We have studied the effect of a low-temperature-deposited (LT-) AlGaN interlayer on AlGaN/GaN heterostructure. High-crystalline-quality and crack-free AlGaN layers covering the entire compositional range were realized using the LT-AIN interlayer. We also showed that AlGaN is applicable as the LT-interlayer under the condition that the AlN molar fraction of the LT-AlGaN interlayer is equal to or larger than that of the overgrown,AlGaN layer. Furthermore, electrically conductive LT-Al0.1Ga0.9N has been realized with an intermediate deposition temperature and very high SiH4 flow rate, in addition to the high-quality overgrown AlGaN layer, It is thought that the LT-interlayer technology call overcome the challenges of glowing a high-quality AlGaN layer with high AlN mole fraction on GaN layers.