T.D.M. Weijers

Crystal size and oxygen segregation for polycrystalline GaN

The authors would like to acknowledge the support of a U. S. NICOP Contract, No. N00014-99-1-GO17 sponsored through the U. S. Office of Naval Research. One of the authors (K.S.A.B.) would like to further acknowledge the support of a Macquarie University Research Fellowship.

Unique capabilities of heavy ion elastic recoil detection with gas ionization detectors

Abstract Specific aspects of heavy ion elastic recoil detection (ERD) with gas ionization detectors have been studied using representative measurements. A particular strength of the technique is the detection and direct quantification of elements with atomic numbers in the range Z=2–8, which are often not accessible with other ion beam techniques. Within the wider spectrum of analytical techniques in materials science, heavy ion ERD has unique capabilities, when the particular problem requires in addition the analysis of heavy elements or hydrogen detection. Whenever only heavy element analysis or only hydrogen profiling is of interest, alternative techniques tend to be superior.

Simultaneous Hydrogen Detection with an ERD Gas Ionization Detector

Abstract A large solid-angle gas ionization detector is shown to be capable of simultaneous hydrogen detection during heavy-ion elastic recoil detection of heavier elements. Different modes of detection are possible depending on the specific application. These include a transmission-mode in which the primary ion energy and gas-pressure in the detector are optimized for heavy-ion detection and energy loss signals are recorded for each hydrogen recoil. Alternatively, the primary ion energy can be reduced and the gas pressure in the detector increased so that the recoiled protons are fully stopped in the detector. In this case, a conventional total energy signal can be recorded. The transmission mode is shown to be particularly suited to determining the total hydrogen content of thin films, where the emphasis is on optimum mass and depth resolution for the heavy elements, whilst the stopped mode allows simultaneous hydrogen profiling with reasonable depth resolution.

Accurate depth profiling through energy-dependent pulse height deficit compensation in gas ionization detectors

Abstract The impact of the pulse height deficit effect in gas ionization detectors on the accurate extraction of depth information from heavy ion elastic recoil detection spectra has been investigated. Thin GaN films and GexSi1−x/Si heterostructures have been analyzed with a 200 MeV 197 Au beam. Employing an empirical parameterisation of the pulse height deficit, a global energy calibration of the detector can be achieved. Energy spectra have been compared, calibrated with either a constant or a full energy-dependent compensation for the deficit. A constant compensation results in significant distortion of the extracted depth profile for heavier ions, whereas an energy-dependent compensation yields true concentration–depth profiles.

Measurements of Si Ion Stopping in Amorphous Silicon

The stopping of Si-28 ions in polycrystalline Si foils has been measured over the energy range 0.1-3.3 MeV per nucleon. For the low energy interval (0.1-0.5 MeV per nucleon), time of flight-energy elastic recoil detection analysis method was used, whilst for the high energy region (1.2-3.3 MeV per nucleon) the energy loss in the same foil was measured using a Si p-i-n diode with the Si-28 ions directly incident on the foil following acceleration. Below the stopping maximum the results are in good agreement with literature data based on Doppler shift measurements of short nuclear lifetimes but are about 20%, smaller than the SRIM prediction. Above the stopping maximum the data are in agreement with SRIM within the limits of statistical uncertainty. (Less)

Measurement and uncertainties of energy loss in silicon over a wide Z1 range using time of flight detector telescopes

The energy loss of projectiles with Z(1) in the range 3-26 has been experimentally measured in the 0.1-0.7 MeV per nucleon energy range in the same Si stopping foil of 105.5 mug cm(-2) thickness using a time of flight-energy (ToF-E) elastic recoil detection analysis (ERDA) setup. A detailed study of the experimental uncertainties for ToF-E and ToF-ToF-E configuration has been made. For ERDA configurations where the energy calibration is taken against the edge positions small uncertainties in the angle at which recoils are detected can introduce significant, absolute uncertainty. The relative uncertainty contribution is dominated by the energy calibration of the Si E detector for the ToF-E configuration and the position of the second ToF detector in ToF-ToF-E measurements. The much smaller calibration uncertainty for ToF-ToF-E configuration implies this technique is superior to ToF-E measurements with Si E detectors. At low energies the effect of charge changing in the time detector foils can become important. It was found that empirical stopping numbers which include the effect of effective-charge were more closely clustered about a trend line when plotted against the Bohr parameter than the corresponding Bethe parameter. Study of the deviations from the trend line showed evidence of a shell dependant effect that exceeded the anticipated maximum relative uncertainties. (Less)

The properties of GaN films grown by plasma assisted laser-induced chemical vapour deposition, and the influence of heavy ion irradiation

GaN has been grown by plasma assisted laser-induced chemical vapour deposition on sapphire and silicon substrates. The optical and morphological properties of the films are described. The films as grown exhibit a high resistivity. The stoichiometry of the films was determined with elastic recoil detection using 200 MeV Au ions as incident beam. Sample modifications induced by the Au beam have been found to increase conductivity. Similar changes occurred when the films were exposed to ultraviolet light.

Heavy-ion elastic-recoil detection analysis of doped-silica films for integrated photonics

Abstract Photosensitive Ge- and Sn-doped silica films are being developed for integrated photonics applications. Such films can be deposited by plasma assisted deposition techniques and their initial refractive index and photosensitivity are determined by the Ge(Sn):Si:O stoichiometry. The presence of H in the films is detrimental to their performance because it causes optical absorption in the 1.3–1.5 μm wavelength range of interest for telecommunications. Characterization of the films therefore requires accurate determination of the film composition, including the presence of H. Heavy-ion elastic-recoil detection (ERD) is shown to provide such information in a single measurement.

Heavy ion ERD of nitrides with a position-sensitive gas ionization detector

A gas ionization detector with novel design features has been developed for the compositional depth-profiling of materials with Elastic Recoil Detection (ERD) using very heavy incident beams. The detector features a large solid angle and thus has high detection efficiency. The detection of the ion position using a saw-tooth ΔE electrode within the anode is energy and species independent and enables the correction of kinematic energy broadening. The energy information is obtained from a single grid-electrode, which considerably simplifies data analysis. All chemical elements, including hydrogen, can be detected simultaneously with similar sensitivity. While it is versatile and applicable to many materials, the technique has unique capabilities when applied to thin films containing carbon, nitrogen or oxygen in combination with heavier elements and hydrogen. In contrast to other techniques, heavy ion ERD resolves all elements in a single measurement and the experimental uncertainty is limited only by counti...