Experimental Studies of Injection Electrolupinescence in P-N Junctions
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Date
1987-06
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Addis Ababa University
Abstract
. Experimental study of optical and electrical properttes of six
different g r o ups of electroluminescent diodes (LEOs) was carried OtK. at..
and near room temperatures. The first catego ry of the diodes consis t ed
of f our g r o u ps of red (LQ 1131). orange (experimental samples without
CA t alogue number) yellow I (LQ 1431) and green I (LQ 1731) colored LEOs
fa b r l catd by TESLA Elec t ronics, in Cze c hoslovaki n. Each o f t hese groups
cons i s t ed of seven samples. tn the second ca t egor y , t he re were t wo groups
o f ye llow n (LED4 586- 481) and green 11 (LED4 586- 491) c o lored LEOs each
with three samples. These second category LEDs were fab ric a ted by Ra d J 0
Spares (RS) of England.
Comparative studies of I-V. C-V. lphoto -v. e~is8ion spect r a a nd
band gap were carried out for all these diodes. The i -V characte r is tics
revealed that the ideality fector 'n' In [~ eqV / nKT range, from 1.3 ( {o r
orange) to 1.7 (for red) in the first four gr oups. For yel l ow II & green 11
this parameter has values of 1.8 & 1.9,respectively . These values of n
remained constant' in the exponential region which extended over about two
decades of the voltage for most of the diodes.
c-v result indicated that all the di odes have ab ru pt junct i ons with
built in potentials of 2.89. 1. 63. 2.04 , 2. 14, 1.92 & 2. 06 eV fo r red.
orange , yellow I, yellow II, green I & green II. respec t ive l y. The
lphoto VB V study showed that luminosity (- (photo) t'ias an exponential vol tage
dependence (of the fo rm eqV/rlKT) in the voltage range over wh ich t he
ideality factor (n) nea rly remained constant .
Emlssion intensity peaks were obse r ved for nil the. LEIJa Ilt wavelengths
(energies ) of 560 Obi (2.21SeV); 587 nil (2 . 114eV) ; 590 om
(2 . 10JeV); 662 om (1.874eV); 562 om (2.208eV) and 59) nm (2.092cV)
fo r g r een 1. yellow t. orange, red. green II and yellow II, respectively.
Spectra l emission s tudy and band gap meas urements showed that t.he LElls
are of Ga (As . P) with the eXceptIon of the orange LED!'J , whtch In sonte
cases showed deviations from the va lues of orange Ga (As.P) LEOs,
Radiative n!:combinations occured [or the red LEDs a t an impurity
level of about 50 MeV and [or green at about 40 MeV from either band
edge s . For yellow LElJs the values we r e as high .18 SU meV. An attempt was
made to evaluate efficiency of the ligh t emission fo r the EL diodes .
Light emission intens ity compari~on revealed red LEDs as t he mo~t intense
followed bv green I. the recombinat ion of which might have possib ly been
al'isisted by nit rogen i90electronic traps . The small intensity value in
all the rest of the diodes might be attribured to the absence of t he
isoelectronic trap~.
No position shift of the peak emission energy was observed wi th
diode currents for all the EL diodes .
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Keywords
Experimental Studies of Injection