Elsevier

Applied Surface Science

Volume 252, Issue 19, 30 July 2006, Pages 7228-7231
Applied Surface Science

SIMS quantification of matrix and impurity species in AlxGa1−xN

https://doi.org/10.1016/j.apsusc.2006.02.148Get rights and content

Abstract

The quantification in AlxGa1−xN with different AlN mole fraction (x) is challenging because of matrix effects and charging effects. For quantitative characterization of both matrix and impurity elements in AlxGa1−xN, a novel charge neutralization method was employed and calibration curves were created using an O2+ primary beam with positive secondary ion detection and a Cs+ primary beam with negative and MCs+ secondary ion detection. Over the range of 0 < x < 0.58, the matrix ion intensity ratios of Al+/Ga+ and AlCs+/GaCs+ appear linear with the mole fraction ratio x/(1  x), and the ratio of AlN/GaN is linear with AlN mole fraction (x). The sputter rate decreases as AlN mole fraction increases, while the relative sensitivity factors (RSF's) of impurities have an exponential relationship with AlN mole fraction. These calibration curves allow the quantification of both matrix and impurity species in AlGaN with varying AlN mole fraction. The technique can be employed for impurity control, composition and growth rate determination, as well as structural analysis of the finished optoelectronic and electronic devices.

Introduction

New applications in optoelectronic devices and high power electronic devices continue to be developed using AlxGa1−xN. Due to the material's wide band gap range, the AlxGa1−xN's are very attractive materials for applications in ultraviolet (UV) laser diodes (LD's), light emitting diodes (LED's) and photo detectors [1]. The large band gap, large electric field breakdown and good thermal/chemical stability make AlxGa1−xN semiconductors the materials of choice for high power, high temperature electronic devices [2].

The properties of AlxGa1−xN materials are strongly influenced by alloy concentration and impurities such as Si, Mg, O, C, H, etc. Thus quantification of matrix and impurity species in AlxGa1−xN is essential for compositional analysis, dopant control, and impurity control. Dynamic SIMS is commonly used for the quantification of AlxGa1−xN due to its capability of providing in-depth profiles with high sensitivity and good depth resolution. However, quantification in AlxGa1−xN can be challenging because of matrix and charging effects. The secondary ion yields of matrix and impurity species vary in AlxGa1−xN with different AlN mole fraction. Sample charging which increases with AlN mole fraction must also be dealt with, particularly in the case of undoped AlxGa1−xN alloys having x > 0.4 [3]. In this work, a SIMS quantification method is developed for the AlxGa1−xN system over the range of x = 0 to 1.

Section snippets

Experiment

A set of AlxGa1−xN films with x ranging from 0 to 0.58 were grown using metal organic chemical vapor deposition (MOCVD). The AlN mole fraction of the AlxGa1−xN films was determined using Low Energy X-Ray Emission Spectroscopy (LEXES). These films were implanted with 24Mg at 120 keV to a dose of 2E14 at./cm2 and 29Si at 150 keV to a dose of 5E14 at./cm2. In order to extend the sample set to include an AlN mole fraction close to but not equal to 1, an AlN sample was implanted with 150 keV 1E17 at./cm2

Sputter rate

Sputter rates normalized to primary ion intensity obtained for the SIMS analytical conditions described above for the AlxGa1−xN samples are presented in Fig. 1. The sputter rates decrease with increasing AlN mole fraction x, which is similar to the result previously reported for AlxGa1−xAs [6]. Although the increase in the Cs+ sputter rate for the 5.5 keV (10 kV primary ion/4.5 kV sample bias) versus the 14.5 keV impact energy (10 kV primary ion/−4.5 kV sample bias) may appear counter intuitive, the

Summary

Using the sputtering conditions presented in this study, the sputter rate decreases with x in AlxGa1−xN. In the range of 0 < x < 0.58, the matrix ion intensity ratios appear to increase linearly with matrix mole fraction or mole fraction ratio. When plotted inversely, the linear correlation appears to increase to 0.39 < x < 1. The overlap of these linear ranges allows quantification of matrix elements over the entire range of AlxGa1−xN's (0 < x < 1) under these analytical conditions.

The RSF's for Si and Mg

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