ABSTRACT
Luminescence techniques belong to the most sensitive, nondestructive methods of semiconductor research. The most widely performed experiments in spectroscopy are transmission, re¯ection, and luminescence spectroscopy. Other techniques include, e.g., photoluminescence excitation spectroscopy, ellipsometry, modulation spectroscopy, measurements of the luminescence yield, or Raman spectroscopy. The standard setup for optical spectroscopy consists of a light source, the sample under investigation, usually placed in a cryostat, a monochromator to disperse the light, and a detection unit. Luminescence spectra usually give information on the deepest radiative states of a system including their optical phonon replica or acoustic phonon wings. At low temperatures, these are often defect states or localized states resulting from some disorder like spatial ¯uctuations of the width of a quantum well or of the composition of alloys. At higher temperatures also, extended states become accessible in luminescence. The absorption and re¯ection spectra give information of optically allowed transitions from the occupied ground state into excited states. Fabry-Perot modes, which appear often in quantum structures due to parallel surfaces or interfaces of substrate, buffer layers, etc., can be used to determine the
CONTENTS
11.1 Introduction to Spectroscopy ...................................................................425 11.2Band Structure of GaN..............................................................................426 11.3Optical Transitions in GaN without Impurities ....................................427 11.4 Optical Transitions in GaN under the Impact of Impurities ...............428 11.5 Interpretation of GaN Luminescence Spectra .......................................429 11.6 Impact of Threading Dislocation in GaN ...............................................438 11.7Luminescence of GaN Layers Grown in Nonpolar Directions ...........438 References .............................................................................................................440
