• D N Bose

      Articles written in Bulletin of Materials Science

    • Deep level transient spectroscopy of anisotropic semiconductor GaTe

      D Pal S Pal D N Bose

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      Deep level transient spectroscopy (DLTS) was carried out on single crystals of the layered chalcogenide p-GaTe using Schottky barriers parallel and perpendicular to the layer planes to study the possible anisotropy of the defect levels. Deep levels with the same energies (0·28 eV and 0·42–0·45eV) have been found in both directions with concentrations ranging from 1013cm−3 to 1014 cm−3 and capture cross-sections from 10−15cm2 to 10−17cm2. The difference in the spectra obtained from the two planes and the possible reason for the deep level energies being independent of crystal orientation are discussed.

    • Optimization of growth of InGaAs/InP quantum wells using photoluminescence and secondary ion mass spectrometry

      S Bhunia P Banerji T K Chaudhuri A R Haldar D N Bose Y Aparna M B Chettri B R Chakraborty

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      InGaAs/InP quantum wells of widths varying from 19 Å to 150 Å have been grown by MOVPE and the growth temperature optimized using photoluminescence and SIMS. It was thus found that for a 78 Å well the lowest PL linewidth of 12.7 meV at 12 K was obtained for growth at 625°C. SIMS also showed sharpest interfaces for this temperature compared with growth at 610°C and 640°C. The well widths determined from PL energies were in good agreement with a growth rate of 8.25 Å/s. However, while the barrier widths of 150 Å were in agreement with SIMS results, the well widths from SIMS were found to be much larger, due to a lower sputtering rate of InGaAs compared with InP. Quantitative comparison was made assuming the presence of InAsP and InGaAsP interface layers on either side of the wells and the relative sputtering rates determined.

    • High resistivity In-doped ZnTe: electrical and optical properties

      D N Bose S Bhunia

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      Semi-insulating < 111 > ZnTe prepared by In doping during Bridgman growth was found to have a resistivity of 5.74 × 107 ohm-cm, the highest reported so far in ZnTe, with hole concentration of 2.4 × 109/cm3 and hole mobility of 46 cm2/V.s at 300 K. The optical band gap was 2.06 eV at 293 K compared with 2.26 eV for undoped semiconducting ZnTe. Thermally stimulated current (TSC) studies revealed 2 trap levels at depths of 202–222 meV and 412–419 meV, respectively. Photoluminescence (PL) studies at 10 K showed strong peaks at 1.37 eV and 1.03 eV with a weak shoulder at 1.43 eV. Short anneal for 3 min at 250°C led to conversion to a 𝑝-type material with resistivity, 14.5 ohm-cm, indicating metastable behaviour. Raman studies carried out on undoped and In-doped samples showed small but significant differences. Possible models for semi-insulating behaviour and meta-stability are proposed.

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