All sciences. №9, 2023. International Scientific Journal - страница 4

In Fig.2. The spectral dependences of the short-circuit current (Icz) of the CdTe layer for various values of the corona discharge intensity, which were carried out by contact (2) and electric probe contact (3) to the surface of the CdTe semiconductor, are presented. It can be seen that in the absence of external influences in the Icz (v) spectra, an inversion of the Icz sign is observed in the vicinity of the light quantum energy value equal to hν= 1.21eV (curve 1) the inclusion of the surface corona discharge potential between the CdTe layer and silicon leads to a significant change in the spectral sensitivity of the short-circuit current (Icz). When the surface potential changes within its value from 0 to 100 V, the inversion position of the short-circuit current sign will mix into the short-wave region of the spectrum. In this case, the maximum photosensitivity of the Icz will be mixed into the short-wavelength region of the spectrum in the range from 0.93 eV to 1.5 eV. The position of the maximum value of the Icz increases by more than 1000 times at 70 angstems (curve 3).

Fig.2. Spectral dependences of the Icz for the CdTe-SiO2-Si structure on the magnitude of the corona discharge potential: jcr = 0 V (curve 1), 40 V (2),70 V (3). The inset shows the photosensitivity spectra of the impurity region of light absorption on a logarithmic scale.

For a qualitative description of the physical nature of the transfer phenomenon occurring in the CdTe – SiO2 – Si (semiconductor – oxide – semiconductor, i.e. POP) structure when a voltage is applied to it, consider a model in which a stationary current consists of a stream of electrons tunneling from the conduction band of a semiconductor into a deep level located in the oxide (and including the trap at the interface). Since the thickness of the silicon oxide in the structure under consideration is 0.4 microns, according to our estimates, the first contribution to the total flow is insignificant (less than 25%).

Tunneling of current carriers from the CdTe film into deep levels of silicon oxide leads to a change in the filling of the surface state. The latter, depending on the magnitude of the built-in charge, modifies the potential relief of the structure. So that the photogeneration rate will depend on the magnitude of the built-in charge, i.e. on the magnitude of the corona discharge potential in the structure. This means that the magnitude of the photo-EMF will be determined by the degree of asymmetry of the potential relief.

For a qualitative description of the physical nature of the kinetic phenomenon in the structure of semiconductor CdTe – oxide semiconductor SiO2 – semiconductor Si, a model based on the theory of a TIR (metal-dielectric-semiconductor) transistor can be considered. In this case, we mean that in a thick (0.4 µm) oxide layer, the main mechanism of current flow is determined by the Fowler – Nordheim model [5] and the corresponding current is denoted as

where i is the emission current density, E is the electric field strength, φ is the output operation, functions a and b depend on the geometry and operation of the output, for example, the degree of asymmetry, height, and width of the potential barrier. The current carrier flow should occur: a) due to the increasing (due to the Poole-Frenkel effect) thermionic emission through the potential barrier (jFN) of electrons with an increase in the magnitude of the corona discharge potential, b) due to the autoelectronic emission of current carriers trapped in the semiconductor oxide into the CdTe (jFN) conduction band. Since the contributions to the total current from the above currents are different in magnitude, the continuity of the current is disrupted at the interface. Thus, the excess (nonequilibrium) current carriers that appear in this case lead to the accumulation of charge at the interface. This leads to a redistribution of the internal electric field, which is essential in the formation of a potential barrier relief.