Quantitative analysis of A l N / S i C interfaces in A l G a N / G a N heterostructures grown on S i C

Abstract

Wide band gap semiconductors, such as SiC and GaN, exhibit many attractive properties: a unique combination of the wide band gap, high breakdown field, high saturation velocity and the ability to form high quality AlGaN/GaN heterostructures with good transport properties make them ideal candidates for high power and high frequency applications. Hexagonal silicon carbide materials (SiC) are considered to be promising candidates for electronic devices as the third generation key materials for transistors. A typical example of a high performance device is the Al x Ga 1‐x N/GaN heterostructure used as a high electron mobility transistor (HEMT) [1‐2]. As 6‐inch SiC wafers are being introduced into the market, a decrease of the substrate off‐cut for SiC heteroepitaxy is desirable to reduce the manufacturing costs [3‐4]. Therefore, multilayer (5 layers) and multicomponent structures (based on GaN and related materials) were grown on 6H‐SiC (with a misorientation of 1 deg. off from the (0001) plane) substrates using the MOVPE method, for high power applications. The layers were grown epitaxially, as it was confirmed from the corresponding electron diffraction patterns. Several types of interfaces were observed between the layers that either ran parallel to the interface or formed V‐shaped defects (e.g. the SiC/AlN, GaN/AlN, GaN/AlGaN interfaces etc.). Moreover, High Resolution TEM (HRTEM) images showed the existence of steps in the 6H‐SiC/AlN interface. A typical HRTEM image where an atomic scale step is observed is shown in Fig. 1. In this study, quantitative analysis of the 6H‐SiC/AlN interface is presented based on experimental HRTEM micrographs, showing and proving the steps sites, the layers' sequence and any strain relaxation situation existing. A structural model based on this analysis is proposed and simulated HRTEM images are also obtained. The corresponding atomic models proposed are found to describe well the 6H‐SiC/AlN interface, with the corresponding computer simulation images coinciding with the experimental HRTEM images. An example is shown in Fig. 2, illustrating the monolayer step observed in the 6H‐SiC/AlN interface. In Fig. 3, a characteristic plot shows the phase shift of the fitting of the intensity's distribution along a line that corresponds to the projection of a close‐packing layer revealing the stacking sequence and therefore the starting position of the AlN epilayer. Moreover, the comparison of the sequence clearly shows the height of the step and any alteration on the stacking sequence between the two parts of the image. Finally, the computer simulated image, as shown in Fig. 4, coincides well with the HRTEM image shown in Fig. 1.