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Negative luminescence from InAsSbP based diodes in the 4.0-5.3 µm range

Generation and recombination of carriers in p- and n-sides of a p-n junction govern a reverse current in the LEDs. That’s why one can expect that electrons and holes may be efficiently extracted from p-n junction vicinity with subsequent concentration fall well below equilibrium values. The extraction means that n*p<no po=ni2 where n, p, and no, po refer to non-equilibrium and equilibrium concentrations respectively and ni is the intrinsic concentration. This results in the net absorption of ambient blackbody (BB) radiation, that is, the material can absorb more radiation than it emits which is equivalent to lower effective device temperature. Thus, the reverse biased (RB) device work as a “light absorbing diode” (LAD) with corresponding phenomena known as a “negative luminescence” (NL).

NL intensity grows on both wavelength and temperature (T) increase which reflects the BB radiation properties. However, this is not the case for the FB LEDs because Auger recombination strongly enhances with energy band gap and (1/T) decrease. There is, thus, a “crossover temperature” which indicates the starting point of superiority of NL efficiency over that of FB LEDs. Fig.1 presents experimental and simulated data relative to determination of the “crossover temperature” in the 20-180oC range: best room temperature (RT) LED outputs taken from literature and expectations of LED power at high temperatures obtained through the experimental power quenching coefficient. There is a lot of enthusiasm for NL devices with wavelengths longer than 4 mm since the “crossover temperature” is only 60 and 100-120oC for 6 and 4.3 mm LEDs correspondingly. So, NL LED operation at elevated temperatures can thus bring more benefits than conventional forward bias (FB) operation mode.

Fig.2 presents FB  triangle diode image recorded by CdHgTe (77 K)  (l =3-5 mm) based thermal camera at 55oC (by Prof.Malyutenko V.K., Kiev).  The image  reflects the drop of a signal at the contact (green area at the triangular center) and the signal decreasing from center to edge (in FB mode) i.e. an evidence for current crowding.

In contrast to Fig.2 the negative luminescence image (Fig.3)   “inherits” some of the positive luminescence peculiarities: small signal at the contact. However, the apparent temperature distribution is nearly uniform. That is because of the increase of resistance of a p-n junction in a reverse bias.

Additional information on negative luminescence devices can be found in publications. including our overview (pdf in Russian) 


NL expectation.gif (5095 bytes)


PL image.gif (18746 bytes)


NL image.gif (31843 bytes)