Photoluminescence, Magnetospectroscopy, and Resonant Electronic Raman Studies of Heteroepitaxial Gallium Nitride


B.J. Skromme
Department of Electrical Engineering and Center for Solid State Electronics Research, Arizona State University

This article was received on Friday, October 8, 1999 and accepted on Friday, December 3, 1999.

Abstract

Optical spectroscopy, including low and room temperature photoluminescence (PL), reflectance, PL measurements in high magnetic fields up to 12 T, and resonantly-enhanced electronic Raman scattering (RERS) in zero and high magnetic field, has been used to investigate exciton and impurity states and surface recombination in high quality heteroepitaxial GaN grown on sapphire and SiC. Theoretical finite-difference calculations of the donor states as a function of magnetic field have been carried out for comparison, including the effects of anisotropy in the effective mass and dielectric constant. Up to six residual donor species are observed in material grown by hydride vapor phase epitaxy (HVPE) and metalorganic chemical vapor deposition (MOCVD) from their n=2 and n=3 two-electron satellites observed in PL and by RERS. The donor-related nature of the relevant transitions is confirmed from their magnetic field dependence, and the spectral resolution is improved at high fields. The Si donor level is determined to have a binding energy of about 21 meV from observation of its two-electron satellite in lightly Si-doped HVPE material. The free exciton binding energy is shown to be about 26.4 meV, independent of strain, based on observations of the n=2 free exciton. The room temperature band-edge PL peak is confirmed to be free excitonic in nature, based on its linewidth and on comparison with simple reflectance measurements. Reflectance from the edge of a thick HVPE layer shows clear evidence of A, B, and C excitons obeying the relevant selection rules at both low and room temperature. Surface chemical treatments are shown to have substantial effects on room temperature PL efficiency. Passivation with ammonium or sodium sulfide solutions, in particular, yields increases in PL efficiency by a factor of five to seven over air-exposed surfaces. The passivation effect is stable in air, lasting at least one month.

Outline

  • Introduction
  • Theoretical Calculation Of Donor States In GaN
  • Experimental Methods
  • Observation And Identification Of Shallow Donor Levels
  • Magnetospectroscopy of Two-Electron Transitions
  • Identification of the Si Donor Level
  • Electronic Raman Scattering from Shallow Donors
  • Comparison with Other Measurements
  • Free Exciton States at Low and Room Temperature
  • Chemical Treatment and Sulfide Passivation of GaN Surfaces
  • Conclusions
  • Acknowledgments

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    Cite this article as: MRS Internet J. Nitride Semicond. Res. 4, 15(1999).

    last updated Tuesday, June 26, 2001 11:56:17 PM.

    © 1999-2001 The Materials Research Society MRS Internet Journal of Nitride Semiconductor Research