Droplet Controlled Growth Dynamics in Molecular Beam Epitaxy of Nitride Semiconductors

Mani Azadmand,Daniel Chrastina,Maurizio Acciarri,Luca Barabani,Richard Nötzel,Alexey Fedorov,Sergio Bietti,Stefano Sanguinetti,Shiro Tsukamoto,Emiliano Bonera

doi:10.1038/s41598-018-28984-9

Abstract

The growth dynamics of Ga(In)N semiconductors by Plasma-Assisted Molecular Beam Epitaxy (PAMBE) at low temperatures (T = 450 °C) is here investigated. The presence of droplets at the growth surface strongly affects the adatom incorporation dynamics, making the growth rate a decreasing function of the metal flux impinging on the surface. We explain this phenomenon via a model that considers droplet effects on the incorporation of metal adatoms into the crystal. A relevant role is played by the vapor-liquid-solid growth mode that takes place under the droplets due to nitrogen molecules directly impinging on the droplets. The role of droplets in the growth dynamics here observed and modeled in the case of Nitride semiconductors is general and it can be extended to describe the growth of the material class of binary compounds when droplets are present on the surface.

Highlights

The different binding energies of In-N and Ga-N bonds are reflected in the different decomposition temperatures of InN (630 °C) and GaN (850 °C)[13]
There is still little knowledge about the exact growth dynamics of InGaN in the low temperature regime and the role that is played by the metal droplets that form at the surface in the metal-rich conditions
In this study we demonstrate that the droplets have a fundamental role in determining the InGaN growth dynamics determining the adatoms kinetics of incorporation in the presence of droplets

Summary

Epitaxy of Nitride Semiconductors

Mani Azadmand[1], Luca Barabani[1], Sergio Bietti[1], Daniel Chrastina 2, Emiliano Bonera[1], Maurizio Acciarri[1], Alexey Fedorov[3], ShiroTsukamoto[1], Richard Nötzel4 & Stefano Sanguinetti 1. Low growth temperatures have been used to avoid InN decomposition and In desorption, allowing the growth of high-In-composition InGaN layers by plasma-assisted molecular beam epitaxy (PAMBE)[10,22,23,24] At these temperatures, metal-rich conditions lead to the formation of droplets on the surface which affect the film quality[25] and that are difficult to remove by thermal treatment, because the In-N dissociation temperature is lower than the onset temperature for the evaporation of In from the In droplets on the InGaN surface[26]. Several method to overcome such drawback have been proposed, based on the alternating sequence of metal-rich and nitrogen-rich conditions at low temperature to take profit of the higher mobility of metal adatoms in metal-rich conditions and to eliminate the metal droplets that form on the surface during the atomic nitrogen irradiation in absence of metal flux[23,29,30]

Sample ABCDEFGHIJK

Results and Discussion

Conclusion

Author Contributions

Additional Information