Prakash Deenapanray

Doping dependence of the carrier lifetime crossover point upon dissociation of iron- boron pairs in crystalline silicon

The excess carrier density at which the carrier lifetime in crystalline silicon remains unchanged after dissociating iron-boron pairs, known as the crossover point, is reported as a function of the boron dopant concentration. Modeling this doping dependence with the Shockley-Read-Hall model does not require knowledge of the iron concentration and suggests a possible refinement of reported values of the capture cross sections for electrons and holes of the acceptor level of iron-boron pairs. In addition, photoluminescence-based measurements were found to offer some distinct advantages over traditional photoconductance-based techniques in determining recombination parameters from low-injection carrier lifetimes.

Implant isolation of ZnO

We study ion-irradiation-induced electrical isolation in n-type single-crystal ZnO epilayers. Emphasis is given to improving the thermal stability of isolation and obtaining a better understanding of the isolation mechanism. Results show that an increase in the dose of 2 MeV 16O ions (up to ∼2 orders of magnitude above the threshold isolation dose) and irradiation temperature (up to 350 °C) has a relatively minor effect on the thermal stability of electrical isolation, which is limited to temperatures of ∼300–400 °C. An analysis of the temperature dependence of sheet resistance suggests that effective levels associated with irradiation-produced defects are rather shallow (<50 meV). For the case of implantation with keV Cr, Fe, or Ni ions, the evolution of sheet resistance with annealing temperature is consistent with defect-induced isolation, with a relatively minor effect of Cr, Fe, or Ni impurities on the thermal stability of isolation. Results also reveal a negligible ion-beam flux effect in the case o...

Electrical isolation of ZnO by ion bombardment

The evolution of sheet resistance of n-type single-crystal wurtzite ZnO epilayers exposed to bombardment with MeV 1H, 7Li, 16O, and 28Si ions at room temperature is studied in situ. We demonstrate that sheet resistance of ZnO can be increased by about 7 orders of magnitude as a result of ion irradiation. Due to extremely efficient dynamic annealing in ZnO, the ion doses needed for isolation of this material are about 2 orders of magnitude larger than corresponding doses in the case of another wide-bandgap semiconductor, GaN. Results also show that the ion doses necessary for electrical isolation close-to-inversely depend on the number of ion-beam-generated atomic displacements. However, in all the cases studied, defect-induced electrical isolation of ZnO is unstable to rapid thermal annealing at temperatures above ∼300 °C.

Formation rates of iron-acceptor pairs in crystalline silicon

This work has been supported by the Australian Research Council and the State of Lower Saxony.

Suppression of interdiffusion in GaAs/AlGaAs quantum-well structure capped with dielectric films by deposition of gallium oxide

J. Wong-Leung, P. N. K. Deenapanray, and H. H. Tan acknowledge the fellowships awarded by the Australian Research Council.

Deep Level Transient Spectroscopy of Defects in High-Energy Light-Particle Irradiated Si

The authors review what has been learned concerning the electrical and annealing properties of point defects in high-energy electron or proton irradiated Si from deep level transient spectroscopy (DLTS). The authors have focused mainly on the properties of electron traps, and to a lesser extent on the properties of hole traps. In addition to an in-depth discussion of hydrogen-related defects in Si, this review article provides a brief tutorial on ion-solid interactions and the theory underlying DLTS. The authors also provide a few examples of the power of high resolution Laplace DLTS in analyzing radiation induced defects. The collection of results gathered in this article may provide the fundamental information for successful defect engineering in light-particle irradiated Si.

Core-level photoemission and near-edge x-ray absorption fine-structure studies of GaN surface under low-energy ion bombardment

We have investigated compositional changes on GaN surfaces under low-energy Ar ion bombardment using synchrotron-based high-resolution core-level photoemission measurements and near-edge x-ray absorption fine-structure (NEXAFS) spectroscopy. The low-energy ion bombardment of GaN produces a Ga-rich surface layer which transforms into a metallic Ga layer at higher bombarding energies. At the same time, the photoemission spectra around the N 1s core level reveal the presence of both uncoordinated nitrogen and nitrogen interstitials, which we have analyzed in more detail by x-ray absorption measurements at the N K-edge. We have proposed a mechanism for the relocation and loss of nitrogen during ion bombardment, in agreement with some recent experimental and theoretical studies of defect formation in GaN. We have also demonstrated that photoemission spectroscopy and NEXAFS provide a powerful combination for studying compositional changes and the creation of point defects at GaN surface.

The role of oxygen on the stability of gettering of metals to cavities in silicon

The effect of oxygen implanted into epitaxial Si layers on the ability to getter Au to nanocavities, previously formed by H implantation and annealing, has been studied by Rutherford backscattering, transmission electron microscopy, and secondary ion mass spectrometry. We demonstrate that oxygen is gettered to cavities during extended annealing at 950 °C. Furthermore, the arrival of oxygen at cavities is not only shown to inhibit subsequent attempts to getter Au to cavities, but also to eject chemisorbed Au from the cavity walls. Similar behavior is observed in Czochralski Si, where the source of oxygen is within the Si itself.

Investigation of reactive ion etching of dielectrics and Si in CHF3∕O2 or CHF3∕Ar for photovoltaic applications

Using a combination of etch rate, photoconductance, and deep level transient spectroscopy (DLTS) measurements, the authors have investigated the use of reactive ion etching (RIE) of dielectrics and Si in CHF3∕O2 and CHF3∕Ar plasmas for photovoltaic applications. The radio frequency power (rf-power) and gas flow rate dependencies have shown that the addition of either O2 or Ar to CHF3 can be used effectively to change the etch selectivity between SiO2 and Si3N4. The effective carrier lifetime of samples degraded upon exposure to a CHF3-based plasma, reflecting the introduction of recombination centers in the near-surface region. The extent of minority carrier lifetime degradation was similar in both types of plasmas, suggesting that the same defects were responsible for the increased recombination. However, the rf-power dependence of lifetime degradation in n- and p-type Si was different. Moreover, the lifetime degradation did not exhibit a linear rf-power dependence, suggesting that primary defects were n...

Silane flow rate dependence of SiOx cap layer induced impurity free interdiffusion of GaAs/AlGaAs quantum wells

Impurity-free intermixing of GaAs/Al 0.54 Ga 0.46 As quantum wells was carried out using SiO x capping layers grown by plasma enhanced chemical vapor deposition followed by rapid thermal annealing at 950°C. A dependence of quantum well intermixing on the quality of dielectric layer was observed, which was varied by changing the silane flow rate, M (40 sccm ≤ M ≤ 480 sccm). The quality of capping layers were determined using Rutherford backscattering spectroscopy, spectroscopic ellipsometry, secondary ion mass spectrometry, Fourier transform infrared spectroscopy, and P-etch measurements. The porosity and oxygen content of capping layers, and the incorporation of nitrogen during deposition were the main factors influencing the extent of blue shifts achieved in intermixed quantum wells. Substantially higher energy shifts were obtained for capping layers deposited using M < 160 seem Slightly overstoichiometric layers which were relatively more porous but containing less nitrogen were obtained for M < 160 seem For higher silane flow rates substoichiometric oxide layers with increased hydrogen and nitrogen contents were obtained. Our results suggested that the mobility of out-diffusing Ga atoms during annealing was enhanced by film porosity but was suppressed with increasing nitrogen content in the capping layer.