Keiji Maeda

Observation of dislocations in cadmium telluride by cathodoluminescence microscopy

A one‐to‐one correspondence between deformation‐produced dark spots in cathodoluminescence (CL) micrographs and dislocations has been demonstrated in n‐type CdTe by comparing the CL pattern with the etch‐pit pattern developed with a new etchant which has been ascertained to reveal dislocations by a successive polishing and etching method.

Stacking-fault energy of II–VI compounds

Abstract Stacking-fault energies on the {111} plane in ZnTe (zinc blende structure) and on the (0001) plane in ZnO (wurtzite structure) have been estimated to be 16 ± 4 and greater than 43 mJ m−2, respectively, by weak-beam electron microscopy of dislocations. The stacking-fault energies of the above crystals and previously obtained ones of other II-VI compounds, CdTe, CdS, CdSe, ZnSe and ZnS, are correlated with material parameters such as the ionicity of the crystal. It is found that the stacking-fault energies of II-VI compounds, together with those of six III-V compounds so far reported, show a strong correlation with the charge redistribution indices found by Phillips end Van Vechten (1969). The physical implication of the correlation is discussed.

Nonideal J-V characteristics and interface states of an a-Si:H Schottky barrier

A new theory is developed for nonideal J‐V characteristics of Schottky barriers with an interfacial layer. This theory is based on the model that nonideal characteristics are due to changes of population in the interface states under applied bias and accompanying changes of the barrier height. The population in the interface states is expressed by the Fermi level, which can be determined by analyzing experimental results. The J‐V characteristics are obtained from the flow of carriers into and out of the interface. Tunneling through the interfacial layer constitutes the bottleneck for the carrier flow. Under forward bias, the carrier concentration ns at the interface is proved to be in thermal equilibrium with the bulk. Under reverse bias, ns is in local thermal equilibrium with the interface states. This theory is applied to an undoped a‐Si:H Schottky barrier without introducing any ambiguous quantities. The experimental ideality factor, its dependence on temperature and voltage, and current density are q...

A study of deformation-produced deep levels inn-GaAs using deep level transient capacitance spectroscopy

Deformation-produced deep levels, both of electron and hole traps, have been studied using deep level transient capacitance spectroscopy (DLTS) for an undopedn-type GaAs (HB grown) compressed at 440°C. Concentrations of two grown-in electron trap levels (Ec−0.65eV andEc−0.74eV) and one grown-in hole trap level (Ev+∼0.4eV) increase with plastic deformation, while that of a grown-in electron trap level (Ec−∼0.3eV) decreases in an early stage of deformation. While no new peak appeared in the electron trap DLTS spectrum after plastic deformation, in the hole trap DLTS spectrum a broad spectrum, seemingly composed of many peaks, newly appeared in a middle temperature range, which may be attributed to electronic energy levels of dislocations with various characters.

Current‐voltage characteristics and interface state density of GaAs Schottky barrier

A density distribution of the interface states in GaAs Schottky barrier was derived for the first time from observed nonideal I‐V characteristics of a GaAs Schottky barrier with an oxidized interface. With increasing forward bias voltage, the ideality factor increases and then decreases after passing a maximum. Fermi level of the interface states shifts with the applied bias in the interfacial layer model adopted for the analysis. The obtained energy level of the interface states is in agreement with a previously reported value. However, the absolute magnitude of the state density is quite small compared with that obtained from the weak dependence of the barrier height on metal work functions. Implications of this result are discussed.

Atomic microstructure and electronic properties of a‐SiNx:H deposited by radio frequency glow discharge

a‐SiNx:H films of various composition x were deposited by rf glow discharge (GD). The deposition rate was analyzed for three ranges of gas flow ratio R = [NH3]/[SiH4] depending on the deposition mechanism. Properties of these films were measured by means of x‐ray photoelectron spectroscopy (XPS), infrared (IR) absorption, optical absorption, and the temperature dependence of electrical conductivity. The composition x was determined by XPS. For large values of R, x was found to be saturated at 1.7. The variation of H content was detected by IR absorption. The variation of coordinating atoms of Si with increasing x was deduced from the variation of XPS spectra of the Si 2p core‐level and the shift of Si‐H stretching vibration frequency in IR absorption. Based on the random bonding model and assuming bonding units to the central Si atom to be Si, N, and NH, probabilities of Si tetrahedra with various coordinating units were obtained. The results indicate that there are many Si—Si bonds for the stoichiometric...

Recombination enhanced dislocation glide in InP single crystals

The glide mobility of dislocations in bulk n‐type InP single crystals was measured by the double‐etching method as a function of temperatures with or without 30‐keV electron beam irradiation. The mobility of β dislocations was found to be enhanced by the irradiation in such a manner that the mobility increase is caused by a decrease in the apparent activation energy, which is characteristic of recombination enhanced defect reaction phenomena. The enhancement is not much different in its magnitude from the same type of dislocations in GaAs.

Optical Bond Gap and Tauc Gap in a-SiOx:H and a-SiNx:H Films.

Changes in the joint density of state (JDOS) of a-SiOx:H and a-SiNx:H films with x were investigated by optical measurements. The optical bond gap E 0 which corresponds to the bonding-antibonding splitting energy was deduced from the dispersion of the refractive indices based on a single-oscillator model. The energy of the Si-Si bond, E 0 Si-Si, was estimated from E 0. The Tauc gap energy E t and the energy width of the linear tail were determined from optical transmission spectra. The correlation among these characteristic energies was investigated to estimate the JDOS in these alloys. It was found that E 0 Si-Si increases with x, while the bandwidth of JDOS derived from the Si-Si bond is kept constant for both a-SiOx:H and a-SiNx:H systems. This suggests that the increase in the Tauc gap energy is due to the increase in Si-Si bond energy rather than the change in the energy width of the Si-Si-bond-derived JDOS.

Dislocation-mobility-controlled cracking in gaas caused by constantrate indentation

Abstract The presence of a brittle to ductile transition (BDT) controlled by dislocation mobility previously found in Si has been observed for n-GaAs in the present study employing a novel type of dynamic fracture test (constant-rate indentation cracking test). This is a modification of the indentation-induced fracturing method for measuring the transition temperature, which is the critical temperature above which cracking ceases to occur as a function of loading rate. The BDT temperature thus measured was found to depend on the loading rate according to an Arrhhenius-type kinetic equation. Activation energies characterizing the equation varied with the geometrical type of crack formed by indentations on polar {111} planes of GaAs. The magnitudes of the activation energies for the BDT were found to be very close to those for motion of the dislocations that emanate from the respective types of crack tips. This result probably indicates that the BDT is caused by dislocation emission from crack tips, i.e. by...

Analysis of Si Schottky Barrier Characteristics Based on a New Interfacial Layer Model

Current-voltage characteristics of Si Schottky barrier diodes are measured at various temperatures between 300 K and 420 K in order to investigate an applicability of a newly proposed interfacial layer model for Schottky barrier. Experimental data are analyzed on a basis of this model. Analyzed results are mostly found to be similar to those of a-Si:H and can be interpreted by the present model. The new interfacial layer model is then concluded to well represent actual Schottky barriers for both amorphous and crystalline semiconductors.