Dislocation Density In Films Research Articles

Cu2ZnSnS4 films with Cu-poor composition prepared by spin coating from a nontoxic methanol-based solution: the effect of annealing temperature

ABSTRACT In comparison with the stoichiometry and Zn-rich/Cu-poor compositions of Cu2ZnSnS4 (CZTS) photovoltaic material, the properties of Cu-poor films have not been explored adequately. In this study, Cu-poor films were spin-coated from a non-hazardous methanol-based solution. Films were subject to a brief annealing process in the temperature range of 350–550 °C. As-grown and annealed films were uniform, compact, photosensitive, and free from secondary phases. As the annealing temperature increased, the size of crystallites increased and the film dislocation density decreased steadily. Films had a direct bandgap of 1.4–1.5 eV. The presence of three sub-bandgap transitions were detected and identified. By varying the annealing temperature, hole concentration, hole mobility, and film resistivity varied systematically in the range of 1016–1018 cm−3, 1–140 cm2/V-s, and 0.02–64 Ωcm, respectively. Cu-poor films showed structural and optoelectronic properties similar to the Zn-rich/Cu-poor and stoichiometric films and, thus, have the potential for device applications.

Effect of Al doping on the microstructural, optical and electrical properties of ZnO films

We prepared Al doped ZnO films by spin coating sol–gel method on ordinary glass substrates. The microstructure of the films was evaluated as a function of doping concentration by X-ray diffraction line broadening analysis using convolutional multiple whole profile fitting method. The optical band gap and activation energy of ZnO films were also determined at different aluminum contents and the correlation between band gap and microstructure was investigated. The following changes were observed, with the rise of doping concentration: the dislocation density of films increases from 9.1 ( 5 ) × 10 14 to 4.1 ( 5 ) × 10 15 m - 2 , volume weighted average domain size decreases from 35(2) to 13(2) nm and the band gap linearly increases from 3.307(7) to 3.358(9) eV.

Improvement in GaN and AlGaN/GaN Schottky diode performance by reduction in epitaxial film dislocation density

The electrical characteristics of AlGaN/GaN heterostructures and GaN Schottky diodes were correlated with dislocations and other material defects. GaN epitaxial films were grown using conventional metal organic chemical vapor deposition (MOCVD) and pendeo-epitaxy, while AlGaN/GaN heterostructures were grown using conventional MOCVD. Current-voltage (I-V) measurements displayed a wide variation in ideality factor and reverse leakage current density. Schottky diodes fabricated on the pendeo-epitaxial material displayed improved ideality factor (n=1.35) and leakage current density measured at −2 V (J=54.5 A/cm2) compared to conventionally grown GaN (n=1.73,J=117 A/cm2). The electrical properties of the Schottky diodes on the AlGaN/GaN heterostructure varied across the sample, showing no spatial dependence. Ideality factor and Schottky barrier height ranged n=1.6−3.0 and ϕB=0.69−0.87, respectively. Reverse leakage current density at −2 V varied by up to three orders of magnitude. Etch pit density and atomic force microscopy revealed three orders of magnitude reduction in dislocation density for the pendeo-epitaxial GaN compared to conventional GaN, while cathodoluminescence indicated lower defect density for the pendeo-epitaxial GaN. Etch pit density revealed almost an order of magnitude lower dislocation density beneath those diodes with improved characteristics on the AlGaN/GaN heterostructure.

Low-temperature chemical-vapor deposition of 3C–SiC films on Si(1 0 0) using SiH 4–C 2H 4–HCl–H 2

The benefits of adding HCl on the low-temperature (1000°C) epitaxial growth of 3C–SiC on Si(1 0 0) were examined. At either silicon rich (C/Si<1) or carbon rich (C/Si>1) inlet gas ratios, the SiC film composition approached stoichiometry by adding HCl, but only at an inlet C/Si ratio of 1 was the composition of the SiC film approximate 1.0 with a Cl/Si input ratio of 50. The structure of the films improved with the addition of HCl, confirmed by both X-ray diffraction and TEM. For epitaxial films, the FWHM of X-ray diffraction rocking curves decreased to 0.37° or 1348 arcs with increasing Cl/Si to 50 at a C/Si ratio of 1. The film dislocation density was reduced from 1.1×10 10 cm −2 for a 2.0 μm thick film for a Cl/Si ratio of 0 to 4.27×10 9 cm −2 for a 0.75 μm thick film at a Cl/Si ratio of 50. The benefits of adding HCl are attributed to the suppression of pure silicon nucleation and the reduction in growth rate.

Te-rich liquid phase epitaxial growth of HgCdTe on Si-based substrates

The growth of high quality (111)B oriented HgCdTe layers on CdZnTe/GaAs/Si and CdTe/Si substrates by Te-rich slider liquid phase epitaxy (LPE) is reported. Although the (111) orientation is susceptible to twinning, a reproducible process yielding twin-free layers with excellent surface morphology has been developed. The electrical properties and dislocation density in films grown on these substrates are comparable to those measured in HgCdTe layers grown on bulk CdTe substrates using the same LPE process. This is surprising in view of the large lattice mismatch that exists in these systems. We will report details of both the substrate and HgCdTe growth processes that are important to obtaining these results.

Effects of Defects on Metal-Insulator-Semiconductor Properties of HgCdTe Films Grown by Liquid Phase Epitaxy

ABSTRACTA comprehensive study of all materials parameters influencing metal-insulator-semiconductor (MIS) properties of n-type HgCdTe films grown by liquid phase epitaxy from tellurium rich melts was conducted. When the epitaxy process was optimized to grow films free of inclusions and terracing, the first indications of the MIS properties to be expected could be obtained from the temperature dependence of the Hall electron mobility.Films displaying an anomalous dependence of the Hall mobility on temperature yielded non-classical low frequency MIS properties with little or no measurable ‘dark’ storage times (&lt; 2×10−6 second). The MIS performance of these films appeared relatively independent of other materials parameters; remaining, for example, virtually unaffected by the film dislocation density changing between 5×104 and 2 × 106/cm2.Films displaying a classical dependence of the Hall mobility on temperature yielded drastically improved classical high frequency MIS properties. For these films, the MIS performance appeared almost exclusively dependent on dislocation density levels as long as the donor density remained lower than 1×1015/cm3. The dark storage time of classical films increased continuously with decreasing dislocation density levels, rising to 100µsec for a dislocation density level of 1 × 105/cm2 for materials with a 77°K cutoff wavelength of 10.5 µm. A simple monotonic relationship could be established between the MIS performance parameters and the dislocation density over the entire measurement span: from 5×104 to 2.5×106/cm2.

Growth of dislocation-free silicon films by molecular beam epitaxy (MBE)

The dependence of dislocation density on various growth conditions for Si MBE films is investigated. Dislocation density is determined by chemical etching and SEM observation. High temperature heat treatment generates dislocations in substrates, and film dislocation density increases with an increase in the substrate dislocation density. The dislocation generation in the substrate is prevented by using a substrate heater designed not to induce thermal stress. The film dislocation density decreases exponentially with an increase in the preheating time of the substrate. The density is proportional to exp (E/kBT) where T is growth temperature. The value of the activation energy is 3.5 eV. Dislocation-free films can be grown reproducibly at 860 °C on (100)-oriented substrates preheated to 1210 °C for 10–20 min.

Structure perfection of some molecular crystals grown from the melt

AbstractSingle crystals of anthracene, naphthalene, phenazine and anthracene sym. trinitrobenzene (TNB) were examined using X‐ray topography. Low‐angle boundaries were observed and misorientation vectors of adjacent mosaic blocks have been estimated. Using an X‐ray camera with oscillating film dislocation density in crystals has been evaluated. Anthracene‐TNB crystals showed a much higher structure perfection than the other crystals.

Galvanomagnetic properties of recrystallized dendritic InSb films

The galvanomagnetic properties of monophase, dendritic, preferentially oriented InSb films grown from a non-stoichiometric melt containing an excess of Sb, are described. Such films are n-type and have the following properties: a Hall coefficient of the same order of magnitude as that of bulk polycrystalline InSb, an electron mobility which is thickness dependent reaching a value μ e = 4 × 10 4 cm 2/V-sec in films 3 μm thick, a magnetoresistance which is quadratic in H for μH < 1 and is linear in H for μH > 1, inhomogeneity fluctuations and resistivity striations which lead to geometrical effects larger than those associated with macroscopic length to width ratios of rectangular specimens. The charge carrier density in these films is between 5 × 10 16 electrons/cm 3 and 2 × 10 16 electrons/cm 3 near 300°K. Experimental data suggests that lattice scattering, in combination with dislocation scattering in accordance with the Dexter-Seitz model, accounts for the temperature dependence of the electron mobility above 200°K. Calculated dislocation densities in films are of the order of 10 9. It is suggested that dislocation scattering represents a significant mobility limiting process in evaporated or recrystallized InSb films.