Elimination of AlGaN epilayer cracking by spatially patterned AlN mask

The inherent problem in III-nitride technology is the cracking of AlGaN layers that results from lattice mismatch between AlGaN and GaN. In case of thin substrates ( 30 - 90 μ m ) , such as, bulk GaN grown by the high-pressure/high-temperature method, the bowing of Al Ga N ∕ Ga N strained structures becomes an additional problem. To eliminate cracking and bowing, AlGaN layers were grown on GaN substrates with an AlN mask patterned to form 3 - 15 μ m wide windows. In the 3 μ m window, the AlGaN layer was not cracked, although its thickness and Al composition exceeded critical values for growth on nonpatterned substrates. Dislocation density in the windows was of 5 × 10 6 ∕ cm 2 .