Substrate effects on the strain relaxation in GaN/AlN short-period superlattices

Abstract

We present a comparative study of the strain relaxation of GaN/AlN short-period superlattices (SLs) grown on two different III-nitride substrates introducing different amounts of compensating strain into the films. We grow by plasma-assisted molecular beam epitaxy (0001)-oriented SLs on a GaN buffer deposited on GaN(thick)-on-sapphire template and on AlN(thin)-on-sapphire template. The ex-situ analysis of strain, crack formation, dislocation density, and microstructure of the SL layers has established that the mechanism of strain relaxation in these structures depends on the residual strain in substrate and is determined mainly by the lattice mismatch between layers. For growth on the AlN film, the compensating strain introduced by this film on the layer prevented cracking; however, the densities of surface pits and dislocations were increased as compared with growth on the GaN template. Three-dimensional growth of the GaN cap layer in samples with pseudomorphly grown SLs on the AlN template is observed. At the same time, two-dimensional step-flow growth of the cap layer was observed for structures with non-pseudomorphly grown SLs on the GaN template with a significant density of large cracks appearing on the surface. The growth mode of the GaN cap layer is predefined by relaxation degree of top SL layers.

Novel attributes of AlGaN/AlN/GaN/SiC HEMTs with the multiple indented channel

“…However, the drain on the proposed structure of the metal occurs as a result of the reduced electric field strength at the edge of the gate and the drain. Considering the above points, the distance between the gate and recessed metal key parameter in determining the breakdown voltage of the HEMT is improved [24][25][26][27][28]. Apart from it, the breakdown voltage is also influenced by the width of the recessed Table 2.…”

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

“…This behavior in the SL period can be explained from determination of average parameters. Average lattice parameters in the SL period were calculated from the equations (1)- (6). From these equations, one can see that those SL periods are strongly dependent on the thickness ratio well-barrier and on barrier composition.…”

“…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].…”

Modeling of X-ray rocking curves for layers after two-stage ion-implantation

“…For ion-modified layers, the structural changes can be qualitatively investigated by analyzing the X-ray diffraction curves in the Bragg geometry. In addition, simulation of X-ray diffraction curves can be used for the depth profiles of strain determination [7][8][9]. However, for the ion-modified structures, simulation of XRD spectra is a difficult task with ambiguous solutions [10][11][12].…”