Sukriti Ghosh

Studies on electron transport properties and the Burstein-Moss shift in indium-doped ZnO films

Abstract Electrical conductivity, Hall mobility, thermoelectric power and optical properties were studied for indium-doped zinc oxide films produced by the magnetron sputtering technique. The data were analysed in the light of the existing theories and it was observed that scattering due to neutral impurities together with optical phonons is operative in these films. The optical data indicated a distinct Burstein-Moss shift. The values of carrier concentration, plasma frequency and optical band gap were correlated with each other, indicating the effective mass of carriers to be equal to 0.35me.

Grain boundary scattering in aluminium-doped ZnO films

Abstract Electrical conductivity and Hall mobility of ZnO:Al films were measured in the temperature range 170–350 K. The effects of post-deposition heat treatment in vacuum and hydrogen atmosphere on the above properties were studied to derive meaningful information on the scattering mechanisms in these films. Grain boundary scattering was found to be the predominant mode of scattering at lower temperatures whereas the contribution from ionized impurities together with phonon scattering become significant at higher temperatures. The density Q t of trap states and its position was determined.

Microstructure of ZnO films produced by reactive DC sputtering technique

Abstract The effect of grain growth of zinc oxide films deposited by using a reactive DC magnetron sputtering technique was studied as a function of annealing temperature. The results are correlated with the observed electrical and optical studies.

Role of hydrogen dilution and diborane doping on the growth mechanism of p‐type microcrystalline silicon films prepared by photochemical vapor deposition

Boron‐doped microcrystalline hydrogenated silicon (μc‐Si:H) films were grown from a gas mixture of silane, diborane, and hydrogen employing mercury sensitized photochemical vapor deposition. At a low diborane doping ratio (1.1×10−3) hydrogen dilution of source gases resulted in films exhibiting a maximum conductivity of 7.4 S cm−1. For a higher doping ratio (10−2) the value of conductivity remained almost unchanged (10−5–10−6 S cm−1) with hydrogen dilution indicating nonexistence of microcrystallinity under such conditions. Transmission electron microscopy of B‐doped μc‐Si:H films revealed formation of crystallites possessing different crystallographic orientations, e.g., (111), (220), and (311) along with other planes. X‐ray spectra confirmed a large number of crystallites with (220) orientations.

Influence of boron doping and hydrogen dilution on p‐type microcrystalline silicon carbide thin films prepared by photochemical vapor deposition

Boron doped μc‐SiC:H films have been prepared by low power (10 mW/cm2) photochemical vapor decomposition of SiH4, C2H2, and B2H6 gases diluted with hydrogen. The effect of boron doping and hydrogen dilution on structural and opto‐electronic properties have been studied. The microstructure consists of Si crystallites while carbon remains at the grain boundaries and amorphous parts. Diborane doping beyond an optimum value has been observed to deteriorate the formation of microcrystallites. By optimizing the process parameters, p‐type μc‐SiC:H having σd∼3.0×10−3 S cm−1 with an E04 of 2.34 eV has been obtained. This film exhibits high optical transmittivity compared to its amorphous counterpart.

Effect of chamber pressure on p-type μc-SiC:H thin films prepared by photo-CVD

Abstract Highly conducting boron-doped microcrystalline silicon carbide ( μ c-SiC:H) thin films have been prepared by mercury sensitised photochemical vapor deposition. The chamber pressure was identified as one of the most crucial parameters governing the microcrystalline growth as well as the dopant incorporation in the microcrystalline thin films. Raman studies show the crystalline size and volume fraction decreases with increasing pressure. Transmission electron microscopy of such films reveal that the crystalline phase contains silicon only, so that carbon is incorporated only in the amorphous phase. The presence of carbon in these films was confirmed by secondary ion mass spectroscopy. There is an optimum pressure (0.5 Torr), depending upon the other deposition parameters, for which the conductivity of p-type μ c-SiC:H film is highest (1.2×10 −4 S cm −1 ).

Microcrystalline silicon carbon alloy film prepared by photo-chemical vapour deposition

Abstract Silicon carbon alloy thin films were prepared by photo-chemical vapour deposition using SiH4 and C2H2 gases, diluted with 97% H2. The effect of chamber pressure on the properties of the film were investigated and are explained from the standpoint of growth mechanism. The 0.4 μm thin film prepared at a pressure of 67 Pa exhibited a dark conductivity of 8.2 × 10−9 S cm−1 along with low optical absorption. The bonded hydrogen content in the film is 6 at.% as estimated from IR spectra. X-ray and electron diffraction study revealed the film to be microcrystalline. The observed crystalline planes are ascribed to crystalline silicon (c-Si), embedded in amorphous silicon carbon (a-SiC:H) tissue. This is also confirmed by the appearance of the TO mode of c-Si at 518 cm−1 in the Raman spectrum. Thus in microcrystalline silicon carbon (μc-SiC) film, the crystallinity is due to silicon alone while carbon is present at grain boundaries and in amorphous regions separating the crystallites. However, the optical absorption of the film is lower than that of μc-Si:H as the absorption is governed by the amorphous part.

An x‐ray diffraction study on the microstructures of cold‐worked face centered cubic Cu–Sn–Zn alloys. II. Role of addition of 1 wt. % Sn

In continuation with our earlier work with Cu–Ni–Zn (Paper I) [Halder, De, and Sen Gupta, J. Appl. Phys. 48, 3560 (1977)], the role of addition of nontransitional solute tin (Sn) in the dilute range (∼1 wt. %) to alpha‐brass alloys having compositions 5.0–34.0 wt. %Zn [present experiment concerns initial range, i.e., 5–24 wt. % Zn, and 24–34 wt. % Zn have been studied earlier by Halder, De, and Sen Gupta, Ind. J. Pure Appl. Phys. 17, 492 (1979)] has been examined in the light of x‐ray diffraction methods of analyses dealing with peak shift, peak asymmetry, and peak broadening. Unlike the binary system, it has been interestingly observed that the addition of solute element tin in near dilute range of 1 wt. % to alpha‐brass system increases the net‐stacking fault concentration initially and has an arresting effect on all the microstructural parameters (namely, deformation stacking faults, coherent domain size, rms strains, density of dislocations, stacking fault energy, etc.), which do not change significan...

Widegap a-Si:H films prepared at low substrate temperature

Abstract Wide bandgap hydrogenated amorphous silicon (a-Si:H) films have been prepared by the PECVD method at a low substrate temperature (80°C) controlling the incorporation of hydrogen (bonded with silicon) into the film. Optimizing the deposition parameters viz. hydrogen dilution, rf power, a-Si:H film with E g ∼ 1.90 eV and σ ph ≥ 10 −4 Scm −1 has been developed. This film exhibited better optoelectronic properties compared to a-SiC:H of similar optical gap. The quantum efficiency measurement on the Schottky barrier solar cell structure showed a definite enhancement of blue response. Surface reaction as well as structural relaxation under suitable deposition condition have been claimed to be responsible for the development of such material.

Hydrogenated amorphous silicon films prepared at high substrate temperature : properties and light induced degradation

Of the different deposition parameters, the substrate temperature Ts has a profound effect on the microstructure and optoelectronic properties of hydrogenated amorphous silicon (a‐Si:H). A detailed study was done to evaluate a‐Si:H materials deposited at high substrate temperatures (≥325 °C). Their characteristics and nature of light induced degradation were compared to a‐Si:H deposited at 200 °C. Electrical properties were studied with coplanar electrode structure as well as on Schottky barrier devices. Absorption measurements in the visible and infrared regions and spin‐density measurements were carried out. For high Ts (≥325 °C) the presence of acceptorlike defects are indicated in addition to the neutral dangling bonds. Annealing recovery from the light soaked state is slower as compared to a film deposited at 200 °C. The results have been discussed in connection with the role of hydrogen motion in the annealing of light induced defects.