Non-destructive determination of ultra-thin GaN cap layer thickness in AlGaN/GaN HEMT structure by angle resolved x-ray photoelectron spectroscopy (ARXPS)

Anshu Goyal,Brajesh S. Yadav,R. Raman,Ashok K. Kapoor

doi:10.1063/1.5011801

Anshu Goyal, Brajesh S. Yadav + Show 2 more

Open Access

https://doi.org/10.1063/1.5011801

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Journal: AIP Advances	Publication Date: Feb 1, 2018
Citations: 6	License type: cc-by

Affiliation: Solid State Physics Laboratory

Abstract

Angle resolved X-ray photoelectron spectroscopy (ARXPS) and secondary ion mass spectrometry (SIMS) investigations have been carried out to characterize the GaN cap layer in AlGaN/GaN HEMT structure. The paper discusses the qualitative (presence or absence of a cap layer) and quantitative (cap layer thickness) characterization of cap layer in HEMT structure non-destructively using ARXPS measurements in conjunction with the theoretical modeling. Further the relative sensitive factor (RSF=σGaσAl) for Ga to Al ratio was estimated to be 0.963 and was used in the quantification of GaN cap layer thickness. Our results show that Al/Ga intensity ratio varies with the emission angle in the presence of GaN cap layer and otherwise remains constant. Also, the modeling of this intensity ratio gives its thickness. The finding of ARXPS was also substantiated by SIMS depth profiling studies.

Highlights

Group–III nitride semiconductors are considered to have large potential in optoelectronic and microelectronic applications.[1,2] This is due to nitrides having properties such as larger band gap, high thermal stability, strong chemical bonds, high mobility of the electrons.[3]
We are reporting the estimation of GaN cap layer thickness in AlGaN/GaN HEMT structure using the angle resolved x-ray photoelectron spectroscopy (ARXPS) technique
The oxygen peak comes from the adsorbed as well as from native oxides formed on the surface, this does not affect the interpretation of data for the cap layer thickness

Summary

INTRODUCTION

Group–III nitride semiconductors are considered to have large potential in optoelectronic and microelectronic applications.[1,2] This is due to nitrides having properties such as larger (direct) band gap, high thermal stability, strong chemical bonds, high mobility of the electrons.[3]. It is important to accurately measure the thickness of ultrathin cap layer in AlGaN/GaN HEMT structure to optimize its device properties for best performance and reliability. In case of GaN/AlGaN layers, where a GaN cap is present on the AlGaN barrier layer, the conventional XPS may not be used for thickness estimation, as the photoelectrons (either Ga or N) originating from both the GaN cap layer and as well as from AlGaN barrier layer are not differentiable on the energy scale as two distinctive peaks, unlike the case of SiO2 film on Si substrate as mentioned by the Seah et al.[10,11] This inherent problem with AlGaN/GaN HEMT heterostructure was attempted for the non-destructive solution with the ARXPS. We are reporting the estimation of GaN cap layer thickness in AlGaN/GaN HEMT structure using the ARXPS technique. We show that the results of the two techniques matches well

EXPERIMENTAL

Qualitative analysis of cap layer by XPS

Simulation of GaN cap thickness using ARXPS

SIMS analysis for cap layer identification

CONCLUSION