Influence of the ultrasonic irradiation on characteristic of the structures metal-glass-semiconductor

The studied influence ultrasonic irradiation on change the rolling charge built-in in structure lead borosilicate glasses PbO - SiO2 - B2O3 - Al2O3 - Ta2O5. It is shown that influenc ultrasonic irradiation brings about reduction of the rolling charge and improvement insulation parameter glass.


Introduction
The study of external influences on semiconductor structures is relevant, a lot of work done in this area is evidence of this .The structures of the type metal -insulator-semiconductor (MIS) on base silicon at present are a base of the broad class semiconductor instrument and structured element of the integral schemes. Herewith, features of the border of the section, semiconductor -insulator, being the most sensitive to external influence, can render the essential influence upon parameters made instrument and structured element [1,2]. The studies of the influence, on parameters of the borders of the section, such influence as termal processing and ionizing irradiation is denoted it is enough much works [3,4]. As to influences ultrasonic influence, that available given not it is enough are broadly interpreted. So, in work [6,19] is shown that ultrasonic influence can bring both to reduction, and to increase the charge, localized on interphase border section SiO 2 -p-Si. In work [7,20] is shown, ultrasonic irradiation brings about realignment tense valence relationships on hiding border of the section semiconductor-glass, with simultaneous increase the section of the seizure localized electron on them. Lead-borosilicate glasses are free from these shortcomings. Moreover, use of fusible lead borosilicate glasses permit to combine high insulating characteristics and simplicity of dielectric coverings obtaining. From this point of view, research of the nature of electrophysical processes taking place in the lead -borosilicate glasses coverings under external influence conditions is actual.The purpose persisting work was study of the influence of the ultrasonic influence on value of the rolling charge, available in structure leadena borona silicate glass.

Materials and Methods
The test structures were fabricated by applying glass to a Si, n-type conductivity substrate, with a crystallographic orientation of <100>. The glass was applied by electrophoresis from a suspension containing a fine-dispersed glass batch (SiO 2 -PbO-B 2 O 3 -Al 2 O 3 -Ta 2 O 5 ) and isopropyl alcohol, followed by reflow at a temperature of 670-680 degrees in Celsius and annealing in an oxygen-free atmosphere. The thickness of the obtained glass layers was d = (2  0.2) 10 -4 cm. The mass content of the oxides included in the glass was: SiO 2 -30%; PbO-50%; B 2 O 3 -15%. The investigated glasses also contained aluminum and tantalum oxides with mass fractions of 5% and alkali metal oxides of Na 2 O and Na 2 O whose mass fractions did not exceed 0.01%. MIS structures were made by vacuum deposition of aluminum on the surface of the glass layer. The diameter of the control electrodes is 3 mm. The structures were subjected to irradiation with longitudinal ultrasonic waves at a frequency of 2.5 mHz with a power of 0.5 W, for 40 minutes, i.e. An effect similar to that described in [7,20] was used. The acoustic line between the piezoelectric transducer and the structure under study was a liquid. The method of isothermal relaxation of the capacitance of the metal-insulator-semiconductor (MIS) structure in the process of increasing the charge of the inversion layer was used as the main research method [8,9,21,22]. In accordance with the generally accepted model of the MIS structure, the time dependence of the capacitance of this structure, after the impulse increase of the applied voltage, (without taking into account the influence of the forming charge of the inversion layer) can be expressed by the following relation: Here: K -is the area of the control electrode, C D -is the capacitance of the dielectric layer, ε -is the dielectric constant of the semiconductor, ε 0 -is the electric constant, and x(t) -is the time dependence of the width of the space charge region (SCR) of the semiconductor. The value of C D -is determined by the high-frequency current-voltage characteristic. The quantity C(t) can be found, for each instant t, from the experimental relaxation characteristic of the MIS structure, using the expression (1) and (2): Here: x -is the thickness of the space-charge layer of semiconductor of the MIS structure; x 0 -is the initial thickness of this layer; A -is the rate of generation of charge carriers in the bulk of semiconductors; S -is the rate of surface generation of charge 0063arriers; N -is the concentration of the dopant. The resulting calculated time dependence of the width of the SCR can be used to determine the values of the velocity of surface and volume generation of charge carriers when compared with the experimental dependence.
To study the energy spectrum of bulk states localized in silicon, the identification technique described in [8] was used, for which Schottky type Au-n-Si diodes were fabricated by chemical removal of the glass layer and vacuum deposition of Au.

Results and Discussions
On drawing 1 is brought C-V feature (normalized to value of the capacities layer flow) of one of the under investigation structures, measured in the dark, on frequency 150 kHz before influence by ultrasound -a dependency 1 and after influence (the frequency 2,5 mHz power 0,5 Vt, in current 20 minutes) -a dependency 2. It is seen that after influence by ultrasound, C-V feature moves aside negative voltages and not vastly changes its form. The parallel shift C-V features of the structures MIS (made on base of the semiconductor n -a type to conductivities) aside negative voltages points to formation positive charge in structure glass. But change the form C-V features of such structures, is indicative of increase the charge of the surface conditions, which are recharged when change the value of the put voltage. Presence of the rolling charge in structure leaden -a boron -silicate flow is conditioned localization, injection from semiconductor, electron in approach easy polarization ions lead and agglomeration them on potential barrier of the enabling the crystalline phase [3]. In our opinion, the main reason, bring about increase the positive charge, can be a change the height potential barrier between enabling the crystalline phase. Really, reduction of the height potential barrier brings about that incorporated by attached voltage, from semiconductor electrons, not localizing in greater amount in potential pit, when change the polarities of the voltage, return back in volume of the semiconductor substrate. For confirm this hypothesis the ultrasound effects were measured at different temperatures (-10 0 С -+ 50 0 С) and frequencies (100 kHz -1MHz) in dielectrics. The comparison of the obtained thermalfrequency connections in all the measured constructions is allows to estabilish that the dielectric loss tangent have the characteristic maximum. In ultrasound structures, the relaxation maximum of the dielectric losses decreases and becomes more pronounced.Such a change in the relaxation maximum also shows an increase in the magnitude of the moving charges in the glass structure.  The probability of calculating the calculated connection from the experimental to the end of the relaxation process is that the inversion increases with the charge level and increases the likelihood of retrieval of generated chargers. For similar samples, however, under the influence of ultrasound, the capacitance relaxation is given in connection 3. From these links, it is clear that the calculated (2.4) and experimental (1.3) connections are well-suited to the values A = (8-9)·10 13 s -1 cm -3 , S=(1-2)·10 9 s 1 sm -2 . In our case, this situation indicates that energy intake of semiconductor concentration centers is practically unchanged as a result of processing at ultrasonic values and decreases the surface generation rate (S=4·10 9 s -1 sm -2 , S=(1-2)·10 s -1 sm -2 ultrasound samples). In order to confirm this assumption, the glass layers were removed from the ultrasound effectively by the chemical method (with formic acid vapor treatment) and the Au-n-Si type Shottky diode was prepared. Then the method of isothermal relapse of the capacitance [8] determined the concentration of localized centers of power distribution and diode base. Analysis of the results shows the following. In all the Shotki diodes, under the control of both ultrasound effects, the energy state of the centers (Е V -0,27эВ and E C -0,54эВ, as well as their concentration n = (3-5)·10 12 sm -3 ) is practically the same (for different diodes the value of the value is 5-7%) and is lies in the error of the experiment. In our opinion, this given ultrasound does not affect to parameters of centers of volumetric generation, in results as chargers do not affect the speed of the volume generation. Immediate measurements of the density of the surface state by the high-frequency volt-farad method have shown [9,10,19,20] (at a frequency of 150 kHz, from -50 0 S to -180 0 S) (Fig.4) that in structures subjected to ultrasound, the distribution of intrinsic density over the width of the semiconductor zone width decreases in comparison with the control samples. Especially this decline is very noticeable at energy values greater than E = E c -0.4 eV It should be noted that similar reduction of localized density in the semiconductor -dielectric boundary phase section [10] was observed in all aspects of the MIS structures, which was observed to decrease the rate of surface generation. In order to clarify this state, was determined change of the rate of surface generation using the formula (1) and (2) is shown in Fig. 5, whereas in the MIS structures the surface generated speeds in ultrasonic waves are relatively small compared to the test sample, and the transition time to the surface generator is significantly flattened. The spectral distribution of the density of surfaces along the silicon zone is almost unchanged after the ultrasound effect, so that ultrasound in metal-glass-semi-conductive structures leads to the change in the structure of glass layers at the boundary layer of the semiconductor glass separation. Separation of crystals in the glass content may lead to the decrease in the width and number of boundary phases, while the decrease in the rate of the external genera-tion and its time-varying variation. To investigate this hypothesis, the Al layer, which performs the chemo-electrode service from the MIS, has been removed and the surface layers of the anticholic vapors are removed. Then the microflora of the glass surface was obtained. Figure 6 shows the magnification of the glass surface of the two enlarged (2800 times) structures. Comparison of images suggests that, in ultrasound structures, the glass surface is less sensitive to a variety of additives and non-strangers.

Conclusion
Based on these results, when influenced at a frequency of 2.5 MHz, with a power of 0.5 W for 40 minutes, on the structures of Al-n-Si-glass-Al leads to a decrease in the integrated density of localized electronic states on the boundary of interphase of semiconductor -glass, and the surface electronic state of the semiconductor do not affect the energy spectrum, and the rate of surface generation decreases. Ultrasonic processing can lead to the improvement of the recombinative properties of the genera of the silicate glass and silicon boundary phase phase in the order shown.