Crack Statististics and Stress Analysis of Thick GaN on Patterned Silicon Substrate

In this work, crack statistics are developed for MOCVD-grown 12m thick GaN on patterned Si substrate for different sizes, trench widths and trench heights of the mesas. Optical microscope is used to obtain the percentage of cracked mesas in order to develop the crack statistics. The crack statistics show that the size and the trench height of the mesas have large effects on the percentage of cracked mesas but the trench width has no significant effect. The stress on crack-free thick GaN mesas is investigated by micro-Raman scattering process at room temperature by varying the size, trench height and trench width of the mesas. Both crack statistics and stress measurement show the similar behavior while varying these features of the mesas. According to Raman analysis, the critical stress for cracking of 12m GaN films is about 1.8GPa.