Kameswara Rao

Design and fabrication of liquid phase epitaxy system

The design and fabrication of a simple and versatile liquid phase epitaxial (LPE) system has been described. The present LPE system makes use of the horizontal multi-bin boat and slider arrangement which enables the growth of even multilayered structures. The growth chamber is heated by a single-zone resistive furnace precisely controlled through a Eurotherm 902P temperature programmer and controller. The vacuum manifolds and accessories are set up in such a way as to ensure high vacuum needed for growth experiments. The provision is also made to admit high purity gases like hydrogen or nitrogen into the growth chamber. The design has been kept simple without sacrificing the versatility and adaptability for novel growth experiments. The typical films grown by this LPE system are also presented.

The effect of temperature gradient and ampoule velocity on the composition and other properties of Bridgman-grown indium antimonide

Abstract A systematic study of the role of the melt–solid interface position in determining the crystal quality of Bridgman-grown indium antimonide ingots is made. The crystals are grown under various conditions of imposed gradients and velocities. The gradient-to-velocity ratio Λ in the crystal is seen to move the interface position above or below the melting-point isotherm and this in turn affects crystal quality and grain structure. Post-growth investigations reveal that the growth takes place under off-stoichiometric conditions, for large as well as for small values of Λ , undesirable for growth of high-quality homogeneous ingots of InSb. However, crystals grown under `near-equilibrium conditions are stoichiometric, show low defect density, improved grain structure and comparatively narrow rocking-curve width, with very high mobility.

Influence of Growth Parameters on the Surface and Interface Quality of Laser Deposited InSb/CdTe Heterostructures

The pulsed laser deposition technique has been employed for the growth of single crystalline oriented films of indium antimonide on bulk cadmium telluride substrates. The films grown during this study were tested for surface quality and interface features, generally prevalent due to film-substrate reactions. The composition of the grown film was found to deviate from that of the target owing to loss of antimony during evaporation, leading to the formation of an interfacial compound. The antimony deficiency in the films was compensated by correcting the target composition. Growth parameters and their effects on these manifestations have been studied. The optimization of these parameters has led to growth of layers with good surface morphology and abrupt interfaces. Efforts have been made to detect the origin of the diffuse interface and to identify the compound resulting at the interface through photoluminescence spectroscopy. Using PL and thermoenergetic calculations for the plausible reactions at the interface, we have ascertained that the interfacial compound is more likely to be In 2 Te 3 .

Influence of deviation from stoichiometry on the photoluminescence in CdTe doped with indium

Low temperature photoluminescence of vacuum and cadmium annealed CdTe:In is reported here. A new peak at ∼ 1·14 eV related to transitions from the conduction band to an acceptor involving a tellurium vacancy has been observed.

Pulsed laser deposition of indium antimonide

Single crystalline oriented films of indium antimonide have been grown on cadmium telluride substrates by the pulsed laser deposition technique. The films were (111) oriented which is the substrate orientation. The composition of the grown films were found to deviate from that of the target owing to loss of antimony during evaporation. This deviation from stoichiometry led to film-substrate reaction, resulting in mixed interface. The antimony deficiency in the films were controlled by correcting the stoichiometry, which led to avoiding mixed interfaces. The stoichiometric films showed good surface morphology and well defined sharp interfaces. The IR transmission spectrum showed sharp band to band absorption and effective detection in the MWIR.

Fine structure in 1.4 eV luminescence band from plasma deposited amorphous silicon layers on silicon substrates

Fine structure has been observed in the 1.4 eV luminescence band of thin (≊100 A) amorphous silicon (a‐Si:H) layers deposited on silicon substrates. The energy separation between the peaks is ≊20 meV. A similar luminescence band observed in layers grown on glass substrates under the same conditions is several orders of magnitude lower in intensity and is without perceptible fine structure. There is no change in the nature of the fine structure and the peak energies in films deposited at different substrate temperatures (150–300u2009°C). The dependence of the luminescence band on illumination intensity and on temperature has also been measured. This indicates probable excitonic nature of the luminescence. Possible causes for the observed phenomena are discussed.

Defect mapping system for optoelectronic materials

The defect mapping system is built on the principle of Scanning Optical Microscope (SOM). Its essentially an optical probe with an xY translational stage and a Data Acquisition System (DAS). The SOM can be used in three different modes namely Reflection Transmission and Light Beam Induced Current (LBIC). In this paper the instrumentation and its capability as SOM and in LBIC mode has been demonstrated. I