Deposition of GaN Layers with a lowered dislocation density by molecular-beam epitaxy

The deposition of a multilayer buffer layer that includes a high-temperature AlN layer grown at a temperature above 1100$^\circ$C has made it possible to reduce the dislocation density in a GaN layer by 1.5–2 orders of magnitude to values in the range from 9 $\times$ 10$^8$ to 1 $\times$ 10$^9$ cm$^{-2}$, compared with the case of growth on a thin low-temperature AlN nucleation layer. The decrease in the dislocation density causes a substantial increase in the electron mobility in the GaN layers to 600–650 cm$^2$ V$^{-1}$ s$^{-1}$, which is in agreement with the results of calculations and is indicative of the high crystalline perfection of the layers.