Structural Characterization of Movpe Grown Algan/Gan for Hemt Formation

Abstract

Results on structural, compositional, optical and electrical characterization of MOVPE grown AlGaN/GaN heterostructures with focus on understanding how the AlN buffer synthesis affects the top films are reported. The study demonstrates very good correlation between different methods providing a platform for reliable estimation of crystalline quality of the AlGaN/GaN structures and related to that electrical performance which is found to be significantly affected by threading dislocations (TD): higher TD density reduces the electron mobility while the charge carrier concentration is found to be largely unchanged. The attempt to vary the ammonia flow during the AlN synthesis is found not to affect the film composition and dislocation densities in the following heterostructures. An unusual phenomenon of considerable diffusion of Ga from the GaN film into the AlN buffer is found in all samples under the study. The obtained results are an important step in optimization of AlGaN/GaN growth towards the formation of good quality HEMT structures on sapphire and transfer of technology to Si substrates by providing clear understanding of the role of synthesis parameter on structure and composition of the films.

Two-dimensional electron gas at the AlGaN/GaN interface: Layer thickness dependence

“…TDs formed in GaN are terminated at the surface as small conical shape pits known as V-defects. 11,25,26 In Fig. 5(c), these defects are visible as black dots.…”

“…Due to the lattice and CTE mismatches, the synthesized GaN films suffer from a high concentration of threading dislocations (TDs), which also affects the crystalline quality of the epitaxial AlGaN layer grown on the top and properties of the 2DEG at the interface. [11][12][13][14] In addition to crystallinity, one needs to consider the composition (Al content x, Al x Ga 1−x N) and layer thickness. Both parameters are found to affect the charge carrier concentration and mobility.…”

Growth of Thin AlN Films on Si Wafers by Reactive Magnetron Sputtering: Role of Processing Pressure, Magnetron Power and Nitrogen/Argon Gas Flow Ratio

“…AlN also has a very high thermal conductivity, which is crucial for heat removal in high-power devices [2]. Currently, AlN films and AlGaN heterostructures are absolutely necessary elements (buffer, transition and capping layers) of high electron mobility transistors and GaN-based diodes [3][4][5]. AlN thin layers are also used in the production of piezoelectric and energy harvesting devices [6,7].…”

Structure and properties of Ta/Al/Ta and Ti/Al/Ti/Au multilayer metal stacks formed as ohmic contacts on n-GaN

“…Growth of GaN epitaxial layers on substrates of other materials (typically, sapphire, SiC and Si) leads to high dislocation densities due to significant lattice mismatches and differences in the coefficients of thermal expansion [7][8][9]. On the one hand, a high defects density limits the advantages of high breakdown field strength in GaN-based power devices.…”