A.B. Maity

Optical properties of ZnxCd1 − xSe films

Abstract Zn x Cd 1−x Se films (0 E g ) in the Zn x Cd 1−x Se films showed a bowing effect, with a bowing parameter of about 1.26. Microstructural information was obtained from X-ray diffraction and transmission electron microscopy (TEM) measurements, which indicated a predominant wurtzite structure for x x > 0.7. The grain size, determined from scanning electron microscopy and TEM, was observed to decrease with increasing zinc content in the films. The films were highly resistive and polycrystalline in nature, with partially depleted grains. An optical method, developed on the basis of the model of Dow and Redfield. was used to determine the barrier height and the density of trap states at the grain boundary region, along with the carrier concentration of the polycrystalline films. The variation of the electric field within the grains also was studied. The effective mass of the carriers varied with x and indicated a bowing effect.

Nanocrystalline diamond films deposited by high pressure sputtering of vitreous carbon

Abstract Nano-diamond films were deposited at room temperature (≈ 300 K) on quartz, Si and Mo substrates by high pressure (≥ 45 mTorr) dc magnetron sputtering of vitreous carbon target in an argon + hydrogen (0–10 vol%) plasma. The nanocrystallites of diamond were embedded in a-C matrix and the ratio of sp3 and sp2 bonds in the film (determined from FTIR) was dependent on the deposition conditions. Formation of nanocrystallites was examined by TEM and SAD patterns. XRD and Raman spectroscopy were also used to probe the microstructural characteristics of the deposited films having average grain size ≈ 55 nm on quartz and ≈ 75 nm on Si and Mo substrates. The films had a surface roughness of ≈ 9 nm on quartz substrates. The sp3 content of the film was high (> 80%) leading to a high band gap (Eg ≈ 4.2 eV) and hardness (Hv≈ 30 GPa). Eg and Hv increased to 5 eV and 50 GPa respectively with the addition of hydrogen (≈10 vol%) in the sputtering environment.

Nanostructured ZnTe films prepared by D.C. magnetron sputtering

Abstract ZnTe films in nanostructured form have been deposited by high pressure d.c. magnetron sputtering of a ZnTe target onto different substrates kept at various temperatures ranging from 223–373 K. Shift of the band gap to higher energies depended on the relative magnitudes of substrate temperature and gas pressure during deposition.

Absorption tail of polycrystalline semiconductor films

Abstract A comprehensive description of the broadening of the absorption tail in polycrystalline semiconductor films has been presented by considering intrinsic inhomogeneity due to random distribution of grains and grain boundary regions and the fluctuation in potential from local thermal vibrations present at the grains and grain-grain interfaces. The model has been applied to describe the absorption data of a number of polycrystalline films. The results of the analysis on CdSe and ZnTe, prepared by hot wall evaporation, and on diamond films, prepared by plasma deposition of acetylene and hydrogen, are presented here.

Stress and microhardness in polycrystalline thin films from below-band-gap absorption studies

A comprehensive model has been developed for the determination of the strain, stress and microhardness of polycrystalline thin films from the below-band-gap optical absorption data which reflect the defect states at the grain boundary regions. The model has been applied to describe the absorption data of AlN and diamond films and consequent interpretation of the mechanical properties of the same is presented.

Photoconductivity of CdTe films

Abstract CdTe films were deposited at different substrate temperatures (423–573 K) using the hot wall evaporation technique. The films were polycrystalline in nature with varying grain size (0.06-0.18 μm). Dark and photo-conductivities in the films were measured in the temperature range 90–300 K. The conductivity data at low temperatures ( 155 K) was explained by the possible thermionic emission of the carrier over the grain boundary potential barrier. The influence of the modulated grain boundary barrier height (at high temperature) and width (at low temperature) with different illumination levels could explain the overall conductivity of CdTe films.

Au/CdS Schottky Diode Fabricated with Nanocrystalline CdS Layer

Schottky diodes of structure Au/nano-CdS/CBD-CdS/SnO 2 were fabricated with the nanocrystalline CdS layer deposited by the high pressure magnetron sputtering technique. The devices were characterized by current-voltage (I-V) anti capacitance-voltage (C-V) measurements. It was observed that the presence of a large amount of surface states might explain the high values of n in the nano-devices. The quantization effects of the active nano-CdS layer in the devices was confirmed from the observed peaks in the plot of conductance versus reverse bias voltage.

Electrical conductivity of nanostructured ZnTe films

Abstract Nanostructured ZnTe films have been deposited by high pressure d.c. magnetron sputtering onto glass substrates. The variation of electrical conductivity with temperature was measured in the temperature range of 100–300 K. The conductivity is found to vary as T − 1 2 within a temperature range 100–150 K, indicating variable range hopping within a Coulomb gap.

NANOCRYSTALLINE ZnSe FILMS PREPARED BY HIGH PRESSURE MAGNETRON SPUTTERING

Abstract Nanocrystalline ZnSe films were deposited onto glass, quartz and NaCl substrates by sputtering of a ZnSe target in argon plasma. Optical, microstructural, and photoluminescence studies were carried out in order to understand the quantization effect, along with optical absorption and emission processes, in the material in nanocrystalline form.

Effect of Ga incorporation in polycrystalline CulnSe2 films

CuIn 1-x Ga x Se 2 (0 ≤ x ≤ 0.25) films were deposited (on glass substrates at ∼770 K) by four source coevaporation technique. The thickness and average grain size of the films varied within 3-3.5 μm and 0.2-0.5 μm, respectively, with small variation of surface roughness (18-24 nm). The films were characterized by measuring the microstructural, optical and mechanical properties. A new optical technique was used to estimate the strain/stress in the polycrystalline films from the broadening of the optical absorption band tail. Addition of Ga increased the stress from 1.37 x 10 8 to 2.78 x 10 8 dynes/cm 2 while the density of trap states (Q t ) at the grain boundaries varied from 7.2 x 10 9 to 1.3 x 10 11 cm -2 . The corresponding variation in the average built electric field (F av ) at the grain-surfaces of the polycrystalline films was estimated to be 0.15-2.95x10 4 V/cm. Surface photovoltage (SPV) measurements of CuIn 1-x Ga x Se 2 /CdS devices indicated minority carrier diffusion lengths (L n ) to be ∼1 μm and 0.7 μm, respectively, for x=0 and x=0.25.