supplied into the chamber 324 to form n type gan layer 3 doped with si of 2 u03bcm thickness subsequently tmg of 4 sccm and tma of 2 sccm are supplied thereinto to form n type al 0 1 ga 0 9 n layer 4 doped with si of 0 1 u03bcm thickness thereafter the distance between the heater 323 and the sapphire substrate 1 on the substrate holder 313 is increased vertically by 3 mm from its original distance to decrease the substrate temperature from 1000 u00b0 c to 800 u00b0 c while supplies of tma tmg and sih 4 are stopped subsequently trimethylindium tmi of 100 sccm tmg of 2 sccm and nh 3 of 5 slm are supplied thereinto to form in 01 ga 0 9 n layer 5a of 5 nm thickness thereafter the distance between the heater 323 and the sapphire substrate 1 on the substrate holder 313 is increased vertically by 2 mm to decrease the substrate temperature from 800 u00b0 c to 700 u00b0 c while supply of nh 3 is stopped subsequently tmi of 300 sccm and tmg of 1 sccm are supplied thereinto to form in 0 3 ga 0 7 n layer 6 of 5 nm thickness thereafter the distance between the heater 323 and the sapphire substrate 1 on the substrate holder 313 is decreased vertically by 2 mm to increase the substrate temperature from 700 u00b0 c to 800 u00b0 c subsequently tmi of 100 sccm tmg of 2 sccm and nh 3 of 5 slm are supplied thereinto to form in 0 1 ga 0 9 n layer 5b of 5 nm thickness thereafter the distance between the heater 323 and the sapphire substrate 1 on the.