The adduct reaction paths for GaN growth by metal organic chemical vapor deposition (MOCVD) were studied by quantum chemical calculations employing density functional theory (DFT). Five possible adduct reaction paths ...The adduct reaction paths for GaN growth by metal organic chemical vapor deposition (MOCVD) were studied by quantum chemical calculations employing density functional theory (DFT). Five possible adduct reaction paths with or without the ex-cess NH3were proposed and the corresponding potential energy surfaces were calculated. From the calculation results, it is concluded that after the formation of DMGNH2from TMG:NH3, the further decomposition paths have very slim probability because of the high energy barriers; whereas the oligomerization pathway to form oligomers [DMGNH2]x(x=2, 3) is probable,because of zero energy barrier. Since the oligomers tend to further polymerize, the nanoparticles are easily formed through this path. When NH3is in excess, TMG:NH3 tends to combine with the second NH3to form two new complexes: the coordination-bonded compound H3N:TMG:NH3and the hydrogen-bonded compound TMG:NH3 NH3. The formation of hydrogen-bonded compound TMG:NH3 NH3 will be more probable because of the lower energy than H3N:TMG:NH3. By comparing the potential energy surfaces in five adduct reaction paths, we postulate that, under the growth conditions of GaN MOCVD, the formation of hydrogen-bonded compound TMG:NH3 NH3 followed by the reversible decomposition may be the main reaction path for GaN thin film growth; while the adduct oligomerization path to generate oligomers [DMGNH2]2 and [DMGNH2]3might be the main reaction path for nanoparticles formation.展开更多
文摘利用低压金属有机化学气相淀积(LP MOCVD)在Si基片上外延生长ZnO薄膜,制备了两类样品一类是在Si上直接外延ZnO,另一类是在Si上通过SiC过渡层来外延ZnO.根据两类样品的拉曼光谱、x射线衍射、原子力显微图和光致发光的结果,表明ZnO外延薄膜中的张应力对薄膜的结晶状况有着重要的影响,使用SiC过渡层能够有效缓解ZnO薄膜中的张应力,减小缺陷浓度,提高ZnO外延层的质量;然后根据缺陷的形成机制进一步提出,对于ZnO Si,其中较大的张应力导致了高浓度的非辐射复合缺陷的形成,使得样品的紫外和绿峰的发射强度均大大降低;对于ZnO SiC Si,其中较小的张应力导致ZnO薄膜中主要形成氧替位缺陷OZn,从而使发光中的绿峰增强.
基金supported by the National Natural Science Foundation of China (Grant No. 61176009)
文摘The adduct reaction paths for GaN growth by metal organic chemical vapor deposition (MOCVD) were studied by quantum chemical calculations employing density functional theory (DFT). Five possible adduct reaction paths with or without the ex-cess NH3were proposed and the corresponding potential energy surfaces were calculated. From the calculation results, it is concluded that after the formation of DMGNH2from TMG:NH3, the further decomposition paths have very slim probability because of the high energy barriers; whereas the oligomerization pathway to form oligomers [DMGNH2]x(x=2, 3) is probable,because of zero energy barrier. Since the oligomers tend to further polymerize, the nanoparticles are easily formed through this path. When NH3is in excess, TMG:NH3 tends to combine with the second NH3to form two new complexes: the coordination-bonded compound H3N:TMG:NH3and the hydrogen-bonded compound TMG:NH3 NH3. The formation of hydrogen-bonded compound TMG:NH3 NH3 will be more probable because of the lower energy than H3N:TMG:NH3. By comparing the potential energy surfaces in five adduct reaction paths, we postulate that, under the growth conditions of GaN MOCVD, the formation of hydrogen-bonded compound TMG:NH3 NH3 followed by the reversible decomposition may be the main reaction path for GaN thin film growth; while the adduct oligomerization path to generate oligomers [DMGNH2]2 and [DMGNH2]3might be the main reaction path for nanoparticles formation.
