N. Zafar

Characterization of deep levels introduced by alpha radiation in n‐type silicon

A detailed deep‐level transient spectroscopy study of the characteristics of deep‐level defects introduced by 5.48 MeV alpha particles in low‐doped n‐Si is reported. The deep‐level characteristics studied include emission rate signatures, activation energies, capture cross sections and their temperature dependence, and defect concentrations and their spatial profiles. At least five deep levels in the upper‐half band gap and two levels in the lower‐half gap have been observed as a result of irradiation and characterized in detail. A systematic study of their generation rates up to a dose of about 3×1010 alpha particles/cm2 has been performed providing insights into the dose dependence of their formation mechanisms. Interesting room temperature transformation phenomena have been observed in our deep‐level spectra during room temperature storage of the irradiated samples. Extensive isochronal thermal annealing measurements have been carried out to obtain data on the anneal‐out characteristics of the radiatio...

Study of alpha‐radiation‐induced deep levels in p‐type silicon

Deep levels introduced by 5.48 MeV alpha particles in p‐type silicon have been studied using deep‐level transient spectroscopy. The generation rates of these defects have been obtained up to a dose of 1.2×1011 α particles/cm2. Detailed data have been obtained on the electrical characteristics of the two deep levels in the lower‐half band gap at Ev+0.21 eV and Ev+0.35 eV and one level in the upper‐half gap of silicon at Ec−0.25 eV introduced by irradiation. These characteristics include emission rate signatures, carrier capture cross sections, and their temperature dependence and deep‐level concentrations. Detailed isochronal annealing measurements have been performed to obtain data on the annealing behavior of the deep‐level defects and also to help identify these centers. Some interesting phenomena relating to temporal changes in our deep level spectra stimulated by minority carrier injection have been observed and discussed in the light of the available literature on radiation‐induced defects in silicon.

Palladium-related deep levels in silicon

The results of a study carried out on Pd-doped p+n Si junctions using deep-level transient spectroscopy (DLTS) are reported. Four deep levels associated with Pd at energy positions Ec-0.18 eV, Ec-0.22 eV, Ec -0.37 eV and Ec-0.59 eV are observed. These deep levels have been observed simultaneously in the same as-diffused Si:Pd samples for the first time, to the best of the authors knowledge. Detailed data on the emission rates, capture cross sections and their temperature dependence and deep-level distribution profiles of the palladium-related defects are presented. Isochronal annealing characteristics of these defects have also been studied up to 400 degrees C yielding some interesting new insights. The authors results cast doubts on some of the currently held models for the structure of some of these defects.

Characteristics of deep levels associated with rhodium impurity in n-type GaAs

Deep levels have been characterized in n-type GaAs crystalline films grown by metalorganic chemical vapor deposition, doped in situ with 4d transition metal, rhodium, using the deep level transient spectroscopy (DLTS) technique. Two prominent broad bands of deep levels are found to be associated with Rh impurity, one in the upper half and the other in the lower half of the band gap. The band of electron emitting deep levels is shown to extend from 0.57–0.67 eV below the conduction band edge while the hole emitting deep levels band peaks at Ev+0.42 eV. Detailed double-correlation DLTS measurements are performed to investigate the characteristics of the observed Rh-related deep levels. Both deep level bands are found to exhibit significant dependence of the thermal emission rates on the electric field from these measurements. The observed variation of the peak profile with the capture time for the electron emission band and theoretical analysis of the field dependence data support a band-like-extended-defec...

Characteristics of Alpha-Radiation-Induced Deep Level Defects in p-Type InP Grown by Metal-Organic Chemical Vapor Deposition

Room temperature storage and/or minority carrier injection behaviors of three prominent majority carrier levels H3 (Ev+0.34 eV), H4 (Ev+0.39 eV) and H5 (Ev+0.58 eV) and three minority carrier levels, 0.22, 0.29 and 0.35 eV below the conduction band edge in metal-organic chemical vapor deposition (MOCVD) grown p-type InP crystals produced by alpha radiation have been studied using deep levels transient spectroscopy. In particular, H5, absent immediately after irradiation, is found to grow with storage at room temperature after irradiation with no change in the other two majority carrier levels. Minority carrier injection saturates H5 while H3 and H4 continue to decay after injection. These observations are interpreted to mean that H4 and H5 are unrelated levels with no or very little mutual conversion proposed in some previous irradiation studies. Detailed production rate data for H3, H4 and H5 (post-injection) over a range of alpha-particle doses have also been provided for the first time.

Interaction of α‐radiation induced defects with Pd‐related deep levels in silicon

Results of a detailed deep level transient spectroscopy study of Pd‐doped p+n Si diodes irradiated with 5.48 MeV α particles are presented, which also include investigations of isochronal annealing behavior of the deep level spectra up to a temperature of 350–400 °C. An extended comparison with results obtained on reference samples as well as with previously published results of deep level studies on Pd‐doped samples (unirradiated) and on undoped α‐irradiated samples provides valuable information, since the same starting material is used in all these studies. It is observed that, in general, the Pd‐related deep levels increase in concentration upon irradiation at the expense of α‐radiation‐induced levels. In particular, the A center sharply decreases in concentration upon post‐irradiation annealing with a corresponding increase in the concentration of the dominant Pd‐related level. The results also show that, contrary to the previously held belief, two well‐known Pd‐related levels at Ec−0.37 eV and Ec−0.5...

Interaction of iron with transition metals and alpha radiation in thermally quenched p-silicon

Iron-induced deep levels have been studied in p-type silicon quenched from high temperatures, using deep-level transient spectroscopy. The interstitial iron donor and the iron - boron pair defect are observed and identified by a number of their characteristics including their mutual transformation. Our recent work revealed an interesting new property of the interstitial iron donor defect, namely its complete bleaching by the transition metals Ag, Au, Pt and Pd in samples which have received thermal treatment identical to the undoped samples. The study reported here was intended to investigate the relationship of this effect to the well known iron - boron complex defect known to act as a source of the interstitial iron defect by injection-induced dissociation in boron doped p-silicon. Our results show that both the iron - boron complex and the isolated interstitial iron defects disappear concurrently in our transition-metal-doped samples. Thus the bleaching of the iron interstitial in the presence of the transition metals used is found to be associated with the bleaching of this source rather than due to some unknown complex mechanism inhibiting the dissociation of these pairs in the presence of the transition metals. In addition, the response of the iron interstitial defect to irradiation with alpha-particles and its thermal annealing behaviour have been studied. Alpha-irradiation is seen to lead to a significant suppression of the iron interstitial defect, in agreement with the hitherto reported results of electron irradiation, without causing any significant change in its thermal annealing characteristics.

α‐radiation‐induced deep levels in low‐doped n‐type silicon

Observations on deep levels introduced in silicon by α‐particle irradiation are reported. Low‐doped n‐type samples are used and deep level transient spectroscopy is applied to detect the deep levels. Preliminary results provide evidence for some new defect states in addition to those previously reported. The study also reveals interesting metastability and room‐temperature transformation effects associated with some of the deep levels introduced.

Controversy regarding the 0.85‐eV deep hole level in GaP

Thermal emission rate data have been obtained on a 0.85‐eV deep hole level in liquid‐phase‐epitaxial GaP light‐emitting diodes using dark capacitance transients. Published emission rate data on this level exist for vapor‐phase‐epitaxial GaP. Detailed comparison with available data reveals a wide spread in emission rates casting serious doubts on the hitherto presumed origin of this level.

Sensitive thermometry using capacitance variation of GaP leds

Abstract Red-emitting GaP LEDs are shown to provide highly sensitive temperature sensors. This investigation is based on the exploitation of capacitance variation rather than the usually employed forward voltage variation. Detailed results on thermometric characteristics are reported. A temperature variation of as low as 0.02 degree can be reliably sensed using capacitance thermometry.