Abstract
As an important wide-bandgap semiconductor, gallium nitride (GaN) has attracted considerable attention. This paper describes the use of confocal Raman spectroscopy to characterize undoped GaN, n-type GaN, and p-type GaN through depth profiling using 405-, 532-, and 638-nm wavelength lasers. The Raman signal intensity of the sapphire substrate at different focal depths is studied to analyze the depth resolution. Based on the shift of the E2H mode of the GaN epitaxial layer, the interfacial stress for different types of GaN is characterized and calculated. The results show that the maximum interfacial stress appears approximately at the junction of the GaN and the sapphire substrate. Local interfacial stress analysis between the GaN epitaxial layer and the substrate will be very helpful in furthering the applications of GaN devices.
Highlights
Gallium nitride (GaN) is a third-generation semiconductor material that has a high breakdown electric field, large forbidden bandgap, high thermal conductivity, high electron saturation velocity, and strong radiation resistance
In this paper, undoped, n-type, and p-type GaN materials on a sapphire substrate are characterized with depth profiling through confocal Raman spectroscopy
This peak may be due to the Mg ion doping in the p-type GaN, which increases the number of defects in the sample and enhances the dislocation
Summary
Gallium nitride (GaN) is a third-generation semiconductor material that has a high breakdown electric field, large forbidden bandgap, high thermal conductivity, high electron saturation velocity, and strong radiation resistance. The main problems with GaN heteroepitaxial growth stem from lattice mismatch and thermal stress mismatch of heterogeneous substrates. Scitation.org/journal/npe a large lattice mismatch will cause a high density of dislocations (108–1010 cm-2) in the GaN epitaxial layer. Growing GaN on a substrate with an excessively different coefficient of thermal expansion will produce a large biaxial stress during the cooling process and may cause microcracks, which will degrade the optoelectronic properties of the epitaxial layer.. Interfacial studies on defect characterization, stress analysis, and new buffer layer settings are the key to preparing high-quality GaN epilayers. Through confocal micro-Raman spectroscopy, Kladko et al revealed the epitaxial structure of the nitride layer and the micrometer-scale depth distribution of the deformation gradient in a sapphire substrate interface region.. In this paper, undoped, n-type, and p-type GaN materials on a sapphire substrate are characterized with depth profiling through confocal Raman spectroscopy. The interfacial stress distribution and resolution corresponding to different excitation light wavelengths and different depths are analyzed and discussed
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