Saafie Salleh

Range distribution and electronic stopping power for Cobalt (Co) ions in Gallium Arsenide (GaAs) optoelectronic devices

Studies for introduction of atoms into a solid substrate by bombardment of the solid with ions in the electron-volt (eV) to mega-electron-volt (MeV) energy range have always received great interest. Gallium Arsenide (GaAs) is a basic material for most of the III-V based electronics, and, therefore, lends itself for applications where this is of concern. In this paper, the damage evolution due to photon energy deposition of Cobalt (Co) is being simulated in GaAs material using SRIM (Stopping and Range of Ions in Matter). Besides, TRIM (The Range of Ions in Matter) calculation also gives the amount of nuclear energy deposited in the collisions and recoil events. From the findings of this research, it is found that exposure to high energy photon irradiation causes a degradation of the electrical parameters of GaAs layer and this is mainly caused by the displacement damage.

Effects of high energy neutrons and resulting secondary charged particles on the operation of MOSFETs

Study for penetration of nuclear radiation into semiconductor materials had been of theoretical interest and of practical important in these recent years, driven by the scaling down of semiconductor materials. This paper reviews the typical effects occurring in the operation of MOSFETs due to irradiation with neutrons resulting from Deuterium-Tritium (D-T) reaction. Charge trapping features of MOSFETs were investigated by in situ irradiation and post irradiation methods. Analytical explanations and calculations on the numeric change that occurs in the MOSFETs were conducted using a series of simulations. The oxide insulating layer of MOSFET is found to be most sensitive to the neutron radiation. Energy deposition of neutrons in MOSFET occurs via two mechanisms; firstly by trapped charge buildup in the silicon dioxide (SiO2) layer and secondly, an increase in the density of trapping states at the SiO2 interface. The bombardment of neutron in the MOSFET model produces at least three secondary particles, which are alpha (α) particles, proton (p) particles and silicon recoil atoms, through the reactions of (n,α), (n,p) and neutron scattering respectively. Damage efficiencies of these secondary particles are discussed in direct comparisons.

Defect Generation in Bipolar Devices by Ionizing Radiation

This paper reviews typical effects occurring in bipolar junction transistors (BJTs) due to gamma (γ) rays irradiation. The detrimental consequences of this interaction can be categorized into two: the transfer of energy to electrons due to ionization and electronic excitations; and also the transfer of energy to atomic nuclei. The radiation damage induced by this interaction was studied using in situ method by comparing the currentvoltage characteristics of the devices under test (DUTs) at different biased collecting current and operating modes. The high energy from gamma radiation is found to induce both temporarily and permanent damage in the DUTs depending on the current drive and total dose absorbed. The most significant radiation damage in the BJT is the creation of electron-hole pairs which increases the probability of recombination at the base region of BJTs. The DUTs are found to exhibit minor annealing effect at post-irradiation and the results also show that devices operating in higher bias current are more capable of withstanding the effect by gamma radiation.

Simulation of ionizing radiation induced effects in nanoscale semiconductor material

Study for defect in semiconductors induced by ionizing radiation has become much more sophisticated in this recent year, driven by the current development in the ongoing miniaturization of silicon (Si) semiconductor industry. In this paper, the damage evolution due to Cobalt-60 (Co-60) is being simulated in nanoscale Silicon layer using SRIM (Stopping and Range of Ions in Matter). SRIM is a computer simulation that uses Monte Carlo method and it contains TRIM (The Range of Ions in Matter) calculation. The SRIM-TRIM calculates the range of ions in matter using collisions of ions-atoms. Besides, the radiation tolerance of the silicon layer is compared when its thickness is scaling down to nano dimension. From the findings, it is observed that the penetration of Co-60 ions into the target silicon layer leads to production of lattice defects in the form of vacancies, defect clusters and dislocations. These can alter the material parameters and hence the properties of the devices. The simulation results also show that nanoscale silicon layer features improved radiation robustness against ionizing radiation, in term of displacement damage.

The Propagation Losses of Cold Deposited Zinc Sulfide Waveguides

Zinc sulfide (ZnS) waveguides with the thickness of 0.5 μm have been deposited onto oxidized silicon wafer substrates at cold temperature (Tcold = –50°C) and ambient temperature (Tambient = 25°C) by thermal evaporation technique. The propagation losses of ZnS waveguides were determined by a scattering detection method. The propagation losses of cold deposited ZnS waveguide were 20.41, 11.35, 3.51 and 2.30 dB/cm measured the wavelengths of 633, 986, 1305 and 1540 nm, respectively. Where as, the propagation losses of ambient deposited ZnS waveguide were 131.50, 47.99, 4.43 and 2.74 dB/cm measured the wavelengths of 633, 986, 1305 and 1540 nm, respectively. The propagation loss of the cold deposited ZnS waveguide was dominated by surface scattering whereas the propagation loss of the ambient deposited ZnS waveguide was dominated by bulk scattering.

A model for neutron radiation damage in Metal Oxide Semiconductor (MOS) structures

Neutron bombardment on semiconductor material causes defects, one such primary physical effect is the formation of displacement defects within the crystal lattice structure, and such defects effectively decrease the mean free path and thus shorten the recombination time. Ionizing radiation causes creation of electron-hole pair in the gate oxide and in parasitic insulating layers of the MOS devices. Calculations show increase of the dark current in depletion region caused by a single neutron. Determination of energy and angular distribution of primary knock on atoms, with 14 MeV neutron irradiation in silicon are presented.

Influence of substrate temperature and post annealing of CuGaO2 thin films on optical and structural properties

A transparent p-type thin film CuGaO2 was deposited by using RF sputtering deposition method on plastic (PET) and glass substrate. The characteristics of the film is investigated. The thin film was deposited at temperature range from 50-250°C and the pressure inside the chamber is 1.0×10−2 Torr and Argon gas was used as a working gas. The RF power is set to 100 W. The thickness of thin film is 300nm. In this experiment the transparency of the thin film is more than 70% for the visible light region. The band gap obtain is between 3.3 to 3.5 eV. The details of the results will be discussed in the conference.

Temperature dependence of Ga:ZnO film deposited by RF magnetron sputtering

This paper investigate the dependence of substrate temperature onto characteristic of Gallium doped Zinc Oxide (Ga:ZnO). Ga:ZnO films were deposited on a glass substrate by RF Magnetron Sputtering using Ga:ZnO ceramic target with 99.99% purity. Sputtering power, argon flow and target distance were fixed in order to investigate the influence of substrate temperature to the growth characteristic, structural and optical properties of the films. Sputtering was performed with RF power of 100 Watt and the argon flow in was set at 10 sccm. The deposition times were fixed at 40 minute for all films. The result shows growth rate for Ga:ZnO growth at higher temperature are lower than at room temperature. Ga:ZnO thin films on different substrate temperature were successfully deposited onto glass substrate. All films are polycrystalline with (0 0 2) preferential orientation and fully transparent films with high transparency over 80 percent were achieved.

Cold deposition of zinc sulfide optical waveguides using thermoelectric device

Zinc sulfide (ZnS) thin films as the waveguide medium have been deposited onto oxidized silicon wafer substrates at cold temperature (Tcold = –50oC) and ambient temperature (Tambient = 25oC) by thermal evaporation technique. The surface morphology of ZnS films were pictured with an atomic force microscopy (AFM) and the surface roughness were calculated from the AFM images. The propagation losses of the samples were measured using a scanning detection technique attached to a prism coupler. The AFM results revealed that the surface of cold deposited ZnS film is rougher than the surface of ambient deposited ZnS film. The propagation losses of the cold deposited ZnS waveguide are consistently lower than the ambient deposited ZnS waveguide at all measured wavelengths.

Surface roughness of thermally evaporated ZnS optical waveguides

In this study, the propagation loss and the surfaces of ZnS thin films on silicon substrates have been investigated. ZnS thin films have been prepared by thermal evaporation at two different substrate temperatures, which were at ambient temperature and at /spl deg/50/spl deg/C. The propagation losses were measured with scanning detection technique attached to a prism coupling and the thin film surfaces were characterized with an atomic force microscope. The waveguide propagation loss of ambient deposited film is 131.50 dB/cm whereas the loss of cold deposited film is 20.41 dB/cm. The surface roughness of the waveguide is enhanced for cold evaporated ZnS film.