Effect of buffer Design on AlN/AlN/GaN Heterostructures by MBE

The effect of the buffer layers on the subsequent GaN epitaxial layers and electrical properties of AlGaN/AIN/GaN heterojunction structures nitrided at various temperatures was investigated. For AIN buffer layers, two different growth conditions of AIN buffer layers were introduced to avoid Al droplets. We found that etch pit density and structural quality of GaN epitaxial layer strongly depends on the growth conditions of AIN buffer layers. When using a double buffer layer (low temperature GaN on high temperature AIN) for 200 degreesC nitridation, the etch pit density was measured to high 107 cm(-2) in GaN epitaxial layers. Furthermore, we observed that electrical properties of AlGaN/AIN/GaN heterostructures depend on growth conditions of buffer layers and nitridation temperatures. The mobility in Al0.33Ga0.67N/AIN/GaN structures grown on single AIN buffer layers for 200 degreesC nitridation were 1300 cm(2)/Vs at a sheet charge of 1.6 x 10(13) cm(-2). Using the double buffer layer for 200 degreesC nitridation, the mobility increased to 1587 cm(2)/Vs with a sheet charge of 1.25 x 10(13) cm(-2).