We have studied crystal structure and associated defects in GaN films grown on sapphire under nitrogen-deficient conditions by metalorganic chemical vapor deposition (MOCVD) and pulsed laser doposition (PLD). The structural quality of the PLD films grown at 750 degree was comparable with those grown by MOCVD at 1050 degree having threading dislocations density of about 10 sup 10 cm sup -2 at a film hickness 150-200 nm. Microstructure of the PLD films grown at temperatures above 780 degree was found to be similar to that of nitrogen-deficient MOCVD films indicating the loss of nitrogen due to thermal decomposition of the nitride layers. Nitrogen-deficient MOCVD and PLD films exhibit polyerystalline structure with a mixture of cubic zinc-blende and wurtzite hexagonal GaN grains retaining tetragonal bonding actoss the boundaries and hence the epitaxial orientations and polarity. Renucleation of the wurtzite phase at different {111} planes of cubic GaN results in a rough and faceted surface of the film. Most of the stoichiometric films displayed (0001) Ga-face polarity, but the renucleated inclined wurtzite grains grew in the oposite N-face polarity. The major defects related to the dubic structural metastability are stacking faults and microtwins which being nuclei of the metastable cubic phase have an extremely low energy. We elucidate that the cubic phase is more stable under the nitrogen deficiency and, therefore, can exist without decomposition at higher nitrogen vacancy concentrations in the material.
展开▼
机译：我们已经通过金属有机化学气相沉积（MOCVD）和脉冲激光沉积（PLD）研究了在氮缺乏条件下在蓝宝石上生长的GaN膜中的晶体结构和相关的缺陷。在750度下生长的PLD膜的结构质量与在1050度下通过MOCVD在150-200 nm膜厚处具有约10 sup 10 cm sup -2的线位错密度的薄膜的结构质量相当。发现在高于780度的温度下生长的PLD膜的微观结构与缺氮的MOCVD膜的微观结构相似，这表明由于氮化物层的热分解而损失了氮。缺氮的MOCVD和PLD膜表现出多晶结构，立方六面体闪锌矿和纤锌矿型六方GaN晶粒的混合物保留了四方键合，从而限制了边界，从而影响了外延取向和极性。纤锌矿相在立方GaN的不同{111}平面上重新成核，导致薄膜表面粗糙且刻面。大多数化学计量膜显示（0001）Ga面极性，但重新成核的倾斜纤锌矿晶粒以相反的N面极性生长。与二元结构亚稳有关的主要缺陷是堆垛层错和作为亚稳立方相核的微孪晶具有极低的能量。我们阐明了立方相在氮缺乏时更稳定，因此在较高的氮空位浓度下可以存在而不会分解。
展开▼
