High-Temperature Characteristics of Strain in AlGaN/GaN Heterostructures

The high-temperature characteristics of strain in fully strained and partially strain-relaxed Al 0.2 Ga 0.8 N/GaN heterostructures were investigated at temperatures from room temperature to 800 K by means of the high-resolution X-ray diffraction technique. The results show that an obvious temperature-dependent strain relaxation occurs in both 50-nm- and 100-nm-thick AlGaN layers when the temperature exceeds 523 K. The degree of strain relaxation increases by about 12% and 15% in 50-nm- and 100-nm-thick AlGaN layers, respectively, over the whole temperature range in our measurements. The temperature-dependent strain relaxation results in a theoretical 2DEG reduction of about 5 and 6% for the fully strained and partially strain-relaxed Al 0.22 Ga 0.78 N/GaN heterostructures, respectively. When the temperature is under 523 K, the in-plane strain in the 50-nm-thick AlGaN layer is stabler than that in the 100-nm-thick AlGaN layer due to a lower density of dislocations in the 50-nm-thick AlGaN layer.