Physics

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An isothermal spectroscopic technique called time analyzed transient spectroscopy (TATS) in the constant capacitance (CC) mode has been used to characterize electrically active defects in the MeV Ar+ implanted silicon. The problems associated with high defect density and the presence of damaged region in the as-implanted material are overcome by CC-TATS method. The CC-TATS spectra of the as-implanted sample shows two positive peaks and an attendant negative peak. Two distinct traps have also been identified using thermally stimulated capacitance method modified to operate in constant capacitance mode. Variable pulse width measurements using CC-TATS show exponential capture kinetics in contrast to extremely slow capture observed in conventional deep level transient spectroscopy (DLTS) experiment. The results indicate that trapping behaviour is due to point-like defects associated with extended defects such as dislocation and stacking fault.

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(SoNS) School of Natural Sciences

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Bulletin of Materials Science

Characterization of deep level defects in Si irradiated with Me V Ar + ions using constant capacitance time analyzed transient spectroscopy

The copper germanide phase Cu3Ge which is emerging as an alternative material for making contacts and interconnects for semiconductor industry has been produced across the interface of Cu/Ge bilayers by ion beam mixing at room temperature using 1 Me V Ar ions. The dose dependence of the thickness of the mixed region shows a diffusion controlled mixing process. The experimental mixing rate and efficiency for this phase are 5.35 nm4 and 10.85 nm5keV respectively. At doses above 8 × 1015 Ar/cm2 the formation and growth of another copper rich phase Cu5Ge has been observed. The present theoretical models are inadequate to explain the observed experimental mixing rate.

Ar ion induced copper germanide phase formation at room temperature

In view of the ever-growing importance of ion beams in optical material processing, this letter reports room-temperature MeV He+ ion irradiation induced depletion of hydrogen from single crystalline potassium dihydrogen phosphate (KH2PO4 or KDP) which has wide applications as a nonlinear optical material in optoelectronics technology. Irradiations have been performed using 1.5 MeV He+ ions up to a maximum dose of 2.4 × 1015 ions/cm2. Simultaneously, hydrogen profiling has been done by detecting the elastically recoiled H atoms. Bare KDP crystals show a hydrogen loss of 72% at the maximum dose whereas Au coated samples show that 60 Å of Au layer acts as a barrier to considerably reduce hydrogen depletion from KDP. A possible explanation of these phenomena is suggested.

Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms

Hydrogen depletion from KH2PO4 under He+ ion bombardment

We have studied electrically active defects in buried layers, produced by heavy ion implantation in silicon, using both conventional deep level transient spectroscopy (DLTS) and an isothermal spectroscopic technique called time analyzed transient spectroscopy operated in constant capacitance mode (CC-TATS). We show that CC-TATS is a more reliable method than DLTS for characterization of the heavily damaged buried layers. The major trap produced in the buried layers in p-type Si by MeV Ar+ implantation is found to have an energy level at Ev+0.52 eV. This trap, believed to be responsible for compensation in the damaged layer, shows exponential capture dynamics. We observed an unusually high thermal activation energy for capture, which is attributed to a macroscopic energy barrier for carriers to reach the buried layer. We observe two other majority carrier traps, and also a minority carrier trap possibly due to inversion within the depletion layer. © 1997 American Institute of Physics.

Journal of Applied Physics

Electrically active defects in as-implanted, deep buried layers in p-type silicon

Taking into consideration that the Fock space of a parabose oscillator may be described by bilinear commutation relations involving creation and annihilation operators, we construct the coherent states for odd and even order parabosons.

Journal of Physics A: Mathematical and General

Coherent states for parabosons

We discuss in detail the parasupersymmetric quantum mechanics of arbitrary order where the parasupersymmetry is between the normal bosons and those corresponding to the truncated harmonic oscillator. We show that even though the parasusy algebra is different from that of the usual parasusy quantum mechanics, still the consequences of the two are identical. We further show that the parasupersymmetric quantum mechanics of arbitrary order p can also be rewritten in terms of p supercharges (i.e. all of which obey Qi2 = O). However, the Hamiltonian cannot be expressed in a simple form in terms of the p supercharges except in a special case. A model of conformal parasupersymmetry is also discussed and it is shown that in this case, the p supercharges, the p conformal supercharges along with Hamiltonian H, conformal generator K and dilatation generator D form a closed algebra.

Pramana - Journal of Physics

Truncated harmonic oscillator and parasupersymmetric quantum mechanics

Using techniques of supersymmetric quantum mechanics we derive phase equivalent partner potentials to Eckart and Bargmann potentials. It is found that the partner potentials pick up new singularities which are absent in the parent potentials.

Modern Physics Letters A

New phase equivalent partners to Eckart and Bargmann potentials

Quasi-exactly solvable rational potentials with known zero-energy solutions of the Schrödinger equation are constructed by starting from exactly solvable potentials for which the Schrödinger equation admits an so(2,1) potential algebra. For some of them, the zero-energy wave function is shown to be normalizable and to describe a bound state. © 1997 Elsevier Science B.V.

Physics Letters, Section A: General, Atomic and Solid State Physics

Zero-energy states for a class of quasi-exactly solvable rational potentials

Damage induced by MeV Ar+ ion implantation and end of range defects in Si have been studied by capacitance-voltage, thermally stimulated capacitance, deep level transient spectroscopy (DLTS) and time analyzed transient spectroscopy (TATS). Unlike earlier studies, which focus on defects induced during post-implantation annealing steps, we study as-implanted p-type silicon samples. We report the occurrence of mid-gap acceptor levels using DLTS and TATS in a region well beyond the ion range. The presence of temperature dependent series resistance due to damaged region distorts DLTS lineshapes, even leading to sign reversal of DLTS peaks in some cases. A new and better method of correcting series resistance effects in capacitance transients has been employed. It is based on detecting the point of inversion of isothermal transients which are nonmonotonic due to the presence of series resistance. The capture process is found to be thermally activated with a high barrier energy. Possible origin of capture barrier and broadening in activation energy are discussed. Our results indicate that these deep levels are associated with point defects with local disorder in the neighbourhood.

Electrically active defects due to end-of-ion-range damage in silicon irradiated with MeV Ar+ ions

We point out a supersymmetric generalization of Ito's coupled KdV equation which possesses infinite conservation laws and associated symmetries.