Deep-level defects and diffusion length measurements in low energy proton-irradiated GaAs

A detailed characterization of deep-level defects induced by low energy proton irradiation in n-GaAs LPE layer using AlGaAs-GaAs mesa structure has been carried out for several proton energies (i.e., 50 100 and 290 kev) and fluences (i.e., 10¹⁰, 10¹¹, and 10¹² p/cm²), using DLTS, SEM-EBIC, I-V and C-V measurement techniques. Important defect and recombination parameters such as density and energy level of electron and hole traps, thermal emission rates and capture cross sections for electrons and holes in each trap level as well as hole diffusion lengths in the n-GaAs LPE layer were deduced from these measurements. Hole diffusion lengths determined by the EBIC, DLTS, and I-V measurements are found in good agreement. It is shown that dark current under forward bias condition was dominated by recombination of electron-hole pairs via deep level defects in the junction space charge region of the diode. Significant carrier removal occurs for proton fluence greater than 10¹³p/cm². Research supported by NASA Langley Research Center under grant No. NSG-1425.     

Characterization of Annealing of Co60 Gamma-Ray Damage at the Si/Si02 Interface

The annealing of Co60 gamma-ray damage at the Si/SiO2 interface is a well behaved phenomenon. Based on the characterization of annealing over a temperature range of 25° to 300°C, a physical model is developed. This model suggests that the annealing of the radiation damage occurs in two phases: first, the Qf-like trapped positive charges are converted to acceptor-like fast-states, and second, the fast-states are gradually annihilated. Both of these phases occur at an accelerated rate at a given temperature in presence of hydrogen. The densities of trapped positive charges and fast-states reach saturation levels which depend on the level of radiation (dose rate), and the temperature. The tolerance level of an IC to radiation exposure depends on these saturation levels. The experimental results also indicate that the positive charges are trapped at the Si/SiO2 interface even if a negative gate-bias is applied during irradiation. Furthermore, it is unambiguously observed that once the holes are trapped at the interface, they do not move along the interface even under applied biases, but they move only toward Si where they become acceptor-like fast-states.     

Nanoscale rapid melting and crystallization of semiconductor thin films

The current study details nanosecond laser-based rapid melting and crystallization of thin amorphous silicon (a-Si) films at the nanoscale using two different optical near-field processing schemes. Both apertureless and tapered fiber near-field scanning optical microscope probes were utilized to deliver highly confined irradiation on the target surface. The various modification regimes produced as a result of the rapid a-Si melting and crystallization transformations were shown to critically depend on the applied laser fluence. Consequently, the crystallized pattern morphology and feature size could be finely controlled. High energy density was observed to impart ablation surrounded by a narrow melt ring. At much lower incident laser energy density, single nanostructures with a lateral dimension of approximately 90 nm were defined.     

Growth characteristics of LPE InSb and InGaSb

Growth characteristics of InSb and In_l-xGa_xSb (x < 0.09) prepared by infinite solution epitaxy are investigated. Substrate surface contamination is found to be a controlling factor in epitaxial layer continuity and surface morphology; as the degree of contamination decreases, growth varies from discontinuous to terraced continuous to terrace-free continuous. The dependence of layer thickness on growth parameters is consistent with a diffusion-controlled process in which the Sb diffusion coefficient D is given by D = 1.1 × 10⁻³ exp[(-0.43 eV)/kT] cm² sec⁻¹. Electron microprobe analysis of the Ga distribution through epitaxial layers indicates that Ga diffuses fast enough in the solution under typical growth conditions to maintain a constant ternary composition.     

Interpretation of non-equilibrium measurements on MOS devices using the linear voltage ramp technique

An analytical and experimental study is presented of MOS devices subjected to a linear voltage ramp such that the rate of change of voltage is sufficiently high to take the device into the non-equilibrium mode of operation. Various areas of the resulting current-voltage plots are identified with physical quantities such as gate charge and surface potential, a knowledge of which is very useful in studying non-equilibrium mechanisms. To circumvent the difficulty of tedious graphical integration involved in the process of extracting these quantities from the experimental current-voltage plots, an experimental technique is presented which facilitates the direct measurement of these quantities. The resulting plots of displacement current, surface potential and gate charge vs gate voltage are related to each other in a manner which gives interesting insight into the mechanisms occurring within the device, and agreement with the existing theories is found to be extremely good.     

Effect of crystallographic defects on the reverse performance of 4H-SiC JBS diodes

A quantitative analysis of the effect of crystallographic defects on the performance of 4H-SiC junction barrier Schottky (JBS) diodes was performed. It has been shown that higher leakage current in diodes is associated with a greater number of elementary screw dislocations. Further, threading dislocation pair arrays were observed in some of the fabricated devices and, for the first time, the role of such defects on JBS reverse leakage currents is investigated.     

Magnetorheological finishing of grooved drum surface and its performance analysis in winding process

The fine level finishing of grooved drum surfaces is an essential requirement for enhancing the performance of the winding machines in today’s textil     

Development of sensitive and specific multiplex PCR method for the detection of microcystin producing cyanobacteria in spirulina food supplements

Food Science and Biotechnology - Spirulina has emerged as the next-generation dietary supplement owing to its health benefits. Despite the advantages, there have been reports of contamination by...