Interlayers Ease Mismatch Stress

Efficient infrared and red vertical-cavity surface-emitting lasers will require high-quality AlGaN/GaN distributed Bragg reflectors, but the lattice mismatch between GaN and AlN leads to the formation of cracks. Now a research team from Sandia National Laboratories in Albuquerque, N.M., and Brown University in Providence, R.I., has demonstrated that inserting AlN interlayers during the growth process reduces mismatch stress.

The researchers deposited 150-Å-thick layers of AlN during the growth of 2-in. wafers of distributed Bragg reflectors. Tests suggest that the interlayers convert tensile stress into compression, doubling the critical thickness for cracking. They reported the results in the May 21 issue of Applied Physics Letters.