Luminescence from growth topographic features in GaN : Si films

Cathodoluminescence (CL) in the scanning electron microscope is used to investigate the nature of defects responsible for the luminescence associated with round and hexagonal-like topographic features of GaN:Si films. Round hillocks of the size of a few microns, which sometimes have a nanopipe related central hole, do not influence the luminescence emission of the film. Hillocks with sizes of several tens of microns show a marked CL contrast at the center and at the border. The origin of the observed contrast is attributed to a growth induced inhomogeneous distribution of point defects and impurities. Radiation with the electron beam of the scanning microscope causes a decrease of the CL intensity without spectral changes

Effect of laser irradiation on the luminescence of Mg and Si-doped GaN films

Pulsed laser treatments have been performed in GaN samples of both n- and p-type conductivity. The laser induced changes have been monitored by emissive mode and cathodoluminescence (CL) in a scanning electron microscope. Emissive mode observations indicate a moderate laser induced recrystallization. The luminescent emission has been characterized in both types of samples, GaN:Si and GaN:Mg. Whereas the evolution of CL in the Si doped samples could be explained by the occurrence of laser induced annealing, the luminescent behavior of the Mg doped samples upon irradiation seems to be more complex and a strong relation with the compensation or Mg activation is suggested. Several luminescence bands with maxima ranging from 3.3 to 2.7 eV and their dependence on irradiation conditions have been studied

Study of defects in GaN films by cross-sectional cathodoluminescence

Cathodoluminescence (CL) in the scanning electron microscope has been used to study cross-sectional samples on GaN epitaxial films grown on sapphire. Increased CL emission, attributed to the presence of stacking faults and decorated dislocations, is observed in a region of the buffer layer close to the film-substrate interface, In the epilayers also a region of enhanced emission is observed which is partially caused by Si doping and in which structural defects are involved. Cross-sectional CL appears as a useful method to reveal features of the spatial distribution of luminescence, not detectable by plan-view measurements

Cross-sectional cathodoluminescence of GaN epitaxial films

Cathodoluminescence (CL) in the scanning electron microscope has been used to investigate the variation along the growth axis direction of luminescence emission from epitaxial GaN films. CL spectra recorded at different positions of the sample cross-section as well as monochromatic CL images show strong spatial variations of the different luminescence emissions along the growth axis. At the buffer layer-substrate interface and at the top part of the sample, which corresponds to a Si doped epilayer, enhanced CL emission is observed as compared with the relatively low emission in the central region of the cross-section. The nature of the defects responsible for the observed CL distribution is discussed

Influence of deformation on the luminescence of GaN epitaxial films

The effect of indentation on the cathodoluminescence (CL) of GaN:Si epitaxial films has been investigated in the scanning electron microscope. Deformation produces changes in the defect structure which are monitored through the changes induced in the cathodoluminescent emission. Besides a general quenching of the luminescence, an increase of the relative intensity of the deep level bands is observed. The effect of different annealing treatments on the CL emission has been investigated

Cathodoluminescence in europium doped KCl crystals

Spectral cathodoluminescence of KCl:EU2+ (0.2% wt) crystals has been measured at different temperatures. In the 80-300 K temperature range the luminescence consists of three main broad emission bands with maxima around 418, 452, and 619nm. Based on photoluminescence studies the 418nm could be associated with the 4f(6)5d (t(2g))-4f(7) (S-8(7/2)) radiative transition of the Eu2+ ions in the KCl matrix. The band with maximum at 452 nm could be associated with the alpha-center emission as in pure KCl. The 619 nm band has been considered as a part of the luminescence modified by the absorption of the F centers formed during irradiation. The intensity of all these bands versus temperature shows a minimum around 150 K, an indication of a low defect mobility produced with the electron-beam irradiation