Radical reduction of III–V device costs requires a multifaceted approach attacking both growth and substrate costs. Implementing device removal and substrate reuse provides an opportunity for substrate cost reduction. Controlled spalling allows removal of thin devices from the expensive substrate; however, the fracture‐based process currently generates surfaces with significant morphological changes compared to polished wafers. 49 single junction devices are fabricated across the spalled surface of full 50 mm germanium wafers without chemo‐mechanical polishing before epitaxial growth. Device defects are identified and related to morphological spalling defects—arrest lines, gull wings, and river lines—and their impact on cell performance using physical and functional characterization techniques. River line defects have the most consistent and detrimental effect on cell performance. Devices achieve a single junction efficiency above 23% and open‐circuit voltage of 1.01 V, demonstrating that spalled germanium does not need to be returned to a pristine, polished state to achieve high‐quality device performance.

Molecular beam epitaxy offers an exciting avenue for investigating the behavior of the topological semimetal $\mathrm{C}{\mathrm{d}}_3\mathrm{A}{\mathrm{s}}_2$, by providing routes for doping, alloying, strain engineering, and heterostructure formation. To date, however, minimal exploration has been devoted to the impact of defects that are incorporated into epilayers due to constraints imposed by the substrate and narrow growth window. Here, we use a combination of lattice-matched $\mathrm{Z}{\mathrm{n}}_x\mathrm{C}{\mathrm{d}}_{1-x}\mathrm{Te}$ buffer layers, miscut substrates, and broadband illumination to study how dislocations, twins, and point defects influence the electron mobility of $\mathrm{C}{\mathrm{d}}_3\mathrm{A}{\mathrm{s}}_2$. A combination of defect suppression approaches produces $\mathrm{C}{\mathrm{d}}_3\mathrm{A}{\mathrm{s}}_2$ epilayers with electron mobilities upwards of $15000\mathrm{c}{\mathrm{m}}^2/\mathrm{V}\mathrm{s}$ at room temperature.

The extent to which disorder influences the properties of topological semimetals is relevant to the understanding of topological states and their use in practical applications. Using molecular beam epitaxy, we achieve systematic control of point defect concentrations in the prototypical Dirac semimetal ${\mathrm{Cd}}_3{\mathrm{As}}_2$ to gain insight into the role of disorder on electron transport behavior. Using the guiding center diffusion model for linear magnetoresistance, we extract point defect densities as a function of deposition conditions. We find that reducing cadmium defect concentrations by an order of magnitude results in an $2\times$ increase in the magnetoresistance from 450% to 900%. This finding yields important information in the quest to identify the origin of linear magnetoresistance in a wider range of materials.

The valence-band offsets, ΔE_v, between semiconducting half-Heusler compound CoTiSb and lattice-matched III-V In_0.53Ga_0.47As and In_0.52Al_0.48As heterojunction interfaces have been measured using X-ray photoemission spectroscopy (XPS). These interfaces were formed using molecular beam epitaxy and transferred in situ for XPS measurements. Valence-band offsets of 0.30 eV and 0.58 eV were measured for CoTiSb/In_0.53Ga_0.47As and CoTiSb/In_0.52Al_0.48As, respectively. By combining these measurements with previously reported XPS ΔE_v (In_0.53Ga_0.47As/In_0.52Al_0.48As) data, the results suggest that band offset transitivity is satisfied. In addition, the film growth order of the interface between CoTiSb and In_0.53Ga_0.47As is explored and does not seem to affect the band offsets. Finally, the band alignments of CoTiSb with GaAs, AlAs, and InAs are calculated using the density function theory with the HSE06 hybrid functional and applied to predict the band alignment of CoTiSb with In_0.53Ga_0.47As and In_0.52Al_0.48As. Good agreement is found between the calculated valence-band offsets and those determined from XPS.

ZnGeN₂ is a potential green-to-amber emitter which can be integrated into existing GaN LED heterostructures due to structural similarity. However, for accurate material characterization, ZnGeN₂ must be grown without GaN due to their similar optical and structural properties. This is exemplified by ZnGeN₂/GaN heterostructures with luminescence signatures that overlap a well-known Zn-doped GaN blue luminescence band. In this work we present the molecular beam epitaxy growth of ZnGeN₂ on lattice mismatched AlN templates with regrown AlN buffer layers enabling GaN-free structural and optical characterization. Fully relaxed ZnGeN₂ on AlN shows cation-disordered lattice parameters a = 3.1962 Å ± 0.0032 Å and c = 5.2162 Å ± 0.0015 Å (c/a ratio = 1.632) determined from multiple reflections and a least-squares regression. Reflection high-energy electron diffraction, X-ray diffraction, and atomic force microscopy characterization reveal an optimal growth temperature for ZnGeN₂ on AlN of 450 °C. Photoluminescence shows broad recombination centered around 2.96 eV, clearly attributed to ZnGeN₂, which is distinct from the 2.88 eV Zn-doped GaN blue luminescence band. This work offers insight into the properties of ZnGeN₂, enabling new characterization and new heteroepitaxial devices based on AlN.

Device applications of topological semimetals await the development of epitaxial films in the ultrathin limit. Weak antilocalization (WAL) has been extensively utilized in the understanding of surface states in topological insulators and shows promise for use in elucidating the properties of thin film topological semimetals. Here, we report insights from WAL in the surface state and interface transport properties of our recently synthesized single-crystal-like thin films of the Weyl semimetal TaAs(001) grown on GaAs(001). We observe robust, anisotropic WAL in the magnetoconductance from 2 to 20 K in films from 10 to 200 nm thick. We link the anisotropic WAL magnetoconductance to anisotropic mobility stemming from film topography. We conclude that WAL in the films likely originates from the antilocalization of topological surface states. The WAL magnetoconductance is impacted by the film thickness and topography, solidifying the useful role of WAL in the study of topological semimetal/semiconductor heterointerfaces. Published by the American Physical Society 2024