Abstract
Photoluminescence (PL) spectroscopy is a powerful tool in studying semiconductor properties and identifying point defects. Gallium nitride (GaN) is a remarkable semiconductor material for its use in a new generation of bright white LEDs, blue lasers, and high-power electronics. In this Tutorial, we present details of PL experiments and discuss possible sources of mistakes. A brief analysis of near-band-edge emission includes basic characterization of GaN, essential findings about excitons in this material, and the explanation of less known details. We review modern approaches of quantitative analysis of PL from point defects in GaN. The updated classification of defects in undoped GaN and their latest identifications are presented. Typical mistakes in the interpretation of PL spectra from GaN are discussed, and myths about PL are refuted.
Highlights
Luminescence is one of the primary research methods and characterization techniques in studies of semiconductor materials
HdFgeCre1⁄4, SEe0*iÀs hthωeemHuisantgh–eRFhryasnfka–ctCoornidnotnhesehxifctiteind state the of the defect; ground state; E0* 1⁄4 E0 þ 0:5hΩe is the distance from the n = 0 level to the ground-state parabola at Q = Q0; E0 is the zero-phonon line (ZPL) energy; hΩe is the energy of the effective phonon mode in the excited state; and hω and hωem are the photon energy and position of the PL band maximum, respectively
In Gallium nitride (GaN) samples co-doped with C and Si, or Zn and Si, the CN-related YL1 band redshifts by 0.1 eV with decreasing Pexc from 0.1 to 10−4 W/cm2.138 It is important to notice that only PL bands caused by electron transitions from the conduction band or from shallow donors in GaN demonstrate giant shifts due to electric fields
Summary
Luminescence is one of the primary research methods and characterization techniques in studies of semiconductor materials. The term photoluminescence (PL) will be solely used hereafter This Tutorial focuses on PL from point defects in semiconductors and uses GaN as a case study. Semiconductors include wide-bandgap materials and insulating crystals, such as GaN, AlN, BN, ZnO, and Ga2O3. The wide bandgap, strong PL, sensitive detectors for the photon energies of interest, and high quality of GaN samples make this material advantageous for studying point defects. Significant progress in the understanding of point defects in GaN has been achieved after our previous review paper.[1] Many findings reviewed in this Tutorial are relevant for other semiconductors and insulators, especially direct-gap materials. There will be no discussion of GaN-based alloys, structures, and nanostructures Other luminescence techniques such as cathodoluminescence, electroluminescence, and optically detected magnetic resonance are beyond this article’s scope. Tutorials on point defects in semiconductors studied by other methods are available.[4,5,6,7] We will use the acronyms in Table I throughout this article
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