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The purpose of this study is to investigate the influence of AlN nucleation thickness in reducing the threading dislocations density in AlN layer grown on sapphire substrate.

In this work, the effect of the nucleation thickness at 5 nm, 10 nm and 20 nm on reducing the dislocation density in the overgrown AlN layer by metal organic chemical vapor deposition was discussed. The AlN layer without the nucleation layer was also included in this study for comparison.

By inserting the 10 nm thick nucleation layer, the density of the dislocation in the AlN layer can be as low as 9.0 × 10⁸ cm⁻². The surface of the AlN layer with that nucleation layer was smoother than its counterparts.

This manuscript discussed the influence of nucleation thickness and its possible mechanism in reducing dislocations density in the AlN layer on sapphire. The authors believe that the finding will be of interest to the readers of this journal, in particular those who are working on the area of AlN.

This study aims to focus on roughening N-face (backside) GaN substrate prior to GaN-on-GaN light-emitting diode (LED) growth as an attempt to improve the LED performance.

The N-face of GaN substrate was roughened by three different etchants; ammonium hydroxide (NH4OH), a mixture of NH₄OH and H₂O₂ (NH₄OH: H₂O₂) and potassium hydroxide (KOH). Hexagonal pyramids were successfully formed on the surface when the substrate was subjected to the etching in all cases.

Under 30 min of etching, the highest density of pyramids was obtained by NH4OH: H₂O₂ etching, which was 5 × 10⁹ cm^–2. The density by KOH and NH₄OH etchings was 3.6 × 10⁹ and 5 × 10⁸ cm^–2, respectively. At standard operation of current density at 20 A/cm², the optical power and external quantum efficiency of the LED on the roughened GaN substrate by NH₄OH: H₂O₂ were 12.3 mW and 22%, respectively, which are higher than its counterparts.

This study demonstrated NH₄OH: H₂O₂ is a new etchant for roughening the N-face GaN substrate. The results showed that such etchant increased the density of the pyramids on the N-face GaN substrate, which subsequently resulted in higher optical power and external quantum efficiency to the LED as compared to KOH and NH₄OH.

To design and optimize the traditional aluminum gallium nitride/gallium nitride high electron mobility transistor (HEMT) device in achieving improved performance and current handling capability using the Synopsys’ Sentaurus TCAD tool.

Varying material and physical considerations, specifically investigating the effects of graded barriers, spacer interlayer, material selection for the channel, as well as study of the effects in the physical dimensions of the HEMT, have been extensively carried out.

Critical figure-of-merits, specifically the DC characteristics, 2DEG concentrations and mobility of the heterostructure device, have been evaluated. Significant observations include enhancement of maximum current density by 63 per cent, whereas the electron concentration was found to propagate by 1,020 cm⁻³ in the channel.

This work aims to provide tactical optimization to traditional heterostructure field effect transistors, rendering its application as power amplifiers, Monolithic Microwave Integrated Circuit (MMICs) and Radar, which requires low noise performance and very high radio frequency design operations.

Analysis in covering the breadth and complexity of heterostructure devices has been carefully executed through extensive TCAD modeling, and the end structure obtained has been optimized to provide best performance.