Expermental Studies Of Injection Electroluhinescence In P-n Junctions
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Date
1987-06
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Addis Ababa University
Abstract
r·:xp~·cfment;}.1 ntudy of opttc:nl and electrical propert:t<~n of Blx
different groups of: ['lec.tJ:ulUin.i.ll.e~~Cl'fd:_ dl()d(~8 (LEDr.,) \.1<1£ (:;nried ottt.. at
and near roonl temperatures. The first category of the diodes consisted
of four groups of red (LQ 1131), orange (experimental samples «ithout
catalogue number) yello" I (LQ 1.431) and green I (LQ 1731) colored LEOs
fabricatd by TESLA ElectronIcs, in Czechoslovakia. E(1ch of theee groups
consisted of seven samples. In the second category, tllcre were two groups
of yelloH II (LEIl4 566-1,81) 8ml green II (L1l1J4 586-491) colored LEDs each
with three Romples. These sBcond category LEDs Here fabricated by Radio
Spares (RS) of England.
Comparative studies of I-V, C-V. lphoto -V, emission spectra and
band gap «ere carried out for all these diodes. The I-V characteristics
revealed that the ideality factoJ: 'n' In I."""qV/nKT ranges from 1.3 (for
orange) to 1.7 (for red) in the first four groups. For yellow II & green II
this parameter has values of 1.B & 1.9,respectively. These values of n
remained constant in the exponential region "hich extended over about tHO
decades of the voltage for most of the diodes.
C-·V resuLt indicated that all the diodes have abrupt junctions Idtll
built-in potentials of 2.89, 1.63, 2.04, 2.14, 1.92 f,. 2.06 eV for red,
orange, yelloH I, yellow II, green I & green II, respectively. The
I photo VB V study sho«.d that lUminosity ( ...... {photo) pas an exponential voltage
dependence (of the form eqV /rlKl") in the vol tage range over Hhieh the·
ideality factor (n) nearly remained condtant.
lengtl.s (energies) of 560 nm (2.215eV); 587 nm ~2.1L4eV); 590 nm
(?.103eV); 662 nrn (1.874eV); 562 nm (2.208eV) and 5931110 (l.092eV)
for green I, yello"¥Y I, orange, red, green II and yellow II, re8pecti~_ely.
Speetr"l emission ,'tudy and hand gap measurements sllOHed that the LElJs
are of Ga (As.P) >lIth the exceptIon of the orange LEOs, Hhich ill some
eases shm.,ed deviations from the values of orange Gn (As. P) LI<:Ds.
Radiative recombinations occured for the red ~ED9 at an impurity
level of about 50 maV and for green at about 1.0 meV f.rom either band
edges. r'or yellow LEDs the values wer" as high as 90 maV. An attempt Has
made to evaluate effIciency of the light emission for the EL diodes.
Light emission intensity comparison revealed red LEna as the most intense
folloHed by green I, the recombination of which might have possibly been
assisted by nitrogen isoelectrOtlic traps. The 'small intensity value in
all tIle rest of tIle diodes might be Bttribtlted to the absence of the
isoelectronic traps.
No pos1 tion shU t of the peak emission energy "as observed Hith
diode currents for all the EL diodes
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Keywords
Expermental Studies of Injection