The cathodoluminescence contrast formation of localized non-radiative defects in semiconductors

Abstract

The contrast formation of localized non-radiative semiconductor defects in cathodoluminescence (CL) micrographs is analyzed using a linear relationship between the CL intensity and the excess carrier density 8p. The latter is evaluated on the basis of Donolato's Born approximation and for generation by a point source. Numerical calculations for a threading dislocation a t right angle to a surface of infinite recombination velocity yield an exponential decay of the CL contrast a t sufficient distance from the dislocation with a decay constant of 0.63 minority carrier diffusion lengths. The contrast mechanism is seen to be based primarily on the reduction of the total number of excess carriers due to enhanced recombination a t the dislocation rather than on the associated reduction of the luminescence quantum efficiency.Die Kontrastbildung lokalisierter nicht-strahlender Halbleiterdefekte in Kathodolumineszenz (KL)-Mikrobildern wird unter Zugrundelegung einer linearen Beziehung zwischen der KL-Intensitiit und der tfberschuBladungstrigerdichte Sp analysiert. Sp wird auf der Grundlage von Donolatos Bornscher NiCherung und unter der Annahme punktformiger Generation ermittelt. Numerische Berechnungen fur eine Versetzung senkrecht zur Oberfliiche, fur die eine unendliche Oberfliichenrekombinationsgeschwindigkeit zugrunde gelegt wird, ergeben fur genugend grol3e Abstiinde von der Versetzung einen exponentiellen Abfall des KL-Kontrasts mit einer Abfallkonstante von 0,63 Minoritiitstriigerdiffusionsliingen. Es zeigt sich, daD der Kontrastmecbanismus primiir auf der Reduktion der gesamten OberschuDtriigerzehl durch verstiirkte Rekombination an der Versetzung beruht und nicht so sehr auf der damit verbundenen Reduktion der Lumineszenzquantenausbeute.

Theoretical Study on the Effects of Dislocations in Monolithic III-V Lasers on Silicon

“…Since the exact dislocation carrier capture time is not known, we assume here a capture time of the order of a few picoseconds, comparable with the one into QD states [38], [39]. In reality, the physical radius of an actual dislocation core is estimated to be only a few tens of nanometers [40], [41], so varying dis is not only a means of modelling realistic performance trends with growing dislocation density, but also a way to compensate for larger z, which overestimate the dislocation size slightly. For z = 500 nm, a value of dis = 10 ps is chosen to model dislocation sections, whereas dis is set to infinity in dislocation-free regions.…”

SEM‐CL studies of plastic deformation processes in crystals

“…The dislocations may have their own energy levels in the band gap and. respectively, specific lines in the CL spectrum (Lohnert andKubalek 1984, Yacobi andHold 1986). In most cases, the dislocations are nonluniinescent.…”

A note on the spatial resolution of cathodoluminescence images

“…This law applies to the one-dimensional case, whereas in three dimensions p actually decreases as (l/r) exp (-r/L); as a consequence of the geometrical factor l/r, the extent of the cloud of beam-injected minority carriersand hence the resolution of the CL imageremains of the order of Re, even in the limit of L + co [2]. This point has been elucidated in connection with the modeling of the EBIC images of semiconductor defects [2, 31, and is mentioned in related review articles [9 to 111, but apparently its relevance for CL imaging has been overlooked, in spite of the similarity between the contrast formation of the two techniques [12].In this connection, it should be noted that in [l] the diffusion equation (1) as it stands is clearly incorrect; moreover, the claim that this equation has been analytically solved only for the point source or the uniform generation sphere seems to neglect, for instance, the solution given in [13] for generation with a Gaussian lateral distribution having depth -dependent amplitude and variance.…”

“…This law applies to the one-dimensional case, whereas in three dimensions p actually decreases as (l/r) exp (-r/L); as a consequence of the geometrical factor l/r, the extent of the cloud of beam-injected minority carriersand hence the resolution of the CL imageremains of the order of Re, even in the limit of L + co [2]. This point has been elucidated in connection with the modeling of the EBIC images of semiconductor defects [2, 31, and is mentioned in related review articles [9 to 111, but apparently its relevance for CL imaging has been overlooked, in spite of the similarity between the contrast formation of the two techniques [12].…”