H. L. Hwang

Growth and Properties of Sputter-Deposited CuInS2 Thin Films

Abstract Single-phase CuInS 2 thin films were prepared by r.f. sputtering. The asdeposited films were p type with resistivities in the range 10 −1 −10 1 ω cm . X-ray and electron diffraction data are discussed. Rutherford backscattering and atomic absorption were used for analysis of the composition and the impurities in the thin films. Both the growth direction and the composition of the thin films could be varied by increasing the sulphur vapour pressure during sputtering. Grain size and resistivity data and the effects of post-deposition annealing are also presented.

On the growth of CuInS2 thin films by three-source evaporation

CuInS2 thin films were prepared by three-source evaporation. Special features of the system design are described. The material characterization by compositional, photoluminescence and electrical analyses are reported. Both p and n films were produced: the resistivities were between 0.01 and 10 ω cm, the grain size was between 2 and 8 Ωm, the best electron mobility was 21.84 cm2 V−1 s−1 and the best hole mobility was 1.42 cm2 V−1 s−1. Both of the latter values are higher than those reported with other methods.

Photoreflectance of sulfur‐annealed copper indium disulfide

The temperature dependence of the energy gaps for sulfur‐annealed copper indium disulfide has been studied by photoreflectance in the temperature range of 10–300 K. The sulfur‐annealed sample has been found to have larger transition energies, smaller positive temperature coefficients of energy gaps, and larger spin‐orbit splitting energy than the as‐grown sample. This can be explained by the reduction of d‐level contributions in the upper valence band probably caused by the variation of lattice distance due to native defects.

Microstructures of low‐temperature‐deposited polycrystalline silicon with micrometer grains

The microstructures of low‐temperature polycrystalline silicon grown both on SiO2 and Corning 7059 glass substrate are presented. The silicon was deposited by the hydrogen dilution method using electron‐cyclotron‐resonance chemical‐vapor deposition at 250 °C without any thermal annealing. The hydrogen dilution ratios were varied from 90% to 99%. Transmission electron microscopy images, Raman shift spectra, and x‐ray‐diffraction (XRD) patterns of the films were obtained. The maximum grain size was about 1 μm and the crystalline fraction which was characterized from Raman shift spectra was near 100%. From the XRD patterns 〈111〉‐ and 〈110〉‐oriented crystalline silicon grains were clearly present in the polycrystalline silicon films.

Some remarks on annealing and doping in CuInS2

This paper addresses problems associated with thermal annealing and n‐type and p‐type doping in CuInS2. The results of incorporating impurities like Zn and P in CuInS2 single crystals by different methods are reported. Some evidence has been provided to explain the formation of precipitates being the limiting factor to exhibit the shallow acceptor property. The electron beam annealing of phosphorus‐implanted CuInS2 has been shown for the first time to be an effective way for p‐type conductivity control by extrinsic impurities in any I‐III‐VI2 ternary chalcopyrite.

Pulsed electron beam annealing of phosphorus‐implanted CuInS2

Pulsed electron beam annealing of phosphorus‐implanted CuInS2 has been found to be an efficient method in p‐type doping of CuInS2. A sheet resistance as low as 10.1 Ω/⧠, a sheet carrier concentration as high as 2.6×1016 cm−2, and a hole mobility as high as 499 cm2/V s have been obtained. The irradiation energy density for the best doping condition was determined to be in the range ∼11–13 J/cm2. Using Van der Pauw/Hall technique in conjunction with a chemical etching technique, effective carrier concentration profiles have been determined with a maximum carrier concentration of 9×1019 cm−3. Excellent p‐n CuInS2 homojunctions have been fabricated by electron beam pulse annealing with an ideality factor of 1.75.

Composition determination of CuInS2 by a chemical analysis method

Abstract A chemical analysis method has been developed for the determination of elemental compositions of CuInS 2 in the form of both synthesized charges and single crystals. This method virtually eliminates interference effects among the constituent elements which hinders the precise determination. The results were used to monitor the processes of material synthesis and crystal growth. Homogeneous ingots of CuInS 2 could be obtained and the compositions of CVT grown crystals could be controllably varied. The electrical conductivities were correlated with the compositions of the grown crystals.

Sulfurization of SiO2 surface for polycrystalline silicon growth on SiO2/Si structure at 250 °C

A study of sulfurizing SiO2 surfaces for the growth of Si/SiO2/Si structures was done in the present work. The silicon film was deposited at 250 °C by plasma enhanced chemical vapor deposition. All of the deposited Si films with or without sulfur treatment were of amorphous phases with a H2/(SiH4+H2) flow ratio less than 92%. For those films deposited at the H2/(SiH4+H2) flow ratio of 92%, a transition amorphous Si layer appeared between the SiO2 and polycrystalline silicon films in those samples without sulfur treatment. No transition amorphous Si layer was present in the sample deposited with sulfur treatment, and the largest grain size of polycrystalline silicon was estimated to be around 500 A. The polycrystalline phase was obtained in all the silicon films deposited on SiO2/Si substrate with a H2/(SiH4+H2) flow ratio larger than 92%. This technique would be applicable towards thin film transistor fabrication.

Defect depth profiling using photoluminescence and cathodoluminescence spectroscopy : the role of oxygen on reactive ion beam etching of GaN in O2/Ar plasmas

Abstract This work investigates reactive ion beam etching processes of GaN in O 2 /Ar plasmas and examines the electrical behavior of Schottky diodes fabricated on O 2 /Ar plasmas reactive ion beam (RIB) etched samples. To explore the role that the oxygen plasma plays on the etched GaN, photoluminescence and depth-resolved cathodoluminescence are applied to elucidate the defect relative yellow luminescence. The observation of oxygen-content-dependent defects that are associated with the yellow band has important consequences for our understanding of defect-related luminescence in GaN.

Nonvolatile polycrystalline silicon thin film transistor memory using silicon-rich silicon nitride as charge storage layer

In this work, the authors report a memory device based on a Si thin film transistor (TFT) structure by incorporating silicon-rich silicon nitride (SRSN) film in the gate dielectric stacks as the charge storage layer. The SRSN film has a lower barrier for hole injection than the barrier for electron injection. Therefore, the memory window is dominated by hole injection. The memory window for TFT nonvolatile memory at steady state as large as 6.8V is observed, and the memory window is around 3V under pulse operation. In addition, this TFT memory has no significant degradation after 500 times of switching operation.