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thin films

The greatest interest represents a case of thin films. Dependence of a threshold voltage on a thickness for films of composition Ge2Sb2Te5 has been measured in operations [2S, 29]. It is gained, that the threshold electric field practically does not depend on a thickness of a film.

Similar effects for thin films of composition SiTeAsGe have been gained in operation [30].

Fig. 1.5. Dependence of a threshold electric field on temperature for a film of composition SiTeAsGe in the thickness 300 microns [30]

Dependence of a threshold voltage on a thickness for films of composition Ge2Sb2Te5 is shown on fig. 1.6. The points scored by triangular markers, are gained on svezhenapylennyh samples, and points scored by mugs are gained on samples, amorfizirovannyh from a crystalline phase by means of an electrical impulse. Corresponding dependence of a threshold voltage on temperature is given on fig. 1.5. It is visible, that in case of thin films dependence considerably less expressed, than in case of thick films.

Rice 1.6. Dependence of a threshold voltage on a thickness of a film of a composition

Ge2Sb2Te5 At a room temperature. The points scored by triangular markers, are gained on svezhenapylennyh films, points scored by round markers, gained on films, amorfizirovannyh by means of an electrical impulse [31].

It is obvious, that dependence of a threshold voltage on temperature for thin films essentially differs from a case of thick films. Also it is necessary to score, that in thin films quantity of a threshold electric field much more, than in case of thick films and feeblly depends on a thickness. It specifies that in thin films the switching effect is related to electronic processes

Experimental data are averaged on several samples. Exists more than ten models featuring nonlinearity BAX of disorder semiconductors in the strong electric field and a switching effect. To judge justice of each of models it is necessary to spend detailed comparison of deductions of model with the observational dependences. The majority of models of a switching effect have been developed only at qualitative level, to compare to experimental data it is possible only five models, developed quantitatively.

The thermal model will be compounded with experimental data on dependence of a threshold electric field on a thickness of a film and temperature for films in the thickness more than 10 microns. However in case of thin films qualitative distinction between effects of calculation and experimental data [32] is observed. Besides, according to thermal model quantity of conductivity in a threshold point approximately in 3 times
Differs from conductivity in the weaker sex. However on experiment the conductivity magnification 10 times and more is observed.

The phenomenological elektronno-thermal model well features nonlinearity Vakh, however the given model does not explain what processes can lead to exponential dependence of conductivity of an electric field [33, 34].

Fig. 1.7. Dependence of a threshold voltage on temperature for a composition film

Ge2Sb2Te5толщиной 30 nanometers [31]

For the model grounded on shock ionisation in a material about a 7/-minus by centres, detailed comparison with experimental data was not spent.

Also it is obvious, that the given model has some obvious deficiencies First, halkogenidnye stekloobraznye semiconductors have disorder structure, therefore the characteristic value of a free length in these materials of the order of a constant lattice. Secondly, in THIN films the threshold voltage is comparable with forbidden region breadth. At last, it is necessary to pay attention that injected in a material and electron defects recombine electrons in material volume. In thin films quantity of threshold density of a current is incremented and the volume in which there is a recombination decreases. For these parents the mechanism grounded on shock ionisation, is represented improbable.

The model grounded on pryzhkovoj of conductivity on localised states, well features high-resistance branch BAX and its temperature dependence [35].
However the model incorrectly features dependence of quantity of a threshold voltage and threshold density of a current from a thickness of a film [36]. To explain these dependences the model in which charged traps are casually proportioned on a material has been offered. In operation [37] model has been used for the description of a delay time of switching from quantity of the voltage, however the calculated dependence could not feature experimental data. Also it is necessary to pay attention that the guess of existence in HSP to the considerable concentration of the localised states contradicts many experimental data. It became a bottom for model making / a-minus of centres.

In [24] the model nukleatsii is explored and is shown, that the given model qualitatively features dependence of quantity of a threshold voltage on a thickness of a film and temperature, and also dependence of a delay time on temperature and quantity of the enclosed voltage. Also it is necessary to pay attention that the model nukleatsii explains only a switching effect, but cannot feature nonlinearity voltampernoj the performance.

Summing up it is necessary to score, that all existing models featuring nonlinearity voltampernyh of performances and a switching effect in HSP, have essential deficiencies. To draw a deduction on justice of each of models it is necessary to spend detailed comparison of predictions of model with experimental data. However by the present moment such comparison is spent not insufficiently full

1.3.

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A source: Baturkin Sergey Aleksandrovich. EXAMINATION of CURRENT PERFORMANCES HALKOGENIDNYH STEKLOOBRAZNYH of SEMICONDUCTORS of COMPOSITION GST-225 ALLOYED by NITROGEN And BOHR. The dissertation on competition of a scientific degree of the candidate of physical and mathematical sciences. Tver - 2015. 2015

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