Nanoscale cathodoluminescene imaging of III‐nitride‐based LEDs with semipolar quantum wells in a scanning transmission electron microscope

Abstract

The optical and crystalline properties of a c‐plane GaN‐based LED structure with embedded semipolar InGaN quantum wells (QW) were investigated using highly spatially resolved cathodoluminescence spectroscopy (CL) directly performed in a scanning transmission electron microscope (STEM). Direct correlation of the cross‐sectional STEM image with the simultaneously recorded spatially resolved CL mapping at room‐temperature reveals the most intense emission coming from the semipolar InGaN QWs. We observe an inhomogeneous wavelength distribution due to local indium fluctuations and varying QW thickness. In contrast, the donor‐acceptor pair recombination (DAP) becomes the dominating luminescence process at 16 K resulting in a superposition of the DAP luminescence and the InGaN QW emission.

Photon bunching reveals single-electron cathodoluminescence excitation efficiency in InGaN quantum wells

“…In CL, a high-energy electron beam in a scanning electron microscope (SEM) excites a material and generates luminescence that is collected and analyzed. CL emission gives valuable spatially resolved information about the band gap [7,8], carrier generation [9], defects [10,11], diffusion and carrier transport [12][13][14], recombination [15,16], and other optoelectronic properties of semiconductors that are used, e.g., in light-emitting diodes (LEDs) [17,18], lasers [19], solar cells [20], and more.…”

Nanoscopic Insights into InGaN/GaN Core–Shell Nanorods: Structure, Composition, and Luminescence

“…The generated CL is collected by a parabolically shaped aluminum mirror located above the sample, coupled into a grating monochromator MonoCL4 (Gatan), and is detected by a liquid N 2 cooled Si charge-coupled device. For STEM–CL measurements, the sample was prepared in cross-section using a conventional mechanical wedge-polishing technique combined with Ar + ion milling in a Gatan PIPS2 ion polishing system, as reported in our previous work . To avoid surface damage of the TEM sample and the formation of amorphous layers, the acceleration voltage and the angle of incidence ranged from 3–5 kV and 4–6°, respectively.…”

“…For STEM−CL measurements, the sample was prepared in cross-section using a conventional mechanical wedge-polishing technique combined with Ar + ion milling in a Gatan PIPS2 ion polishing system, as reported in our previous work. 20 To avoid surface damage of the TEM sample and the formation of amorphous layers, the acceleration voltage and the angle of incidence ranged from 3− 5 kV and 4−6°, respectively. The lamella was thinned to a thickness of about 200 nm to obtain an optimum ratio of electron transparency for high resolution and CL intensity.…”