Ge/GaAs(100) Thin Films: Large Effect of Film Growth Rate and Thicknesses on Surface Morphology, Intrinsic Stresses and Electrical Properties

We found out and studied a profound effect of film growth rate on the electrical properties, intrinsic stresses and surface morphology of thin Ge films grown on GaAs(100). This effect is essential and has to be accounted for when developing and producing devices based on the Ge/GaAs heterostructure. All the Ge films under investigation were single-crystalline and epitaxially-grown on the GaAs(100) substrates. However, the transport phenomena in Ge films grown at low and high deposition rate differed drastically. Those obtained at low deposition rate were p-type and high resistant. They had a low concentration of free charge carriers and thermally activated conductivity, which is characteristic of heavily doped and strongly (in the limiting case, fully) compensated semiconductors. Although such films were single-crystalline, their conductivity was percolation-type. The Ge films obtained at high deposition rate were n-type and low resistant. They had high concentration of free charge carriers. The temperature dependence of conductivity in such films was weak or practically absent, which is characteristic of degenerate heavily doped semiconductors. Besides, the surface morphology cardinally differed for films obtained at low and high deposition rate. At low film growth rates, surfaces with developed relief were observed whose valleys and ridges formed grains of irregular shape with pronounced substructure. As the film thickness grew, the surface relief became essentially pronounced. At rather high film deposition rates, contrary to the above, the Ge film surface was fine-grained and smooth; the surface relief practically did not depend on the film thickness. As the deposition rate went down, the intrinsic stresses in films essentially decreased. The results obtained were analyzed from the viewpoint of formation of compositional and morphological inhomogeneities, and fluctuations of electrostatic potential at low growth rates. Such potential fluctuations modulate Ge energy bands leading to appearance of potential relief and deep tails of density of states in the Ge bandgap. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3506

A silicon carbide thermistor

We consider a silicon carbide thermistor with multilayer Au–TiBx–Ni2Si ohmic contacts intended for operation in the 77 to 450 K temperature range

Switching waves in asymmetric thyristor-like structures for incomplete gate turn off regime

A stationary wave of switching is considered in an infinite thyristor-like structure (TLS).This wave is initiated by the controlling gate current which differs from a certain equilibrium current Jg0(j) providing a neutrally equilibrium (translationally invariant) position of the transition layer between a blocked (OFF-) region and an open (ON-) region for a given current density j in the ON-region. The dependence of the wave velocity v(Jg, j) on the gate current Jg and the current density j is derived.We deal with structures in which the conductivity of gated base I is much higher than the conductivity of ungated base II.The injection level is considered low for base I and high for base II. It is shown that the velocity of the switching wave (i.e. the speed of transient processes in TLS) is determined mainly by parameters of base II. It is also demonstrated that a high speed of operation can be reached in structures with a moderately long base II (the length of the base should exceed 1-2 bipolar diffusion lengths) and a small lifetime of carriers in this base.This work was supported by the National Science Foundation of the USA. One of us (Z. S. Gribnikov) thanks the Ukrainian Foundation of Fundamental Researches for a partial support. We also thankful to the editorial board of the «Semiconductor Physics, Quantum Electronics & Optoelectronics» for the invitation to submit our paper to the first issue of this new journal. Розглянуто стаціонарну хвилю переключення в кінцевій тиристоро подібній структрурі (ТПС). Ця хвиля ініційована контролюючим струмом затвору I g, який відрізняється від певного рівноважного струму I g0(j), який забезпечує положення нейтральної рівноваги (трансляційно інваріантної) перехідного шару між запертою та відкритою областями для даної густини струму j у відкритій області. Виведено залежність швидкості хвилі v(I g, j) від струм

Study of Structure and Intrinsic Stresses of Ge Thin Films on GaAs

The effect of film growth rate on the structure and intrinsic stresses of thin (100 nm) Ge films grown on GaAs(100) substrates was investigate by High Resolution X-Ray Diffraction (HRXRD). The Ge films were deposited onto GaAs using thermal evaporation of Ge in the vacuum. It was shown that pseudomor-phic films with good structural quality can be obtained by this growth technique. We found out that the films have biaxial deformations due to coherent interface and Poisson ratio. The films are elastically com-pressed in the interface and stretched in the perpendicular [001] direction. The intrinsic deformations of thin Ge films strongly depended on the deposition rate. Their correlations with surface roughness, electri-cal and optical parameters are discussed. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3531

Ohmic contacts to Hall sensors based on n-InSb-GaAs(i) heterostructures

We consider ohmic contacts to the n-InSb epitaxial layers grown on a semi-insulating GaAs substrate. The ohmic contacts are formed through titanium metallization with subsequent gilding. Using the structural (AFM and XRD) and analytical (AES) techniques, we showed that thermal annealings at Т = 300 °С (for 60 s) and 360 °С (for 30 s) do not change the phase composition of the metallization. This ensures thermal stability of the contacts and Hall sensors made on the basis of Au–Ti–n-InSb–GaAs(i) structures

Suppression of non-Poissonian shot noise by Coulomb correlations in ballistic conductors

We investigate the current injection into a ballistic conductor under the space-charge limited regime, when the distribution function of injected carriers is an arbitrary function of energy F_c(epsilon). The analysis of the coupled kinetic and Poisson equations shows that the injected current fluctuations may be essentially suppressed by Coulomb correlations, and the suppression level is determined by the shape of F_c(epsilon). This is in contrast to the time-averaged quantities: the mean current and the spatial profiles are shown to be insensitive to F_c(epsilon) in the leading-order terms at high biases. The asymptotic high-bias behavior for the energy resolved shot-noise suppression has been found for an arbitrary (non-Poissonian) injection, which may suggest a new field of investigation on the optimization of the injected energy profile to achieve the desired noise-suppression level.Comment: extended version 4 -> 8 pages, examples and figure adde

Suppression of non-Poissonian shot noise by Coulomb correlations in ballistic conductors

We investigate the current injection into a ballistic conductor under the space-charge limited regime, when the distribution function of injected carriers is an arbitrary function of energy F_c(epsilon). The analysis of the coupled kinetic and Poisson equations shows that the injected current fluctuations may be essentially suppressed by Coulomb correlations, and the suppression level is determined by the shape of F_c(epsilon). This is in contrast to the time-averaged quantities: the mean current and the spatial profiles are shown to be insensitive to F_c(epsilon) in the leading-order terms at high biases. The asymptotic high-bias behavior for the energy resolved shot-noise suppression has been found for an arbitrary (non-Poissonian) injection, which may suggest a new field of investigation on the optimization of the injected energy profile to achieve the desired noise-suppression level.Comment: extended version 4 -> 8 pages, examples and figure adde

Plasma metallization coating and its adhesion to microwave transistor substrate - Part 2: Experimental study of 3-D composite coating

This paper reports an experimental study of the previously proposed mechanism of adhesion of a plasma metal coating to a ceramic substrate by an example of beryllium oxide. This adhesion mechanism is based on the increase in the concentration of structural defects (vacancies) and electron exchange interaction of a metal-oxide beryllium pair during the plasma thermal activation of the process. Given the brazing of ceramic products with hard solders in hydrogen, the coating composition for metallization is determined. The optimal temperature of reactive plasma metal coating for strong adhesion to the ceramic substrate is found. Methods to improve the technology of plasma vacuum metallization using ion-plasma magnetron sputtering and ion implantation are proposed. Recommendations for the deposition of 3-D composite coatings with maximum adhesion are given. © 2015 IEEE

Plasma metallization coating and its adhesion to microwave transistor substrate - Part 1: Methods of experimental research

A previously proposed mechanism of adhesion of a plasma metal coating to a ceramic substrate is investigated experimentally. This adhesion mechanism is based on the increase in the concentration of structural defects (vacancies) and electron exchange interaction of a metal-oxide beryllium pair during the plasma thermal activation of the process. Given the brazing of ceramic products with hard solders in hydrogen, the coating composition for metallization is determined. The optimal temperature of reactive plasma metals coating for strong adhesion to the ceramic substrate is found. Methods to improve the technology of plasma vacuum metallization using ion-plasma magnetron sputtering and ion implantation are proposed. © 1973-2012 IEEE

Plasma metallization coating and its adhesion to microwave transistor substrate - Part 2: Experimental study of 3-D composite coating

This paper reports an experimental study of the previously proposed mechanism of adhesion of a plasma metal coating to a ceramic substrate by an example of beryllium oxide. This adhesion mechanism is based on the increase in the concentration of structural defects (vacancies) and electron exchange interaction of a metal-oxide beryllium pair during the plasma thermal activation of the process. Given the brazing of ceramic products with hard solders in hydrogen, the coating composition for metallization is determined. The optimal temperature of reactive plasma metal coating for strong adhesion to the ceramic substrate is found. Methods to improve the technology of plasma vacuum metallization using ion-plasma magnetron sputtering and ion implantation are proposed. Recommendations for the deposition of 3-D composite coatings with maximum adhesion are given. © 2015 IEEE