The document discusses spin-based light-emitting diodes (spin-LEDs), which are semiconductor devices that emit light when an electric current passes through them, incorporating ferromagnetic electrodes to enable the emission of circularly polarized light. It covers the working principle of LEDs, the history and advancements in spin-LED technology, and their potential applications in medical imaging and optical communication networks. Additionally, the document highlights the importance of spintronics in enhancing the efficiency of these devices.

1. SPIN BASED LED
M.Uzair (17441510-099)
Maria Khizar (17441510-100)
Nayab Tahir (17441510-097)
Osama Munawar (17441510-098)

2.  A light-emitting diode (LED) is a semiconductor device that emits visible light
when an electric current passes through it. The light is not particularly bright, but
in mostly LEDs it is mono-chromatic, occuring at a signal wavelength. LEDs
convert electrical energy into light energy. They are frequently used as Pilot
lights in electronics appliances to indicate whether the circuit is closed or not.
What is LED?
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3. Working of LEDs
A P-N junction can convert absorbed light energy into a proportional electrical
energy. The same process is reversed here. The charge carriers recombine in a
forward-biased P-N junction as the electron cross from the N-region and
recombine with the holes existing in the P-region. Free electrons are in the
conduction band of energy levels, while holes are in the valence energy band.
Thus the energy level of the holes will be lesser then the energy levels of the
electrons. Some portion of energy must be dissipated in order to recombine the
electrons and the holes. This energy is emitted in the form of heat and light.
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5. History of spin -LED
 In 1999, the concept of a spin light emitting diode spin- LED was introduced, demonstrating the
ability to determine the degree of spin injection from a magnetic injector layer into the underlying
semiconductor LED structure by measuring the degree of circular polarization of the emitted light.
 The first significant demonstration of spin injection in a LED structure was achieved by
Fiederling et al with a II-VI DMS ferromagnetic injector on top of an AlGaAS/GaAS QW LED
structure .
 Significant advances have been made over the past decade toward efficient spin injection in spin-
LEDs.
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6. SPIN BASED LED
 A Spin-LED is a Light Emitting Diode structure spin-LED has ferromagnetic electrode
on the semiconductor LED structure. It can emit the circularly polarized
light Spin polarized electron injected from ferromagnetic electrode through atomic
barrier into the gallium arsenide with the semiconductor LED structure.
 The LED structure is typically a semiconductor hetero structure including an electron
reservoir (n-doped region) and a hole reservoir (p-doped region) separated by a lightly
doped "near" intrinsic semiconductor region.
 spin-injection from a ferromagnetic material into a semiconductor
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7. SPIN LEDS
 In recent years, a new field “spintronics”, that is an idea to use the spin of electrons in electronic
devices, progresses remarkably. whose quantum states can be controlled and operated using spin-
polarized carriers.
 We find that the electroluminescence circular polarization is at room temperature with the range of
values obtained from the QW spin –LEDs. of pure circular polarization electroluminescence at
room temperature with no external magnetic fields. They are obtained by electrically injecting
moderately high density of spins into semiconductor double hetero structures .
 A schematic experimental setup for EL measurements, showing, from upper left to lower right, a
wire-bonded rectangle spin-LED chip on a copper block, a quarter-wave plate (QWP), a linear
polarizer (LP), and a multi-channel spectrometer (MCS)
 Straight orange arrows accompanied by both-headed arrows represent light waves converted into
linear polarization by QWP. Thin dotted, blue arrows on polarizers represent optical axes.
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8. Continue…
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9. Pure CP (EL) WITH SPIN POLARIZED IED
 Ferromagnetic metals AlGaAs heterostructures with homogeneous and flat interfaces The electro-luminescence (EL)
from the light emitting diode (LED) consisting of the metal/insulator/semiconductor (MIS) structure depends on the
magnetization direction of the ferromagnetic electrode at room temperature. This fact shows that a spin-injection from
the ferromagnetic metal to the semiconductor is achieved.
 During the room-temperature electroluminescence (EL) with nearly pure circular polarization (CP) from GaAs-based
spin-polarized light-emitting diodes (spin-LEDs). External magnetic fields are not used during device operation.
 There are two small schemes in the tested spin-LEDs: firstly, the stripe-laser-like structure that helps intensifying the EL
light at the cleaved side walls below the spin injector Fe slab, and secondly, the crystalline AlOx spin tunnel barrier that
ensures electrically stable device operation. The purity of CP is depressively low in the low current density (J) region,
whereas it increases steeply and close To pure CP. right- or left-handed CP component is significantly suppressed
depending on the direction of magnetization of the spin injector.
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NAYYAB TAHIR
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NAYYAB TAHIR
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11. Working Principle
• A n-i-p semiconductor structure is a diode with a wide, lightly doped "near" intrinsic
semiconductor region between a p-type semiconductor and an n-type semiconductor
region. The p-type and n-type regions are typically heavily doped as they are used for
ohmic contacts. The addition of an intrinsic layer changes properties of the p-n junction.
• When reverse biased, a n-i-p diode enable the emission of light from the intrinsic region.
By energetically concentrating the radiative recombinations, the i-region reduces the
spectral enlargement emerging from the layers in-homogeneities. Compared to
conventional p-n diodes, the emitted wavelength is not submitted to a commonly
observed redshift when emission happens from a doped region.
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12. Cont.
• It is also possible to introduce a conned potential such as QWs or QDs in the intrinsic
region (Figure Shown). In addition of increasing the radiative recombination efficiency,
this gives an additional degree of freedom to modulate the emitted wavelength according
to the dimensions and strains of the QWs/QDs.
• When the diode is forward biased, the injected carrier concentration is typically several
orders of magnitude higher than the intrinsic level carrier concentration. Due to this high
injection level ( through depletion process) the electric field extends deeply into the
region.
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13. Cont.
• This electric field helps to speed up the transport of charge carriers from the P region to
the N region. This process results in faster operation of the diode making it a suitable
device for high frequency operations. When reversed biased, a n-i-p diode can be use as
an ultra-fast photo-detector with a bandwidth of several GHz.
• Indeed, the small carrier density in the intrinsic region provides a relatively long lifetime
to the photo-generated 𝑒−
− ℎ+
pairs by the reason of a low recombination probability.
This translates in a highly efficient photo-generation. Compare to conventional p-n
diodes, the wide intrinsic region makes the n-i-p diode an inferior rectifier (one typical
function of a diode). But, on the other hand, it makes the n-i-p diode suitable for
attenuators, fast switches, photo-detectors, and high voltage power electronics
applications.
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Figure: band structure of a n-i-p Spin-LED OSAMA MUNAWAR
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15. APPLICATIONS
• In the recent advance study, spin based LEDs (GaAs) can used in the early diagnosis of
Cancer.
• Now we are using MRI for the study of body organs. But spin based LED used for the
manufacturing of Optically Enhanced Nuclei Imaging.
• It can also be used in the Optical Communication Network ( Fiber Optics).
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