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Adatom migration process on different substrate surfaces: (a-d) on (0001) Al-terminated AlN surface and (e-h) on 0001 N-terminated AlN surface with growth temperature of 1450 K and injected Al:Ga = 1:1. The deep blue and light blue atoms represent Al and N atoms in the AlN substrate while the green, red, and yellow atoms represent Al, Ga and N atoms in the deposited film correspondingly.
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The growth of AlGaN has been extensively studied, but corresponding research related to the effect of AlN substrate surface has rarely been reported in literature. In this article, the effects of AlN substrate surface on deposition of AlGaN films were investigated by molecular dynamics (MD) simulations. (0001) Al-terminated and (0001¯) N-terminated...
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Context 1
... further verify the different mobility of Al and Ga adatoms on two different surfaces, the time-resolved processes for migration of adatoms on the substrate surfaces at 1450 K and injected Al:Ga = 1:1 are displayed in Figure 8. Figure 8a-d shows the migration process of adatoms on (0001) Al-terminated AlN surface, while Figure 8e-h shows the migration process of adatoms on 0001N-terminated AlN surface. In Figure 8a,b, the adatoms successively approach the substrate then start to bond with appropriate atoms. We can see in Figure 6c that the N adatom bonds with Al atom on the substrate and another N adatom moves toward the Al adatoms. The next moment, in Figure 8d, the bond between the first N adatom and substrate Al atom breaks up and the N adatom moves toward the Ga adatom to find a new lattice site. Meanwhile, another pair of Al and N adatoms also move towards each other. A similar process can be observed in Figure 8e-h. However, when we carefully compare the migration processes on different surfaces, we find that Al and Ga adatoms gradually move away from their initial position after they approach the (0001) Al-terminated surface. By comparison, Al and Ga adatoms have little movement from their initial position after they approach the 0001 N-terminated surface. Apparently, Al and Ga adatoms have a longer migration length on (0001) Al-terminated AlN surface than on 0001 N-terminated AlN surface, facilitating the movement of Al and Ga adatoms to find the ideal lattice site. ...
Context 2
... further verify the different mobility of Al and Ga adatoms on two different surfaces, the time-resolved processes for migration of adatoms on the substrate surfaces at 1450 K and injected Al:Ga = 1:1 are displayed in Figure 8. Figure 8a-d shows the migration process of adatoms on (0001) Al-terminated AlN surface, while Figure 8e-h shows the migration process of adatoms on 0001N-terminated AlN surface. In Figure 8a,b, the adatoms successively approach the substrate then start to bond with appropriate atoms. We can see in Figure 6c that the N adatom bonds with Al atom on the substrate and another N adatom moves toward the Al adatoms. The next moment, in Figure 8d, the bond between the first N adatom and substrate Al atom breaks up and the N adatom moves toward the Ga adatom to find a new lattice site. Meanwhile, another pair of Al and N adatoms also move towards each other. A similar process can be observed in Figure 8e-h. However, when we carefully compare the migration processes on different surfaces, we find that Al and Ga adatoms gradually move away from their initial position after they approach the (0001) Al-terminated surface. By comparison, Al and Ga adatoms have little movement from their initial position after they approach the 0001 N-terminated surface. Apparently, Al and Ga adatoms have a longer migration length on (0001) Al-terminated AlN surface than on 0001 N-terminated AlN surface, facilitating the movement of Al and Ga adatoms to find the ideal lattice site. ...
Context 3
... further verify the different mobility of Al and Ga adatoms on two different surfaces, the time-resolved processes for migration of adatoms on the substrate surfaces at 1450 K and injected Al:Ga = 1:1 are displayed in Figure 8. Figure 8a-d shows the migration process of adatoms on (0001) Al-terminated AlN surface, while Figure 8e-h shows the migration process of adatoms on 0001N-terminated AlN surface. In Figure 8a,b, the adatoms successively approach the substrate then start to bond with appropriate atoms. We can see in Figure 6c that the N adatom bonds with Al atom on the substrate and another N adatom moves toward the Al adatoms. The next moment, in Figure 8d, the bond between the first N adatom and substrate Al atom breaks up and the N adatom moves toward the Ga adatom to find a new lattice site. Meanwhile, another pair of Al and N adatoms also move towards each other. A similar process can be observed in Figure 8e-h. However, when we carefully compare the migration processes on different surfaces, we find that Al and Ga adatoms gradually move away from their initial position after they approach the (0001) Al-terminated surface. By comparison, Al and Ga adatoms have little movement from their initial position after they approach the 0001 N-terminated surface. Apparently, Al and Ga adatoms have a longer migration length on (0001) Al-terminated AlN surface than on 0001 N-terminated AlN surface, facilitating the movement of Al and Ga adatoms to find the ideal lattice site. ...
Context 4
... further verify the different mobility of Al and Ga adatoms on two different surfaces, the time-resolved processes for migration of adatoms on the substrate surfaces at 1450 K and injected Al:Ga = 1:1 are displayed in Figure 8. Figure 8a-d shows the migration process of adatoms on (0001) Al-terminated AlN surface, while Figure 8e-h shows the migration process of adatoms on 0001N-terminated AlN surface. In Figure 8a,b, the adatoms successively approach the substrate then start to bond with appropriate atoms. We can see in Figure 6c that the N adatom bonds with Al atom on the substrate and another N adatom moves toward the Al adatoms. The next moment, in Figure 8d, the bond between the first N adatom and substrate Al atom breaks up and the N adatom moves toward the Ga adatom to find a new lattice site. Meanwhile, another pair of Al and N adatoms also move towards each other. A similar process can be observed in Figure 8e-h. However, when we carefully compare the migration processes on different surfaces, we find that Al and Ga adatoms gradually move away from their initial position after they approach the (0001) Al-terminated surface. By comparison, Al and Ga adatoms have little movement from their initial position after they approach the 0001 N-terminated surface. Apparently, Al and Ga adatoms have a longer migration length on (0001) Al-terminated AlN surface than on 0001 N-terminated AlN surface, facilitating the movement of Al and Ga adatoms to find the ideal lattice site. ...
Context 5
... further verify the different mobility of Al and Ga adatoms on two different surfaces, the time-resolved processes for migration of adatoms on the substrate surfaces at 1450 K and injected Al:Ga = 1:1 are displayed in Figure 8. Figure 8a-d shows the migration process of adatoms on (0001) Al-terminated AlN surface, while Figure 8e-h shows the migration process of adatoms on 0001N-terminated AlN surface. In Figure 8a,b, the adatoms successively approach the substrate then start to bond with appropriate atoms. We can see in Figure 6c that the N adatom bonds with Al atom on the substrate and another N adatom moves toward the Al adatoms. The next moment, in Figure 8d, the bond between the first N adatom and substrate Al atom breaks up and the N adatom moves toward the Ga adatom to find a new lattice site. Meanwhile, another pair of Al and N adatoms also move towards each other. A similar process can be observed in Figure 8e-h. However, when we carefully compare the migration processes on different surfaces, we find that Al and Ga adatoms gradually move away from their initial position after they approach the (0001) Al-terminated surface. By comparison, Al and Ga adatoms have little movement from their initial position after they approach the 0001 N-terminated surface. Apparently, Al and Ga adatoms have a longer migration length on (0001) Al-terminated AlN surface than on 0001 N-terminated AlN surface, facilitating the movement of Al and Ga adatoms to find the ideal lattice site. ...
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Citations
... Similar SW potentials have already been successfully applied to investigate an InGaN film grown on a GaN surface. [19][20][21] To begin with, an energy minimization of the system by iteratively adjusting atom coordinates was performed. Then the NPT ensemble (constant temperature and constant volume) was used to balance 300 ps at 300 K, and the time step was 1 fs. ...
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... The parameters of Al-Ga-N SW potential are shown in Table 1. More details can be found in references [24,25,30,31]. Table 1. ...
... Table 1. Stillinger-Weber potential parameters for the Al-Ga-N systems [30,31]. ...
... AlN or GaN often serves as the buffer layer for growing AlGaN due to the small lattice mismatch between them [32]. The growth model of AlGaN on AlN was established by referring to the modeling method in reference [30,31]. Dai et al. [33][34][35] developed a numerical model for the stresses and other properties of AlN films grown on a Si(111) substrate. ...
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... Similar study results were obtained by Lundin et al. and Touzi et al. 53,43 Furthermore, Lundin et al. also found that although the Al component decreased with the rise of III-nitride, the rate of decrease in the high ammonia atmosphere was significantly faster than that in the low. In addition, as the ratio of the III-nitride flow rate rose in the total gas, the growth rate also grews, 26,47,49,55,56 thus it was difficult to achieve rapid growth of the AlGaN layer and obtain a high Al component simultaneously by adjusting the III-nitride flow rate. Figure 6 demonstrated the effect of the TMAl/III flow rate ratio on the growth rate of AlGaN. ...
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In this article, we study the deposition of AlGaN film on AlN template by molecular dynamics (MD) simulations. The effects of growth temperature and film thickness on the dislocation of deposited AlGaN film are simulated and studied. The atomic structure of deposited AlGaN film is also investigated. We find that the dislocations usually occur at the interface between AlN template and AlGaN film and then extend towards the growth direction. The dislocation density decreases with the increase of AlGaN film thickness, which indicates that increasing the thickness of deposited AlGaN film to a certain extent is beneficial to reducing dislocation. In addition, increasing the growth temperature can also effectively reduce the dislocation in deposited AlGaN film. Furthermore, the crystallinity of deposited AlGaN film could be improved by increasing the growth temperature. This is consistent with the dislocation discussion. The mobility of adatoms increases as the growth temperature increases. So it is easier for adatoms to find their ideal lattice points at higher temperature. Thus the dislocation and other defects can be effectively reduced and the crystal quality of deposited AlGaN film could be improved.
The structure and thermal boundary conductance of the wurtzite GaN/AlN (0001) interface are investigated using molecular dynamics simulation. Simulation results with three different empirical interatomic potentials have produced similar misfit dislocation networks and dislocation core structures. Specifically, the misfit dislocation network at the GaN/AlN interface is found to consist of pure edge dislocations with burger vector of 1 3 ⁄ 〈12 ̅ 10〉 and the misfit dislocation core has an 8-atom ring structure. Although different interatomic potentials lead to different dislocation properties and thermal conductance values, all have demonstrated a significant effect of misfit dislocations on the thermal boundary conductance of the GaN/AlN (0001) interface.
