Cole Ritter

Synthesis of ternary SiGeSn semiconductors on Si(100) via SnxGe1−x buffer layers

Single-phase Si1−x−yGexSny alloys with random diamond cubic structures are created on Si(100) via ultrahigh vacuum chemical vapor deposition reactions of SnD4 with SiH3GeH3 at 350 °C. Commensurate heteroepitaxy is facilitated by Ge1−xSnx buffer layers, which act as templates that can conform structurally and absorb the differential strain imposed by the more rigid Si and Si–Ge–Sn materials. The crystal structure, elemental distribution and morphological properties of the Si1−x−yGexSny/Ge1−xSnx heterostructures are characterized by high-resolution electron microscopy, including electron energy loss nanospectroscopy, x-ray diffraction (rocking curves) and atomic force microscopy. These techniques demonstrate growth of perfectly epitaxial, uniform and highly aligned layers with atomically smooth surfaces and monocrystalline structures that have lattice constants close to that of Ge. Rutherford backscattering ion channeling shows that the constituent elements occupy random substitutional sites in the same ave...

Synthesis of uniform GaN quantum dot arrays via electron nanolithography of D2GaN3

We demonstrate the deposition of periodic arrays of uniformly sized GaN quantum dots onto a SiOx substrate. The dots are deposited using a nanolithography technique based on a combination of electron-beam-induced chemical vapor deposition and single-source molecular hydride chemistries. Under appropriate deposition conditions, we can deposit uniform dots of height 5 nm and full widths at half-maxima of 4 nm. The dot size is controlled by the spatial distribution of secondary electrons leaving the substrate surface. The smallest, most uniform void-free dots are created via nanolithography of molecules adsorbed on the substrate surface.

Low-temperature pathways to Ge-rich Si1−xGex alloys via single-source hydride chemistry

We report rapid low-temperature (300–470°C) growth of Si0.50Ge0.50, Si0.33Ge0.67, Si0.25Ge0.75, and Si0.20Ge0.80 alloys on Si(100) using heavy single-source hydride molecular compounds (H3Ge)nSiH4−n (n=1–4). Incorporation of the entire SiGe, SiGe2, SiGe3, and SiGe4 framework of these precursors into the film provides precise control of morphology, composition, and strain. Low-energy electron microscopy analysis indicates that the (H3Ge)xSiH4−x (x=2–4) species are highly reactive, with H2 desorption characteristics comparable to those of Ge2H6, despite the presence of strong Si–H bonds in their molecular structure.

Low-temperature GaN growth on silicon substrates by single gas-source epitaxy and photo-excitation

We report a unique low-temperature growth method for epitaxial GaN on Si(111) substrates via a ZrB2(0001) buffer layer. The method utilizes the decomposition of a single gas-source precursor (D2GaN3)3 on the substrate surface to form GaN. The film growth process is further promoted by irradiation of ultraviolet light to enhance the growth rate and ordering of the film. The best epitaxial film quality is achieved at a growth temperature of 550°C with a growth rate of 3nm∕min. The films exhibit intense photoluminescence emission at 10K with a single peak at 3.48eV, indicative of band-edge emission for a single-phase hexagonal GaN film. The growth process achieved in this study is compatible with low Si processing temperatures and also enables direct epitaxy of GaN on ZrB2 in contrast to conventional metalorganic chemical vapor deposition based approaches.