Taiwan's Recent Research Higher Luminous Efficiency InGaN Green LED Grow Conversion Process

Referred to as a light emitting diode LED. The gallium (Ga) and arsenic (AS) diodes , phosphorus (P) compounds made ​​when the electron and hole recombination can radiate visible light , which can be used to make light-emitting diodes. LED is called the fourth generation light source , energy saving, environmental protection, safety , long life, low power consumption, low heat , high brightness , waterproof, micro, shockproof , easy dimming, beam focus , easy maintenance , etc. , can be widely used various directions, display , decoration , backlight, general lighting and other fields. Among them, indium gallium nitride (InGaN) - near ultraviolet , blue, green, and blue .

National Cheng Kung University in Taiwan has used indium gallium nitride growth process developed nearly green LED, which makes the device a peak external quantum efficiency reached 48.6% . The process involves the conversion of indium nitride and gallium nitride grown in 2 seconds burst (bursts) when .

Green LED light to enhance effective way many researchers are exploring . Currently, the production of highly efficient LED still not ideal material because yellow-green band (gap) is present in red-orange and indium gallium nitride arsenide / phosphide devices between blue visible spectrum .

This LED material growth in the Thomas Swan 19x2 -inch dense with spray head (CCS) MOCVD system patterned sapphire substrate. CCS technology is owned by AIXTRON . Diameter sapphire pattern is 3.5μm, the cone angle of the array gap of 2μm . Pyramid height of 1.3μm.

Organic metal nitride semiconductor epitaxial source trimethyl gallium , trimethyl indium and trimethyl aluminum (TMG, TMI, TMA) and ammonia ((NH3), nitrogen gas . InN / GaN transformation ( Figure 2 ) is the active light emitting region a multiple quantum well (MQW) executed. conversion loop comprising the TMG and TMI 40 seconds burst ring ammonia gas is maintained constant. researchers have grown in the wells of a standard production of TMG and TMI constant MQW (LED I).

The epitaxial material and X-ray analysis showed PL , InN after conversion / GaN growth wells (LED II) better crystal quality . LEDII PL FWHM of the (FWHM) of 24.6nm, LEDI of 29.1nm. also show x-ray , LED II is 89 arcsec, LED I is 93.5 arcsec. With wider peak (satellite peaks) with increasing surface roughness or alloy composition changes related.

When the injection current is less than 120mA, LED I forward voltage of 3.35V, while the LED II was 3.34V. In -15V when , LEDI reverse leakage current 53.7μA, LEDII to 5.1μA. Its current and voltage curves shows that by the ideal factor (ideality factor) measurements that , LEDII reduced non- radiative recombination , non-radiative recombination will reduce the luminous efficiency.

The researchers believe that a better ideal factor and reduce the reverse current leakage , due to LEDII transformed InN / GaN growth process in green InGaN / GaN MQW crystal quality improvements.

Electroluminescent (EL) light output and external quantum efficiency (EQE) data confirm the ideal reverse current leakage factor and the expected ( Figure 3 ) . When 120mA, LED I and II of the optical output power of 89.5mW and 110.2mW. Respective EQE were 30.8% and 37.9% . LED II peak EQE of 48.6%, LED I was 34.0 %.

Lack of LED II is when the light fades 350mA peak of 44.6% . LEDI , compared with 30.7%.

The researchers also studied the problem of blue shift and FWHM of EL spectra . The study showed , LEDII crystal quality improvement to enhance the polarity of the electric field stress mutagenesis (strain-induced polarization field), which also resulted in greater quantum confinement Stark effect (QCSE), QCSE electrons and holes are large electric field to separate , lower light. The researchers said , which leads to the emission wavelength of the blue LED II drift and bad light than LED I great.


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