Because of a large
lattice mismatch between a
sapphire substrate and a group III-V
compound semiconductor, a good
crystal is difficult to grow. A high-quality AlN buffer growth structure A on a
sapphire substrate includes a
sapphire (0001) substrate 1, an AlN
nucleation layer 3 formed on the
sapphire substrate 1, a pulsed supplied AlN layer 5 formed on the AlN
nucleation layer 3, and a continuous growth AlN layer 7 formed on the pulsed supplied AlN layer 5. Formed on the continuous growth AlN layer 7 is at least one set of a pulsed supplied AlN layer 11 and a continuous growth AlN layer 15. The AlN layer 3 is grown in an initial
nucleation mode which is a first growth mode by using an NH3 pulsed supply method. The pulsed supplied AlN layer 5 is formed by using NH3 pulsed supply in a low growth mode which is a second growth mode that increases a grain size and reduces dislocations and therefore is capable of reducing dislocations and burying the nucleation layer 3. The continuous growth AlN layer 7 is a fast
vertical growth mode that improves flatness and suppresses crack occurrences. As examples of the thickness of
layers; the pulsed supplied AlN layer 5, 11 is 0.3 μm and the thickness of the continuous growth AlN layer 7, 15 is 1 μm, for example. Characteristics of conditions under which
layers are grown are as follows. The AlN layer 3 is grown under a high temperature and a
high pressure with a low V-III ratio (less N). The pulsed supplied AlN layer 5 is grown at a low temperature and a low pressure with a high V-III ratio (more N). The continuous AlN layer 7 is grown at a high temperature and a
high pressure with a high V-III ratio (Al rich and less N) without using an NH3 pulsed supply AlN growth method.