Analysis of doping concentration and composition in wide bandgap AlGaN:Si by wavelength dispersive x-ray spectroscopy

Gunnar Kusch,Paul R Edwards,Robert W Martin,Frank Mehnke,Michael Kneissl,Tim Wernicke,Johannes Enslin

doi:10.1088/1361-6641/aa58cf

Abstract

Detailed knowledge of the dopant concentration and composition of wide band gap AlxGa layers is of crucial importance for the fabrication of ultra violet light emitting diodes. This paper demonstrates the capabilities of wavelength dispersive x-ray (WDX) spectroscopy in accurately determining these parameters and compares the results with those from high resolution x-ray diffraction (HR-XRD) and secondary ion mass spectrometry (SIMS). WDX spectroscopy has been carried out on different silicon-doped wide bandgap AlxGa samples (x between 0.80 and 1). This study found a linear increase in the Si concentration with the SiH4/group-III ratio, measuring Si concentrations between cm−3 and cm−3, while no direct correlation between the AlN composition and the Si incorporation ratio was found. Comparison between the composition obtained by WDX and by HR-XRD showed very good agreement in the range investigated, while comparison of the donor concentration between WDX and SIMS found only partial agreement, which we attribute to a number of effects.

Highlights

Wide bandgap group-III nitride semiconductors are of significant current interest due to the numerous possible applications of ultra violet (UV) light emitting devices, including: water purification [1], gas sensing, and medical diagnostics
Technol. 32 (2017) 035020 paper we report on the determination of composition and doping concentration in wide band gap AlxGa1-xN:Si layers using wavelength dispersive x-ray (WDX) spectroscopy in an electron probe microanalyzer (EPMA) and compare the results with: x-ray diffraction (XRD) and secondary ion mass spectrometry (SIMS)
The WDX technique enables a non-destructive determination of the composition of wide bandgap AlxGa1-xN alloys and is in good agreement with XRD measurements, well below the margin of error (2.5%–3% AlN%, see table 2)

Summary

Introduction

Wide bandgap group-III nitride semiconductors are of significant current interest due to the numerous possible applications of ultra violet (UV) light emitting devices, including: water purification [1], gas sensing, and medical diagnostics. 32 (2017) 035020 paper we report on the determination of composition and doping concentration in wide band gap AlxGa1-xN:Si layers using wavelength dispersive x-ray (WDX) spectroscopy in an electron probe microanalyzer (EPMA) and compare the results with: x-ray diffraction (XRD) and secondary ion mass spectrometry (SIMS). XRD measurements are widely used to obtain compositional information of semiconductor structures. This is achieved by measuring the lattice constant of a given layer and requires prior knowledge of the strain state of the semiconductor in order to precisely determine the composition. Unlike SIMS, WDX is non-destructive and can readily be used for quantitative multi-element analysis, allowing determination of the composition and doping concentration at the same time. The calibration standards used for WDX are less costly than the ion-implanted standards required for the calibration of SIMS measurements determining the dopant concentration. The characterization of very thin films is challenging due to the requirement of a minimum electron energy to excite characteristic x-rays, depending on the elements under investigation

Experimental

Comparison of Al composition as determined by WDX and XRD

Determination of the doping concentration by WDX

Summary