Development and Application of Electron Beam Induced Current and Cathodoluminescence Analytical Techniques for Characterization of Gallium Nitride-based Devices

by Bunker, Kristin Lee

Abstract (Summary)
The focus of this research was the design, development, and implementation of Electron Beam Induced Current (EBIC) and Cathodoluminescence (CL) techniques on both a Scanning Electron Microscope (SEM) and high-resolution versions on a Scanning Transmission Electron Microscope (STEM). The EBIC and CL techniques were used to characterize electrical and optical properties of fully processed gallium nitride (GaN)-based and indium gallium nitride (InGaN)-based light emitting diodes (LEDs).

SEM-EBIC experiments in a linescan configuration were used to determine the minority carrier diffusion lengths of electrons and holes in a fully processed GaN-based LED. A theoretical model with an extended generation source and a nonzero surface recombination velocity was used to extract the minority carrier diffusion length of the p-type and n-type layers. A minority carrier diffusion length of Ln=(80 ± 6) nm for electrons in the p-type GaN layer, Lp=(70 ± 4) nm for holes in the n-type GaN: Si, Zn active layer, and Ln=(54 ± 4) nm for electrons in the p-type Al0.1Ga0.9N layer were determined.

The STEM-EBIC technique in a linescan configuration was used to determine the p-n junction location of an InGaN-based single quantum well LED with respect to the thin quantum well with nanometer precision. A novel sample preparation method using a Focused Ion Beam (FIB) technique and a custom STEM-EBIC sample holder were designed for these experiments. The relative position of the p-n junction with respect to the InxGa1-xN quantum well was found to be 19 ± 3 nm from the center of the InxGa1-xN quantum well. In addition, the simultaneous acquisition of Z-contrast, EBIC, and elemental aluminum and indium linescans was demonstrated.

Following successful implementation of the STEM-EBIC technique, several advancements to the technique were implemented. A novel sample preparation method was developed involving a variation of the tripod wedge method in combination with the FIB technique to analyze any type of packaged or unpackaged optoelectronic device. The sample preparation is divided into several steps, including mechanical thinning, grid and wire attachment, and FIB milling to create an electron transparent membrane. In addition, a custom cross-sectional STEM-EBIC sample holder was designed to hold the fully prepared optoelectronic devices and allow for simultaneous STEM-EBIC experiments.

A SEM-CL system with polychromatic spectroscopic and panchromatic imaging capabilities was designed and used to examine piezoelectric fields and indium composition fluctuations in an InGaN-based multiple quantum well (MQW) LEDs. The existence and direction of a piezoelectric field was determined with SEM-CL voltage dependence experiments and the magnitude was estimated to be 1.0 ± 0.2 MV/cm. Planar panchromatic CL imaging revealed inhomogeneous intensity on the same LED and spectral CL measurements were used to locally probe the intensity differences and identify any bandgap or indium composition differences.

Finally, a STEM-CL system with polychromatic spectroscopic and panchromatic imaging capabilities was designed, constructed, installed and tested. The STEM-CL design consisted of a lens and fiber optic light collection system and a fiber optic vacuum feedthrough to direct the signal out of the microscope. The technique was demonstrated and STEM-CL spectra were obtained from InGaN-based MQW LEDs.

Bibliographical Information:

Advisor:Dr. Phillip E. Russell; Dr. Gerd Duscher; Dr. Carlton M. Osburn; Dr. Dieter Griffis

School:North Carolina State University

School Location:USA - North Carolina

Source Type:Master's Thesis

Keywords:materials science and engineering


Date of Publication:11/29/2004

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