Electrical isolation of GaN by MeV ion irradiation

The evolution of sheet resistance of n-type GaN epilayers exposed to irradiation with MeV H, Li, C, and O ions is studied in situ. Results show that the threshold dose necessary for complete isolation linearly depends on the original free electron concentration and reciprocally depends on the number of atomic displacements produced by ion irradiation. Furthermore, such isolation is stable to rapid thermal annealing at temperatures up to 900 °C. In addition to providing a better understanding of the physical mechanisms responsible for electrical isolation, these results can be used for choosing implant conditions necessary for an effective electrical isolation of GaN-based devices

Sintered Cr/Pt and Ni/Au ohmic contacts to B12P2

Citation: Frye, C. D., Kucheyev, S. O., Edgar, J. H., Voss, L. F., Conway, A. M., Shao, Q. H., & Nikolic, R. J. (2015). Sintered Cr/Pt and Ni/Au ohmic contacts to B12P2. Journal of Vacuum Science & Technology A, 33(3), 6. doi:10.1116/1.4917010Icosahedral boron phosphide (B12P2) is a wide-bandgap semiconductor possessing interesting properties such as high hardness, chemical inertness, and the reported ability to self-heal from irradiation by high energy electrons. Here, the authors developed Cr/Pt and Ni/Au ohmic contacts to epitaxially grown B12P2 for materials characterization and electronic device development. Cr/Pt contacts became ohmic after annealing at 700 degrees C for 30 s with a specific contact resistance of 2 x 10(-4) Omega cm(2), as measured by the linear transfer length method. Ni/Au contacts were ohmic prior to any annealing, and their minimum specific contact resistance was similar to l-4 x 10(-4) Omega cm(2) after annealing over the temperature range of 500-800 degrees C. Rutherford backscattering spectrometry revealed a strong reaction and intermixing between Cr/Pt and B12P2 at 700 degrees C and a reaction layer between Ni and B12P2 thinner than similar to 25 nm at 500 degrees C. (C) 2015 American Vacuum Society

Ultralight, ultrastiff mechanical metamaterials

The mechanical properties of ordinary materials degrade substantially with reduced density because their structural elements bend under applied load. We report a class of microarchitected materials that maintain a nearly constant stiffness per unit mass density, even at ultralow density. This performance derives from a network of nearly isotropic microscale unit cells with high structural connectivity and nanoscale features, whose structural members are designed to carry loads in tension or compression. Production of these microlattices, with polymers, metals, or ceramics as constituent materials, is made possible by projection microstereolithography (an additive micromanufacturing technique) combined with nanoscale coating and postprocessing. We found that these materials exhibit ultrastiff properties across more than three orders of magnitude in density, regardless of the constituent material

Ion-Beam-Defect Processes in Group-III Nitrides and ZnO

Recently, there has been much interest in wide band-gap wurtzite semiconductors such as group-III nitrides (GaN, AlGaN, and InGaN) and ZnO. Ion-beam-defect processes are considerably more complex in these wurtzite semiconductors than in the case of both elemental and group-III-V cubic semiconductors. This brief review focuses on our recent studies of the following aspects of ion-beam-defect processes: (i) effects of implanted species and the density of collision cascades, (ii) the nature of ion-beam-produced planar defects in GaN, (iii) defect production in GaN by swift heavy ions, (iv) blistering of H-implanted GaN, (v) electrical isolation of GaN and ZnO, (vi) the effect of Al and In content on defect processes in III-nitrides, and (vii) structural damage in ZnO with an intriguing effect of the formation of an anomalous defect peak. Emphasis is given to unusual ion-beam-defect processes and to the physical mechanisms underlying them

Effect of irradiation temperature and ion flux on electrical isolation of GaN

We study the evolution of sheet resistance of n-type GaN epilayers irradiated with MeV 1H and 12C ions. Results show that both implantation temperature (varied from 77 up to 423 K) and ion beam flux affect the process of electrical isolation in the case of irradiation with 12C ions. This behavior is consistent with significant dynamic annealing occurring in GaN during MeV light-ion bombardment, which suggests a scenario where the centers responsible for electrical isolation are defect clusters or anti-site-related defects. Dynamic annealing causes simple ion-beam-generated Frenkel pairs to annihilate (or cluster) during irradiation at liquid nitrogen temperature and above. These beam-flux and irradiation-temperature effects are not observed during bombardment with lighter 1H ions, which produce very dilute collision cascades. A qualitative model is proposed to explain temperature and flux effects in GaN in the MeV light-ion bombardment regime used for electrical isolation

Effect of irradiation temperature and ion flux on electrical isolation of GaN

We study the evolution of sheet resistance of n-type GaN epilayers irradiated with MeV 1H and 12C ions. Results show that both implantation temperature (varied from 77 up to 423 K) and ion beam flux affect the process of electrical isolation in the case of irradiation with 12C ions. This behavior is consistent with significant dynamic annealing occurring in GaN during MeV light-ion bombardment, which suggests a scenario where the centers responsible for electrical isolation are defect clusters or anti-site-related defects. Dynamic annealing causes simple ion-beam-generated Frenkel pairs to annihilate (or cluster) during irradiation at liquid nitrogen temperature and above. These beam-flux and irradiation-temperature effects are not observed during bombardment with lighter 1H ions, which produce very dilute collision cascades. A qualitative model is proposed to explain temperature and flux effects in GaN in the MeV light-ion bombardment regime used for electrical isolation

Electrical isolation of GaN by MeV ion irradiation

The evolution of sheet resistance of n-type GaN epilayers exposed to irradiation with MeV H, Li, C, and O ions is studied in situ. Results show that the threshold dose necessary for complete isolation linearly depends on the original free electron concentration and reciprocally depends on the number of atomic displacements produced by ion irradiation. Furthermore, such isolation is stable to rapid thermal annealing at temperatures up to 900 °C. In addition to providing a better understanding of the physical mechanisms responsible for electrical isolation, these results can be used for choosing implant conditions necessary for an effective electrical isolation of GaN-based devices