H. Boudinov

Electrical isolation in GaAs by light ion irradiation: The role of antisite defects

The evolution of the sheet resistance (Rs) in n‐type GaAs layers during ion irradiation was studied using light mass projectiles like proton, deuterium, and helium ions at various energies. For all the cases, at the beginning of the irradiation, Rs increases with the accumulation of the dose. After reaching ≊109 Ω/⧠, Rs saturates, forming a plateau. This plateau is succeeded by a decreasing of Rs with the increase of the dose, denoting that conduction via damage‐related mechanisms is taking place. The threshold dose to convert the conductive layer to a highly resistive one at room temperature or at 100 °C is found to scale with the inverse of the estimated number of displaced lattice atoms along the depth of the doped layer. Antisite defects formed by the replacement collisions are invoked to play the major role in isolation formation in GaAs by virtue of their lower sensitivity to dynamic annealing compared to other point defects.

Electronic stopping power of 〈100〉 axial-channelled He ions in Si crystals

Abstract Measurements of the electronic stopping power of He2+ ions along the 〈100〉 direction in Si crystal with energies ranging between 200 keV and 4.5 MeV are presented. The Rutherford backscattering technique has been used with SIMOX samples consisting of a Si single-crystal layer on top of a buried layer of 500 nm SiO2 built into a Si 〈100〉 wafer.

A novel Voltage-mode CMOS quaternary logic design

This brief presents a novel kind of voltage-mode CMOS design that uses multiple threshold voltage transistors and three power supply lines to implement quaternary logic gates, showing lower power dissipation and using less area than the present voltage-mode quaternary circuits. Inverter, NMIN, and NMAX gates are simulated with the Spice tool using TSMC 0.18-/spl mu/m technology. The proposed logic circuits overcome the limitations of previous implementations used for multiple-valued logic circuits, such as static power consumption and noise vulnerability.

Electrical isolation of GaN by MeV ion irradiation

This work was partly supported by Conselho Nacional de Pesquisas (CNPq, Brazil) under Contract No. 200541/ 99-4.

Thermal stability of the electrical isolation in n-type gallium arsenide layers irradiated with H, He, and B ions

The stability of the electrical isolation in n-type GaAs layers irradiated with ions of different mass is compared. The irradiations were performed with proper doses of 1H+, 4He+, or 11B+ ions to create specific damage concentration level which lead to: (i) the trapping of practically all the carriers (Rs ≈108 Ω/□), (ii) the onset of hopping conduction (Rs ≈108 Ω/□), and (iii) a significant hopping conduction (Rs ≈106 Ω/□). Irrespectively of the ion mass, the temperature range for which the isolation is preserved, i.e., Rs >108 Ω/□, extends up to 200 or ≈ 600 °C, respectively, for the cases (i) and (ii). In case (iii), this range comprises temperatures from ≈ 400 to 650 °C. Annealing stages at 200 and 400 °C recover in a great extent the conductivity and improve the carrier mobility in low dose irradiated samples [case (i)]. In samples irradiated to higher doses [cases (ii) and (iii)], the conductivity recovers in a single stage.

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.

Quaternary Look-Up Tables Using Voltage-Mode CMOS Logic Design

Data processing optimization is one of the main concerns for developing of multiple-valued logic. An advantage could be achieved by realization of new functions existing in non-binary logic. These new logic functions could be implemented using quaternary look-up tables. In this work, a quaternary multiplexer circuit is designed to implement any n-variable quaternary logic function based on its truth table. Voltage-mode CMOS with multi-threshold transistors and multi-Vdd quaternary design was suggested. The multiplexer circuit consists of quaternary down literal circuits, binary inverters and binary pass transistor gates. All circuits were simulated with the Spice tool using TSMC 0.18 mum technology and have shown improvements in performance and power consumption and using less transistors than their equivalent binary circuits.

Electrical isolation of n-type and p-type InP layers by proton bombardment

This work was partly supported by Conselho Nacional de Pesquisas (CNPq, Brazil) under Contract No. 200541/ 99-4.

ENHANCED ELECTRICAL ACTIVATION OF INDIUM COIMPLANTED WITH CARBON IN A SILICON SUBSTRATE

Electrical activation of In of 18%–52% of the implanted dose (5×1014 cm−2) was obtained in Si samples having a C+ coimplantation after rapid thermal annealing (RTA) at 800–1000 °C for 15 s. This electrical activation yield markedly contrasts with that in samples singly implanted with In in which only ≅0.5% of the dose was activated. The following features were observed in the coimplanted samples: (i) a reverse annealing of the electrical activation in the temperature range of 800–900 °C; (ii) significant reduction of the In profile redistribution during RTA; and (iii) the electrically activated In concentration is substantially higher than the substitutional In concentration. These findings are discussed in terms of the interaction between C atoms and Si self-interstitials (SiI), strain compensation between C and In atoms in the Si lattice, and formation of stable In substitutional–C substitutional acceptors centers.

Ion beam mixing of Fe thin film and Si substrate

Abstract Samples consisting of thin Fe film (40 nm) deposited on (100) Si substrate were irradiated at different temperatures with a Xe + beam (0.2−2.0 × 10 16 cm −2 at 380 keV) and analysed by Rutherford backscattering spectrometry (RBS) and conversion electron Mossbauer spectrometry (CEMS). The intermixing was found to be controlled by cascade mixing when performed at temperatures below ⋍160°C and by radiation enhanced diffusion (RED) at higher temperatures. A combination of Fe 3 Si, FeSi and β-FeSi 2 phases composes the intermixed layer, being the latter phase the predominant compound product, for T ≤ 300°C. When Xe + irradiation is conducted at 400°C the α-FeSi 2 phase is additionally formed. In this case the most abundant phases are Fe 3 Si and FeSi.