Internal strains and crystal structure of the layers in AlGaN/GaN heterostructures grown on a sapphire substrate

Abstract

In this paper, we investigate the structural properties of AlGaN/GaN heterostructures grown by metal organic chemical vapor deposition on sapphire substrates with different thicknesses using high-resolution x-ray diffraction and Raman scattering methods. We discuss the microscopic nature of spatial-inhomogeneous deformations and dislocation density in the structures. Microdeformations within mosaic blocks and the sizes of regions of coherent diffraction are determined. We reveal a gradient depth distribution of deformations in the mosaic structure of nitride layers, as well as at the interface regions of the sapphire substrate on the microscale level using confocal micro-Raman spectroscopy. We determine that an increase in substrate thickness leads to a reduction in dislocation density in the layers and an increase in the elastic deformations. The features of the block structure of nitrides layers are shown to have a significant influence on their elastic properties.

Structural, optical, and transport properties of AlGaN/GaN and AlGaN/InGaN heterostructure on sapphire grown by plasma assisted molecular beam epitaxy

“…42 Of these, A 1 and E 1 are both Raman and infrared active, whereas 2E 2 set ðE low 2 and E high 2 Þ are only Raman active and B 1 mode are optically silent. 12 Additionally, macroscopic electric field splits the polar A 1 and E 1 into longitudinal optical (LO) and transverse optical (TO) phonon modes. So, in the first-order Raman scattering, all of the A 1 ðLOÞ, A 1 ðTOÞ, E 1 ðLOÞ, E 1 ðTOÞ, E low 2 ; and E high 2 can be observed.…”

“…[5][6][7][8][9][10] However, sapphire (Al 2 O 3 ) is used as a substrate for growth of III-N based epitaxial layer in spite of its larger lattice mismatch and larger thermal expansion coefficient by taking diverse growth approaches. 11,12 Notably, in these devices, AlGaN alloys are used as barrier layers, leading to excellent carrier confinement at AlGaN/GaN interface without intentional doping. [13][14][15][16][17] Generally, GaN is used as the channel material for realization of polarization induced sheet carrier concentrations at the corresponding interface.…”

Light-emitting diode quality investigation via low-frequency noise characteristics

“…So, there is huge interest in improving the design of nitride based LEDs and the methods of growth of nitride crystals and layers [4]. Various methods for improving of growth of nitride crystals and for decreasing the number of defects in these materials are looking for by manufacturers: the effect of surfaces and surface preparation, particularly wet and dry etching, exposure to UV light in vacuum or controlled gas ambient, annealing, and ion implantation [2,[4][5][6]. But real improvement in LED performance and reliability needs in-depth understanding the reasons of defect number growth, what leads to the migration of defects during device aging, and how these processes affect the operation characteristics and degradation of LEDs.…”

Deformation state of short-period AlGaN/GaN superlattices at different well-barrier thickness ratios

“…In previous works [3][4][5][6], it was shown that at epitaxial growth of nitride structures they relaxed by formation of dislocations and other defects also by changing of well-barrier thicknesses in SL from technological thicknesses. The deformation state, thickness fluctuation and defects in SL negatively affect on the devices performance changing their wavelength, carrier transport and carrier lifetime [7][8][9].…”