Conditions preventing thermal breakdown in semiconductor devices

We present results facilitating the prediction of the possibility of thermal breakdown in semiconductor devices and selection of the working parameters preventing such breakdowns.     

Microstructure formation in chalcogenide thin films assisted by thermal dewetting

The spontaneous formation of self-assembled and/or self-organized patterns is a fundamental and technologically significant topic. This process is achieved via a phenomenon called dewetting, should it be thermally induced, or caused by laser exposure. Although dewetting seems to be a well-known phenomenon for metallic and polymeric thin films, no proper investigation regarding glassy thin films seems to have been done. Thus, in the present study we try to elaborate on the process of thermal dewetting applied to glassy thin films of the system Ag_x(As₂₀S₈₀)_100?x.     

Preferential growth of thin rutile TiO2 films upon thermal oxidation of sputtered Ti films

Thin rutile TiO₂ films with (200) preferred orientation were fabricated by thermal oxidation of sputtered Ti metal films on a fused silica substrate. Experimental results indicate that the preferential crystal growth of (200)-oriented TiO₂ is determined by the competition between surface free energy and strain energy. The highly crystalline Ti film with (002) orientation has a greater tendency to promote the growth of (200)-oriented TiO₂. However, for the amorphous and low crystalline Ti films, orientation of the crystallites evolved in the resulting TiO₂ film tends to be randomly distributed. The extent of preferential crystal growth of TiO₂ (200) plane can be enhanced by decreasing the annealing temperature or the thickness of Ti film.     

Thickness dependence of breakdown field in thin films

Studies of the thickness dependence of dielectric breakdown in thin films are of fundamental importance for the development of devices. Here a systematic study of the d.c. breakdown in “built-up” ionic films of barium stearate is reported in the thickness range (25–2000 Å). These films are ideally suited for such studies because of their perfect reproducibility and control of their thicknesses which are uniform and very accurately known. The breakdown strength is found to be a power dependent function of thickness as predicted by Forlani and Minnaja's theory based on an electron ionization avalanche mechanism. The films studied have recently been found to be promising for making devices.     

Complicated quasi-particle complexes in thin semiconductor films

The formation of complicated quasi-particle complexes (mainly the biexciton ions, the exciton molecules and exciton-donor neutral complexes) in thin semiconductor films has been investigated theoretically. Analytical expressions have been obtained for the dissociation energies of these quasi-particle complexes as functions of the ratio of the effective mass of the electron to that of the hole. The conditions for the formation of such complexes are shown to be more favourable in thin films than in bulk semiconductors.

The influence of a homogeneous magnetic field on the dissociation energy of biexciton ions in a bulk semiconductor is also investigated.     

Lasing action in organic semiconductor thin films

Lasing action in optically pumped thin films of organic semiconductors has recently been demonstrated in a variety of materials employing a variety of cavity configurations. The excitation intensities required for lasing in optically pumped films are comparable to the electrical current densities achievable in light emitting devices based on these materials, opening the door to the possible realization of organic diode lasers. However, the design of diode laser structures is complicated by the relatively low charge carrier mobilities of organics. It has also been shown that the optical properties of organic films under electrical excitation are affected by the formation of polarons, imposing yet another obstacle for realization of these devices. The continuing research on organic diode lasers is motivated by the unique properties of these devices, such as narrow spectral emission linewidth and the temperature independence of laser output power and emission wavelength, which may be advantageous in a number of applications.     

Electrical breakdown studies in didymium oxide thin films

I–V characteristics of sandwiched Al-didymium oxide-Al structures are studied for different thicknesses. The breakdown voltage increases and the dielectric strength decreases with increase of film thickness. Optical photomicrographs of the breakdown patterns during different stages of dc voltage are taken and the results discussed.     

Processing of nanocrystalline diamond thin films for thermal management of wide-bandgap semiconductor power electronics

High current densities in wide-bandgap semiconductor electronics operating at high power levels results in significant self-heating of devices, which necessitates the development thermal management technologies to effectively dissipate the generated heat. This paper lays the foundation for the development of such technology by ascertaining process conditions for depositing nanocrystalline diamond (NCD) on AlGaN/GaN High Electron Mobility Transistors (HEMTs) with no visible damage to device metallization. NCD deposition is carried out on Si and GaN HEMTs with Au/Ni metallization. Raman spectroscopy, optical and scanning electron microscopy are used to evaluate the quality of the deposited NCD films. Si device metallization is used as a test bed for developing process conditions for NCD deposition on AlGaN/GaN HEMTs. Results indicate that no visible damage occurs to the device metallization for deposition conditions below 290 °C for Si devices and below 320 °C for the AlGaN/GaN HEMTs. Possible mechanisms for metallization damage above the deposition temperature are enumerated. Electrical testing of the AlGaN/GaN HEMTs indicates that it is indeed possible to deposit NCD on GaN-based devices with no significant degradation in device performance.     

Electrical conduction mechanisms in thin amorphous semiconductor films

An account is given of the different conduction mechanisms possible in thin amorphous semiconductor films. Special attention is paid to the low temperature regime where variable range hopping between states near the Fermi level is supposed to be most important. An attempt is made to assess the significance of fits of the conductivity versus temperature relation to the much-used T^{-$\text{1}\text{4}$} relation proposed by Mott.     

Microstructural evolution of oxides and semiconductor thin films

This review article introduces the preparation methodologies and the microstructural characteristics of semiconductor thin films, including SnO₂ thin films, Au/Ge bilayer films, and Pd-Ge alloy thin films, and metal oxides, including SnO, SnO₂, Mn₂O₃ and Mn₃O₄ nanocrystals which can be in the form of nanoparticles, nanowires, nanorods, and nanofractals. Firstly, the preparation methodologies and the microstructural characteristics of tin oxides have been investigated in detail and described in Section 2. Secondly, the crystallization of amorphous Ge, and the formation of nanocrystals and compounds developed with improved micro- and nanostructured features are described in Section 3. Thirdly, a novel selective synthesis route for various morphologies of manganese oxides nanocrystals, including nanoparticles, nanorods and nanofractals, and their unique microstructural characteristics are presented in Section 4. Intricate fundamental properties of manganese oxides nanocrystals are studied in detail. To sum up, it is expected that the fabrication methodologies developed and the knowledge of microstructural evolution gained in semiconductor thin films, including SnO₂ thin films, Au/Ge bilayer films, and Pd-Ge alloy thin films, and metal oxides, including SnO, SnO₂, Mn₂O₃ and Mn₃O₄ nanocrystals in the forms of nanoparticles, nanowires, nanorods, and nanofractals, will provide an important fundamental basis underpinning further interdisciplinary (physics, chemistry and materials science) research in this field leading to promising exciting opportunities for future technological applications involving these oxide and thin film materials.     

Electrodeposition and characterization of CdSe semiconductor thin films

The electrodeposition of cadmium selenide alloy on glassy carbon and gold electrodes has been studied by electrochemical techniques. Potentiostatic I-t transients were recorded to obtain the nucleation mechanism, while cyclic voltammetry was used to characterize the system. Structural information on the electrodeposited layers was obtained by X-ray diffraction. The experimental results clearly show that the deposition of cadmium selenide alloy on glassy carbon and gold electrodes is a diffusion-controlled process. The nucleation is progressive, and the number of nucleation sites decreases with increasing bath temperature. The deposition of CdSe alloy results in well-defined crystals with hexagonal shape. The films were characterized by optical absorption and electrical resistivity measurements. Films showed a direct band gap of 3.56 eV.     

氢敏元件的种类及半导体薄膜材料在其中的应用

随着氢燃料电池技术在汽车应用中的日益完善,对高性能氢敏元件的需求也更加迫切。本文介绍了采用不同工作原理制备的氢敏元件的种类,着重描述了半导体薄膜材料的工作原理和改性途径,并针对我国目前研究较少的Ga2O3新型薄膜材料进行了较为详细的综合论述。     

Picosecond thermal pulses in thin gold films

In this paper it has been shown that, with the advent of lasers with a very short pulse duration, the effect of thermal wave propagation becomes important. To consider this effect, hyperbolic heat conduction in thin gold films was studied. It was shown that for heat fluxes of the order 10⁸ W·cm^–2, a thermal wave is generated in thin gold films. The consideration of the hyperbolicity of heat transfer enables one to describe the temperature profile with one value of fluence.