined excitons, or quantized excitons) in quantum disk (Q-disk) size potential minima, which are produced by nonrandom alloy potential fluctuation enhanced by the large bowing parameter and F, produces confined e-h pairs whose wavefunctions are still overlapped when L<aB. Their Coulomb interaction is more pronounced for F×L<ΔEv.

Original languageEnglish
Pages (from-to)G2.7
JournalMaterials Research Society Symposium - Proceedings
Volume537
Publication statusPublished - 1999 Dec 1
Externally publishedYes
EventProceedings of the 1998 MRS Fall Meeting - Symposium on 'GaN and Related Alloys' - Boston, MA, USA
Duration: 1998 Nov 301998 Dec 4

ASJC Scopus subject areas

  • Materials Science(all)
  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering

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    Chichibu, S. F., Sola, T., Wada, K., Denbaars, S. P., & Nakamura, S. (1999). Spectroscopic studies in InGaN quantum wells. Materials Research Society Symposium - Proceedings, 537, G2.7.