MOS solar cells with oxides deposited by sol-gel spin-coating techniques

The metal-oxide-semiconductor (MOS) solar cells with sol-gel derived silicon dioxides (SiO₂) deposited by spin coating are proposed in this study. The sol-gel derived SiO₂ layer is prepared at low temperature of 450°C. Such processes are simple and low-cost. These techniques are, therefore, useful for largescale and large-amount manufacturing in MOS solar cells. It is observed that the short-circuit current (I _sc) of 2.48 mA, the open-circuit voltage (V _os) of 0.44 V, the fill factor (FF) of 0.46 and the conversion efficiency (η%) of 2.01% were obtained by means of the current-voltage (I–V) measurements under AM 1.5 (100 mW/cm²) irradiance at 25°C in the MOS solar cell with sol-gel derived SiO₂.     

Characterization of MIS structures and thin film transistors using RF-sputtered HfO2/HIZO layers

MIS structures using HfO₂ and HIZO layers, both deposited by room temperature RF magnetron sputtering are fabricated for TFTs application and characterized using capacitance-voltage. The relative dielectric constant obtained at 1 kHz was 11, the charge carrier concentration of the HIZO was in the range of (2–3) × 10¹⁸ cm^− 3 and the interface trap density at flat band was smaller than 2 × 10¹² cm^− 2. The critical electric field of the HfO₂ layer was higher than 5 × 10⁵ V/cm, with a current density in the operating voltage range below 4 × 10^− 8 A/cm². The hysteresis and bias stress behavior of RF-sputtered HfO₂/HIZO MIS structures is presented. Fabricated HfO₂/HIZO TFTs worked in the operation voltage range below 8 V.     

SONOS-type flash memory using an HfO/sub 2/ as a charge trapping layer deposited by the sol-gel spin-coating method

In this letter, the authors fabricate the silicon-oxide-nitride-oxide-silicon (SONOS)-like memory using an HfO/sub 2/ as charge trapping layer deposited by a very simple sol-gel spin-coating method and 900 /spl deg/C 1-min rapid thermal annealing. They examine the quality of sol-gel HfO/sub 2/ charge trapping layer by X-ray photoemission spectroscopy, Id-Vg, charge retention, and endurance. The threshold voltage shift is 1.2 V for the sol-gel HfO/sub 2/ trapping layer. The sol-gel HfO/sub 2/ film can form a deep trap layer to trap electrons for the SONOS-like memory. Therefore, the sol-gel device exhibits the long charge retention time and good endurance performance. The charge retention time is 10/sup 4/ s with only 6% charge loss and long endurance program/erase cycles up to 10/sup 5/.     

High frequency capacitance-voltage and conductance-voltage characteristics of d.c. sputter deposited a-carbon/silicon MIS structures

Dark and illuminated C–V and G–V characteristics of A1/a-carbon/silicon MIS structures have been measured in the frequency range of 10 kHz to 10 MHz. The a-carbon passivating layer is prepared by d.c. sputtering of a graphite target in Ar gas. There is no evidence of Fermi level pinning, and surface carrier inversion is clearly demonstrated. Electrical instabilities are noted and briefly discussed. The high frequency electrical behavior seems to be dominated by states in the dielectric rather than states at the interface. a-carbon appears to be a promising dielectric material for use in silicon solid state electronics.     

Electrical characterization of AlN MIS and MIM structures

Aluminum nitride (AlN) thin films have been deposited on p-Si[100] and Mo-Si[100] substrates. The sputter deposited Mo was polycrystalline, predominantly showing a [110] orientation. Thin AlN films were grown under different process conditions in a physical vapor deposition (PVD) system to attain highly textured polycrystalline films as well as close to amorphous films. MIS and MIM structures were fabricated and electrical properties such as the dielectric constant, leakage current, and high-frequency behavior were investigated. It is found that the dielectric constant is 10 and does not change with the crystallinity of the films. High-frequency measurements up to 10 GHz show no frequency dispersion of the capacitance. The leakage current stays relatively constant between films and is believed to be Poole-Frenkel controlled. Capacitance-voltage (C-V) measurements for MIS structures revealed the presence of charges in the interface layer between the substrate and the dielectric film. The temperature dependence of the capacitance has also been studied.     

GaAs MIS structures with SiO2 using a thin siliconinterlayer

The introduction of a pseudomorphic Si interlayer, about 1.0 nm thick, is found to dramatically improve the MIS characteristics of the SiO₂-GaAs system. Quasistatic and high-frequency capacitance/voltage data from such a novel capacitor structure on n -GaAs indicate that the surface of the GaAs is swept from inversion to accumulation. X-ray photoelectron spectroscopy and ion scattering spectroscopy confirm the presence of the Si layer and its complete coverage of the GaAs surface. The Si layer minimises the formation of any detrimental native oxides and thus controls the chemical nature of the GaAs surface. This approach has implications in the development of metal-insulator-semiconductor systems in general     

Electrical properties of inhomogeneous SiC MIS structures

Current-voltage characteristics of metal contacts on 6H-SiC with a thin (5–20Å) oxide layer have been measured in the temperature range 300 to 1000K. The contacts were investigated in both H₂ and O₂-atmospheres. As the SiC surface was nonideal due to pin holes and other defects generated during the growth process, it was necessary to treat the Schottky contacts as inhomogeneous contacts. The inhomogeneity explains the nonideal current-voltage behavior of the contacts such as ideality factors much larger than unity and voltage dependent ideality factors. It was found that some metals gave Schottky contacts in the entire temperature range, while other metals were ohmic at higher temperatures. Several different contact metals were investigated: Al, Ti, TaSi_x, and Pd were found to be ohmic at high temperatures, while Pt, Pt+Cr, Ni, Cr and another TaSi_x contact were found to behave like Schottky contacts in the entire temperature range. This is a preliminary investigation of the electrical characteristics of different metals that could be useful for high temperature gas sensor purposes.     

Practical aspects of producing MIS structures with good prospects using atomic layer deposition technology

The physical and chemical foundations of the atomic layer deposition (ALD) process, the advantages of ALD technology, and possible applications for further miniaturizing and improving the performance of semiconductor devices are considered. The results of the atomic layer deposition of the advanced nanoelectronic material hafnium oxide are discussed. The dielectric characteristics’ measurements and microstructure analysis results are given.     

Deposition of thin refractory MIS structures on InP

In the present investigation, we report on significant increases in the refractory-InP Schottky barrier by process modification of the metal-semiconductor interface. Refractory-InP MIS structures were investigated as pos-sible gate metallizations. These structures consisted of Ta/Ta₂}O₅}/InP and TiW/TiO₂} /InP. A thin layer of Ta (100å) was electron beam vapor aeposited followed by the in situ formation of Ta₂}O₅} at 300?C and an oxygen overpressure. The remainder of the Ta film was deposited at 90?C substrate temperature. The TiW/TiO₂} system was formed by sputter deposition of Ti (100A?), in situ oxidation to form TiO₂} followed by deposition of TiW (88 wt % W, 12 wt % Ti). Effective barrier height for the TiW/TiO /InP structure was measured to be 0.65 eV and for the Ta/Ta₂}O₂} /InP, 0.5 eV. Leakage current at-5V was less than 3 A/cm²} for both refractory-InP MIS structures. The TiW/TiO₂} /InP structure was stable up to 400-450°C, while the Ta/Ta₂ O₅/InP system degraded to 0.2 eV at 300-350?C.     

Stable gallium arsenide MIS capacitors and MIS field effecttransistors by (NH4)2Sx treatment andhydrogenation using plasma deposited silicon nitride gate insulator

The beneficial effects of sulfur passivation of gallium arsenide (GaAs) surface by (NH₄)₂S_x chemical treatment and by hydrogenation of the insulator-GaAs interface using the plasma-enhanced chemical vapor-deposited (PECVD) silicon nitride gate dielectric film as the source of hydrogen are illustrated by fabricating Al/PECVD silicon nitride/n-GaAs MIS capacitors and metal insulator semiconductor field effect transistors (MISFET). Post metallization annealing (PMA) at temperatures in the range 450-550°C is shown to be the key process for achieving midgap interface state density below 10 ¹¹/cm²/eV and maximum incremental transconductance, which is about 75% of the theoretical maximum limit. MIS capacitors are fabricated on (NH₄)₂S_x treated GaAs substrate using gate dielectrics such as PECVD SiO ₂ and silicon oxynitride to demonstrate that the PMA is less effective with these dielectrics because of their lower hydrogen content. The small signal AC transconductance, g_ms measurements on MISFETs fabricated using silicon nitride, have shown that the low-frequency degradation of g_ms is almost absent in the devices fabricated on (NH₄)₂S_x-treated GaAs substrates and subjected to PMA. The drain current stability in these devices is demonstrated to be excellent, with an initial drift of only 2% of the starting value. The dual role of silicon nitride layer, namely, protection against loss of sulfur and an excellent source of hydrogen for additional surface passivation along with sulfur is demonstrated by comparing the transconductance of MISFETs fabricated on GaAs substrates annealed without the nitride cap after the (NH₄)₂S _x treatment     

Properties of MIS structures based on graded-gap HgCdTe grown by molecular beam epitaxy

The effect of near-surface graded-gap layers on the electrical characteristics of MIS structures fabricated based on heteroepitaxial Hg_{1 ? x} Cd _x Te films grown by molecular beam epitaxy with a two-layer SiO₂/Si₃N₄ insulator and anodic oxide film is studied experimentally. It is shown that a larger modulation of capacitance (depth and width of the valley) is observed compared with the structures without the graded-gap layer. The field dependences of photovoltage of MIS structures with the graded-gap layers had a classical form and were characterized by a drop only in the enrichment region. For the structures without the graded-gap layer with x = 0.22, a drop in the voltage dependence of the photocurrent is observed in the region of pronounced inversion. This drop is governed by limitation of the space charge region by processes of tunneling generation via deep levels. The properties of the HgCdTe-insulator interfaces are studied.     

利用ICPCVD方法在GaN上沉积氧化硅薄膜的特性

使用感应耦合等离子体化学气相沉积(Inductively coupled plasma chemical vapor deposition,ICPCVD)方法在GaN上沉积SiOx薄膜,生长参数中采用不同RF功率,研究RF功率对薄膜物理性能和电学性能的影响.结果发现,随着RF功率增大,薄膜应力增大,表面粗糙度减小,薄膜致密度增大.选择最优的RF功率参数,制作了SiOx/nGaN金属-绝缘体-半导体(metal-insulator-semiconductor,MIS)器件,结果得到薄膜漏电流密度在外加偏压为90V时小于1×10-7A/cm2,SiOx/n-GaN界面态密度为2.4×1010eV-1cm-2.表明利用ICPCVD低温沉积的SiOx-GaN界面态密度低,薄膜绝缘性能良好.     

Electronic properties of InAs-based metal-insulator-semiconductor (MIS) structures

Special features of electronic processes in InAs-based MIS structures operating in the charge injection mode were investigated. These structures are used as photodetectors in the spectral range of 2.5–3.05 μm. A double-layer system consisting of an anodic oxide layer and a low-temperature silicon dioxide layer was used as an insulator. It was shown that fluorine-containing components, which were introduced into electrolyte, reduced the value of the built-in charge and the surface-state density to minimal measurable values of ≲2×10¹⁰ cm⁻² eV⁻¹. Physical and chemical characteristics of the surface states at the InAs-insulator interface and the possible causes of their absence were discussed on the basis of the phase composition data of anodic oxide obtained by X-ray photoelectron spectroscopy. An anomalous field generation was observed under the nonequilibrium depletion of the semiconductor. The processes of tunneling generation, which are important at large amplitudes of the depletion pulse, were considered. The noise behavior of MIS structures under a nonequilibrium depletion was investigated. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 35, No. 9, 2001, pp. 1111–1119. Original Russian Text Copyright ? 2001 by Kuryshev, Kovchavtsev, Valisheva.     

MIS slow-wave structures over a wide range of parameters

Lossy multilayer, multiconductor MIS microstrip structures are analyzed with the spectral-domain approach over a wide range of frequency and substrate loss. The modal attenuation and propagation constants are presented for two- and four-conductor structures as a function of the substrate loss tangent. Single-conductor structures are characterized with contour plots showing the complex effective dielectric constant as a function of both frequency and conductivity. MIS slow-wave structures are analyzed for both Si-SiO₂ and GaAs configurations     

Fabrication of ZnO colloidal photonic crystal by spin-coating method

We describe a simple and effective method, based on spin coating, developed for the fabrication by self-assembly of ZnO colloidal photonic crystal structures. The scanning electron microscope images indicate ordered structures with few defects. All the ordered structures exhibit a stop band in optical transmission experiments. The position of the stop band scales nicely with the particles size, indicating that it is an intrinsic feature of the photonic crystals. With decrease of ZnO particles size, the positions of the band are shifted to the shorter wavelength.     

Initial and radiation-induced charge distribution in silicon oxynitride MIS structures

Silicon oxynitride films deposited on a HF-etched Si surface show a large fixed positive charge in the dielectric (2-3 × 10^-2cm^-2). This charge is shown by etch-back experiments to be located near the silicon-oxynitride interface. Negative charge is injected into the oxynitride film if a negative bias larger than 2.8 × 10⁵V/cm is applied during irradiation. For saturation doses (about 1-2 Mrad of absorbed radiation), the magnitude of the injected charge can become as large or larger than the original positive charge in the oxynitride. The injected negative charge, is shown to be located at the silicon-oxynitride interface by etch-back experiments. The injection of negative charge under the above conditions appears to be an electronic phenomenon. An ionic mechanism appears unlikely because re-irradiation at room temperature without application of a bias restores the original flat-band condition of the MIS capacitor.     

Characterization of CdSe thin films deposited by chemical bath solutions containing triethanolamine

Cadmium selenide (CdSe) thin films were prepared by chemical bath deposition on glass substrates at different temperatures beginning at room temperature (25 °C) upto 80 °C from an aqueous alkaline medium using a precursor solution containing cadmium acetate, 2,2′,2′′-nitrilotriethanol (triethanolamine), ammonia and sodium selenosulphate. The pH of bath was kept constant around 10.50±0.10. Energy dispersive analysis of X-rays confirmed that the films are nearly stoichiometric in composition. The structural and surface morphological properties have been studied by X-ray diffraction, Scanning electron microscopy and Atomic force microscope techniques. X-ray diffraction study reveals a cubic structure with preferential orientation along (111) direction. The dependency of structural parameters such as crystallite size, strain and dislocation density with different bath temperatures for CdSe thin films are calculated. X-ray peak broadening was used to evaluate the crystallite size and lattice strain by the Williamson–Hall plots. Optical properties are studied by photoluminescence spectra which shows blue shift in peak position and reduction in luminescence intensity were observed for films deposited at different bath temperatures.     

Slow relaxation of conductance of quasi-two-dimensional highly disordered MIS structures

Slow relaxation of 2D conductance of metal-nitride-oxide-semiconductor structures is investigated with various methods of disturbing the system from equilibrium. It is shown that slow relaxation appears only under a strong fluctuation potential, which is controllable in these systems. The main process determining conduction of the system is screening of the potential by channel electrons, both by free electrons and those localized in potential wells. The time dependence of conductance is logarithmic, which is typical of systems of the “electronic glass” type.