Quantification of Trace-Level Silicon Doping in Al_xGa_1–xN Films Using Wavelength-Dispersive X-Ray Microanalysis

Abstract

Wavelength-dispersive X-ray (WDX) spectroscopy was used to measure silicon atom concentrations in the range 35–100 ppm [corresponding to (3–9) × 1018 cm−3] in doped Al x Ga1–xN films using an electron probe microanalyser also equipped with a cathodoluminescence (CL) spectrometer. Doping with Si is the usual way to produce the n-type conducting layers that are critical in GaN- and Al x Ga1–xN-based devices such as LEDs and laser diodes. Previously, we have shown excellent agreement for Mg dopant concentrations in p-GaN measured by WDX with values from the more widely used technique of secondary ion mass spectrometry (SIMS). However, a discrepancy between these methods has been reported when quantifying the n-type dopant, silicon. We identify the cause of discrepancy as inherent sample contamination and propose a way to correct this using a calibration relation. This new approach, using a method combining data derived from SIMS measurements on both GaN and Al x Ga1–xN samples, provides the means to measure the Si content in these samples with account taken of variations in the ZAF corrections. This method presents a cost-effective and time-saving way to measure the Si doping and can also benefit from simultaneously measuring other signals, such as CL and electron channeling contrast imaging.

A systematic comparison of polar and semipolar Si-doped AlGaN alloys with high AlN content

“…For estimating the Si concentration, a calibration method was used. The method involves measuring the Si intensity of all samples and comparing with Al x Ga 1-x N and GaN reference samples for which Si concentration was known from secondary ion mass spectrometry (SIMS) analysis [37,38]. Doping densities evaluated by this method are in the of range 10 17 -10 19 cm −3 .…”

“…Doping densities evaluated by this method are in the of range 10 17 -10 19 cm −3 . The concentration determined directly from the WDX are over-estimated, likely as a result of surface contamination [38].…”