Optical proprieties of pn junctions based on Si and the effect of proton beam and temperature Ahmed AKOUIBAA(1), Anouar JORIO(1), Izeddine ZORKANI(1
1 Solid
State Physics Laboratory, Faculty of Sciences, Dhar El Mahrez, B.P. 1796, Fes-Atlas, Morocco
Abstract The direct polarization of silicon PN junctions is accompanied by emission of light in the infrared. This emission is due to electron-hole recombination across the indirect gap. The reverse polarization is accompanied by a light emission in the visible. This phenomena is the subject of controversy since its discovery in 1955 by R. Newman. The main goal of this work is the study of the origin of the emitted light based on proton beam and temperature effect in Silicon, Gallium Nitride and gallium Arsenide nanostructured samples and their Schottky diodes.
Results and discussion In what follows, we presented the effect of some parameters such as temperature of hot electrons, the external temperature and energy of phonons and irradiation on the issue of our LED-based silicon. For polarization-line (Fig. 2) we note that the electroluminescence intensity decreases with the dose of proton irradiation to disappear for a fluence of 5x1013p/cm2. This issue is caused by radiative recombination of electrons from the conduction band and holes in the valence band across the indirect gap of Si (Eg = 1.1 eV).
In Figures 4 and 5, we show the temperature effect on electroluminescence spectra of EB junction bipolar transistors (npn). polarized live and avalanche respectively for a constant injection current. The intensity of electroluminescence spectrum (a) and decreased when the temperature rises from 307 K to 29 K. We also note that the structure (a) moves slightly towards higher energies when the temperature decreases.
Introduction Visible light emitted from Si PN junctions biased into avalanche generated a lot of research Most models proposed in the literature to interpret the spectra of electroluminescence (EL) obtained from the pn junctions in avalanche mode are based on transitions between the conduction band and valence band (interband models). To check its validity, we exposed junctions to radiation in order to introduce defects in the gap and we varied the temperature to change the gap and the population of carriers.
Experimental The results presented in this work are obtained from EB junction bipolar transistors commercial NPN (2N2219 A) manufactured by ST Microelectronics (Fig. 1), leaving the collector in the air. The light was observed in the case of reverse bias, it is yellow.
Fig.4 : Electroluminescence EB junctions of bipolar transistors (NPN) as a function of temperature at constant current, Forward bias.
Fig.2 : Electroluminescence EB junctions of bipolar transistors (NPN) as a function of photon energy at room temperature, forward bias.
But no change is produced in the spectral distribution of the spectrum (c), the decrease in EL intensity with temperature is due to increased non-radiative transitions.
The spectral composition of light emitted by the avalanche bias, illustrated in Fig.3, contains two structures is (b) and (c). We note that the intensity of electroluminescence signal corresponding to the structure (b) decreases when the dose of irradiation increases, but that corresponding to the structure (c) appears to be independent of irradiation fluence.
Fig.5 : Electroluminescence EB junctions of bipolar transistors (NPN) as a function of temperature at constant current, forward bias.
Fig.1 : Internal structure of the transistor after decapsulation, we see the EB junction. 1 mil= 24.5 μm
Conclusion To measure the signal of the integrated electroluminescence as a function of bias voltage, these junctions is biased in direct or reverse. The resulting signal is detected by a photomultiplier. The total intensity detected by the photomultiplier is measured by a pico-ammeter. The experimental spectra were taken at optical laboratory of the Department of Physics, University of Sherbrooke in Canada. Our samples were irradiated with 1 MeV proton linear accelerator at the Polytechnic University of Montreal in Canada with fluences ranging from 5x108 to 5x1013p/cm2
Fig.3 : Electroluminescence EB junctions of bipolar transistors (NPN) as a function of photon energy at room temperature, polarized avalanche.
If we believe in the physical reality of the independence of the structure (c) to fluences of irradiation and temperature, then the interband mechanism is not valid for explaining the origin of this emission, we ascribe this structure (c) transitions intra-conduction band.
References Energy structures (b1) and (b2) are less than the energy gap of Si (Eg = 1.1 eV). These structures can be attributed to inter-band recombination involving defects in the gap (acceptor and donor).
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