Combined transmission electron microscopy and cathodoluminescence studies of degradation in electron-beam-pumped Zn1−xCdxSe/ZnSe blue-green lasers

Abstract

We explored degradation in electron-beam-pumped Zn1−xCdxSe/ZnSe laser structures by combining cathodoluminescence (CL) measurements in a scanning electron microscope with transmission electron microscopy. The rate of degradation, measured as the decrease of the emitted CL intensity under electron bombardment, depends critically on the threading dislocation density and on the strain in the quantum well. Degradation occurs via the formation of dark spot defects, which are related to bombardment-induced networks of dislocation loops in the quantum well. These degradation defects often initiate where threading dislocations cross the quantum well. We propose a self-supporting dislocation climb mechanism activated by nonradiative recombination to explain the formation and propagation of the degradation defects.

Evolution of the cathodoluminescence spectral shape and intensity of GaN quantum dots under 10 keV electron beam irradiation

“…The saturation of non-radiative recombination (NR) centers at large J values can explain these trends [7,14]. Thus, NR recombinations are thought to promote the degradation of the CL signal by enhancing the diffusion of point defects which can agglomerate to form dislocation loops similarly to what has been shown to occur in other semiconductors [15][16][17][18]. When J is lower than 1.5 A/cm 2 , NR recombination dominates, leading to a fast degradation of the luminescence, and to the appearance of a dark spot (Fig.…”

Degradation of III‐nitride laser diodes grown by molecular beam epitaxy

“…Such a mechanism would require that a-type dislocations can be mobile in GaN-based materials at room temperature and there is evidence that this is the case: Maeda et al have shown that dislocations with a Burgers vector of a-type exhibited glide motion on the (0001) basal plane and a {1 10 } n pyramidal plane at room temperature under the influence of the electron beam used for TEM observation in crushed GaN powders [5] and in-situ carrier injection experiments by Tomiya et al also showed that dislocation half loops with a-type Burgers vector glided under the electron beam current density of 10 2 Acm -2 [6]. It has been demonstrated that in GaAs-based or ZnSe-based lasers, dislocation loops in the active region could climb due to recombination enhanced defect reaction (REDR) between point defects and dislocations [7,8]. Hence, the dislocation network present in LD2 may result from a similar mechanism of dislocation motion from preexisting defects enhanced by electron-hole recombination, although it is noted that the origin of the dislocation half loops is hard to explain.…”

In-Situ Analysis of Optoelectronic Properties of Semiconductor Nanostructures and Defects in Transmission Electron Microscopes

“…When there is a microstructure, such as a defect, in which the cross section for radiative or non-radiative recombination differs from that in the surrounding homogeneous material, contrast arises in CL images. For example, the spatial distribution of defects in degraded devices (e.g., Sieber et al, 1993, Cheng et al, 1995, Bonard et al, 1998 have been determined. CL contrast due to a defect varies depending on the atomistic structure, size and location of the defect.…”