PAMBE Growth and Characterization of Superlattice Structures in Nitrides

by Jing Yang

Institution: The Ohio State University
Department: Materials Science and Engineering
Degree: PhD
Year: 2013
Keywords: Materials Science; PAMBE, MQWs, SL, Structural Characterization
Record ID: 2011372
Full text PDF: http://rave.ohiolink.edu/etdc/view?acc_num=osu1376986760


Superlattice structures formed using the III- nitrides family of semiconductors have attracted a great deal of attention due to some unique properties. Within the III-nitrides, the large conduction band offset between GaN/AlN and InN/AlN provides very large electron confinement that could be useful for ultrafast intersubband-based photonics. Second, the large spontaneous polarization difference at any nitrides heterostructure interface coupled with the large lattice mismatch (3%-13%), shows the potential for polarization-driven applications. Finally, the epitaxial integration of rare earth pnictides (RE-Pn), such as ErAs and ErSb, in III-As semiconductors has been intensively studied due to the applications in novel high speed photodetectors and photoconductive switches. They motivate the parallel work of embedding GdN in a GaN matrix such as a superlattice structure. In the first part of this thesis, the growth of InN/AlN multiple quantum well structures by plasma assisted molecular beam epitaxy is presented. The InN/AlN multiple quantum wells are grown on top of coalesced AlN nanocolumns on Si(111) substrates. The structural and optical properties of InN/AlN quantum wells are thoroughly studied by scanning transmission electron microscopy, x-ray diffractometry and photoluminescence. STEM confirms the formation of InN quantum wells between AlN barriers. XRD data indicate the successful tuning of the ultra-thin InN quantum well thicknesses from sample to sample. Photoluminescence measurements show emission in the visible that shifts as a function of quantum well thickness. Moreover, the time decay of PL from the different quantum wells is detected by time correlated single photon counting. In order to study the effects of growth conditions on interface sharpness in GaN/AlN superlattices, we investigate the possibility and demonstrate the success of using growth temperature above the GaN decomposition during the deposition of GaN/AlN superlattices in the second part this work. This high temperature growth condition is compared to well-established low temperature conditions. For superlattices grown thinner than their critical thickness, the N-rich high-temperature sample displays slightly superior structural quality. Reciprocal space mapping has been conducted to study the different relaxation mechanisms in high temperature and low temperature growth conditions. In the third part of the thesis, we report on the integration of the RE-Pn GdN as discrete particles in a GaN matrix, as well as the formation of a GdN/GaN superlattice structure. It is hypothesized that the growth of GdN particles proceeds in a similar fashion to that of Re-Pn in III-As zincblende systems, with initial Re-Pn island formation followed by overgrowth of the surrounding uncovered III-As matrix. Periodic structures of GdN nano-island layers spaced between GaN regions were prepared and subsequently characterized by a variety of methods. High resolution XRD shows that the cubic rock-salt GdN islands are epitaxially oriented to the hexagonal wurtzite…