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Plasma-Assisted MBE of III-nitride semiconductors: From two-dimensional layers to nanostructures

Eva Monroy 

CEA-CNRS,Institut Nanosciences et Cryogénie, 17 rue des Martyrs, Grenoble 38054, France


Due to the low growth temperature and in-situ monitorization capabilities, Molecular-Beam Epitaxy (MBE) is the most suitable growth technique for devices or structures with low dimensionality, critical interface sharpness or immiscibility challenges. This talk will start with an introduction to plasma-assisted MBE of III-nitride materials, discussing the surface energy role on the control of the growth morphology. For growth temperatures high enough to grant a certain mobility of the group-III species at the growing front (>700°C in the case of GaN), variations of the III/V flux ratio result in changes of the surface potential that allow switching from Frank-Van der Merwe to Stranski-Krastanow growth mode. The transition from two-dimensional to three-dimensional growth can also be induced by a growth interruption due to the variation of the surface stoichiometry associated to the metal desorption in vacuum. The application of these principles to the synthesis of (0001)-, (000-1)- and (11-22)-oriented nanostructures (quantum wells, quantum dots) will be addressed, paying attention to the particularities of those surfaces in terms of adatom mobility and metal wetting properties. Starting from the growth diagrams of the various GaN faces, we will study the incorporation of In or/and Al to form ternary or quaternary compounds. The modification of the growth kinetics in presence of dopants (Si, Mg, Mn) will be analyzed. The growth of a complete device structure requires specific growth processes, conditioned by the less thermally stable layer and by the specifications in terms of interface quality. Interfacial reactions, defects and interdiffusion will be discussed for the case of GaN/AlGaN and GaN/InGaN.

The advantages of plasma-assisted MBE find direct application in GaN/AlGaN intersubband (ISB) optoelectronics, technology that requires the control of the nanostructure dimensions and interface sharpness at the atomic scale. III-nitride heterostructures are excellent candidates for high-speed ISB devices thanks to their large conduction band offset (~1.8 eV for the GaN/AlN system) and subpicosecond ISB scattering rates. However, due to the rather large GaN electron effective mass (m* = 0.2m0), quantum wells as thin as 1-1.5 nm are required to achieve ISB absorption at 1.3-1.55 µm. In this talk, we will summarize the latest achievements in terms of MBE growth and characterization of ultra-thin GaN/Al(Ga)N QW and QD superlattices in polar and semipolar crystallographic orientations for the fabrication of ISB optoelectronic devices.

Fig. 1. GaN/AlN nanostructures (quantum wells, nanorods, quantum dots) synthesized by plasma-assisted MBE in various crystallographic orientations.

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Related papers

Presentation: Invited oral at 17th International Conference on Crystal Growth and Epitaxy - ICCGE-17, General Session 10, by Eva Monroy
See On-line Journal of 17th International Conference on Crystal Growth and Epitaxy - ICCGE-17

Submitted: 2013-07-05 17:10
Revised:   2013-07-11 17:12