Defects and Interfaces in III-Nitride/Sapphire Thin Film Heterostructures

Abstract

AbstractHigh quality III-nitrides and zinc oxide thin film heterostructures have been fabricated using pulsed laser deposition (PLD) on highly lattice mismatched sapphire substrates. The structural quality of PLD films grown at 700-800°C is comparable with those grown by MOCVD in the temperature range 950-1050°C. The PLD films were found to be single crystalline with columnar structure having the dislocation density of ~1010 cm2 at a film thickness 150-200 nm. The typical structure of defects and interfaces in GaN and AIN films is analyzed and compared with those obtained from specimens grown by MOCVD at much higher temperatures. Low temperature PLD (< 780°C) does not require additional atomic nitrogen source to compensate for the loss of nitrogen due to thermal decomposition of the nitride layer. At slightly higher temperatures the GaN films exhibit rough morphology and formation of the cubic zinc-blende phase which is more stable against nitrogen deficiency than wurtzite phase. A mechanism of formation of zinc-blende phase has been identified. Growth of GaN on lattice-matched ZnO/sapphire buffer layers showed the formation of cubic spinel ZnGa2O4 intermediate layer.