Kristin Lee Bunker

Minority-carrier diffusion length in a GaN-based light-emitting diode

Minority-carrier diffusion lengths of electrons and holes were measured in a GaN-based light-emitting diode using the electron-beam-induced current technique in the line-scan configuration. A theoretical model with an extended generation source and a nonzero surface recombination velocity was used to accurately extract the diffusion length of the p- 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=(55±4) nm for electrons in the p-type Al0.1Ga0.9N layer were determined. The results from this model are compared with two simpler and widely used theoretical models.

Scanning electron microscopy cathodoluminescence studies of piezoelectric fields in an InGaN∕GaN quantum-well light-emitting diode

Scanning electron microscopy (SEM) cathodoluminescence (CL) experiments were used to determine the existence and direction of piezoelectric fields in a commercial InGaN multiple-quantum-well (MQW) light-emitting diode (LED). The CL emission peak showed a blueshift with increasing reverse bias due to the cancellation of the piezoelectric field. A full compensation of the piezoelectric field was observed followed by a redshift with a further increase of reverse bias, indicating that flat-band conditions had been reached. We determined the piezoelectric field points in the [000-1] direction and estimated the magnitude to be approximately 1MV∕cm. SEM-CL carrier generation density variation and electroluminescence experiments were also used to confirm the existence of a piezoelectric field in the InGaN MQW LED.

Electrical characterization of InGaN quantum well p -n heterostructures

Abstract In this work, two methods for electrical characterization of InGaN quantum well p–n heterostructures at the nanometer level are presented. Cross-sectional Electrical Force Microscopy and High Resolution Electron Beam Induced Current (HR-EBIC) are used to study and identify regions of the cross-sectional surface of InGaN heterostructures with different types of electrical conductivity, the location of the InGaN quantum well, the location of the p–n junction, and the depletion layer. HR-EBIC was implemented in a Scanning Transmission Electron Microscope to take advantage of the high resolution chemical imaging capabilities of this microscope, such as Z-Contrast and Energy Dispersive X-ray Spectroscopy, and the small spread of the high energy electron beam in the electron transparent thin sample that allows electron beam induced current imaging with nanometer resolution.

Focused Ion Beam Sample Preparation of Complex Devices

Focused Ion Beam (FIB) systems can be used for a wide range of demanding sample preparation tasks. The site-specific milling and excellent imaging capabilities of the FIB in combination with the additional features of material deposition, mechanical micromanipulation, gas injection, and selective and chemically enhanced etching of selected materials makes the FIB system an extremely useful and versatile instrument for sample preparation techniques.

Scanning Electron Microscopy Cathodoluminescence Studies of Piezoelectric Fields in an InGaN Multiple Quantum Well Light Emitting Diode

This work involves the development and application of a Scanning Electron Microscopy (SEM)based Cathodoluminescence (CL) system for the investigation of piezoelectric fields in an indium gallium nitride (InGaN)-based optoelectronic device. SEM-based CL experiments in a Hitachi S3200N were used to study the influence of piezoelectric fields on the luminescence properties of a commercial Cree, Inc. InGaN-based MQW X-Bright green Light Emitting Diode [1]. The existence and direction of the piezoelectric field in the InGaN-based device were investigated using SEM-CL peak voltage dependence and carrier generation density (i.e. beam current) dependence studies. Supporting evidence for the existence of a piezoelectric field in the device was determined from forward bias electroluminescence experiments.