Approaches for optimizing III-N based devices

Three-nitride (III-N) materials have been widely introduced into our everyday lives. Indium gallium nitride (InGaN) light emitting diodes (LEDs) are the backbone of modern lighting sources, while high-mobility electron transistors (HEMTs) based on aluminium gallium nitride (AlGaN) are widely used for high-power high-frequency applications, and GaN power-amplifier devices in 5G technology. However, despite technological and manufacturing advances, devices based on III-N suffer from numerous problems at all stages of their production; beginning with the choice of substrate, continuing with the device design stage and ending with the metallization and characterization stages. There is clearly much room for  making improvements at all stages of the fabrication process. This dissertation presents several approaches for fabrication and design optimization that could improve III-N based devices. GaN epitaxy on patterned 6-inch silicon (Si) substrates was studied. It was shown that thicker layers can be obtained compared to a planar Si substrate. The spatial distribution of the strain in the grown GaN patterns was mapped out using confocal Raman spectroscopy. The studies helped to highlight the shape and size of the cracks in the films. It was also observed that the shape of the corners of the patterned unit affected the uniformity of the strain distribution. With various growth parameters, a 500 × 500 µm2 crack-free area for a 1.5 µm thick GaN film was achieved. In addition to that, the AlN transition layer grown by atomic layer deposition (ALD) was studied as an alternative approach to overcome direct growth issues between GaN and Si substrates. It was shown that AlN ALD layers could be used as a template for further overgrowth. The drawbacks of the conventional current injection principle and the recent progress in novel diffusion-driven current transport (DDCT) design were reviewed. The next generation of such DDCT based devices require the use of selective area growth (SAG), which was implemented and optimized to fabricate lateral heterojunction LED structures. Thus, a finger structure with 2 µm distance between the n- and p-GaN regions was achieved. Besides that, the effect of the geometric dimensions of the fingers on injection efficiency were studied on fabricated back-contacted LED structures with finger widths between 1-20 µm. Finally, the SAG method was also implemented to fabricate heavily doped n+-GaN layers to use them as non-alloyed ohmic contacts.