Analysis of two kinds of chip luminescent layer structure design which can improve LED light efficiency

LDE's chip structure design is a very complex system engineering, which involves the design of electroluminescent structures for the purpose of improving injection efficiency and light efficiency, and the design of light extraction structures and optical effects. Electrode design, etc.

With the development of MOCVD epitaxial growth technology and multi-quantum well structure, people have made breakthroughs in precisely controlling epitaxy, doping concentration and reducing dislocations, and the internal quantum efficiency of the extended film has been greatly improved. Like the A1InGap-based LED with a wavelength of 625nm, the internal quantum efficiency is close to the limit, up to 100%. The internal quantum efficiency of the A1InGap-based LED is much lower than that of the A1InGap-based LED, but it is also 40% to 50%.

As we all know, the external quantum efficiency of LED depends on the internal quantum efficiency of the epitaxial material and the light-emitting efficiency of the chip. The key to improving the luminous efficiency of the LED is to improve the external quantum efficiency of the chip, which depends largely on the light-emitting efficiency of the chip. For this reason, HBLED and ultra-HBLED require a new chip structure to improve the light-emitting efficiency of the device, thereby improving the luminous efficiency. The following is a brief introduction to the technical approaches and developments to improve LED luminous efficiency.

Optimized chip luminescent layer band structure

Designing different luminescent layer structures can improve the luminous efficacy of LEDs. At present, there are two main types of luminescent layer structures:

One is double heterojunction (DH)

Heterojunction LEDs have semiconductor components with different band gaps in the P and N regions relative to the homojunction LED. In a heterojunction, the wide bandgap material is called a barrier layer, and the narrow bandgap material is called a well layer. The junction of only one barrier layer and the well layer is a single heterojunction (SH), and the junction of two barrier layers and one active layer (ie, the carrier composite luminescent layer) is called a double heterojunction. The two barrier layers of the double heterojunction act to limit the injected carriers, that is, the carriers that diffuse into the active layer through the first heterogeneous result surface will be negatively connected by the second heterojunction interface. Blocked in the active layer, so that the current HBLED band structure usually uses double heterojunction.

Second, the quantum well structure

The thinning of the active layer can effectively improve the radiation recombination efficiency and reduce resorption. However, when the thickness of the active layer can be compared with the de Broglie wave of electrons in the crystal, the carrier undergoes a change in the energy spectrum due to the quantum confinement. This particular structure is called a quantum well (QW). The carrier band in the potential well is no longer continuous, but takes a series of discrete values. The active layer can be either a single layer, ie a single quantum well (SQW), or a multilayer, a multiple quantum well (MQW) structure. The active layer using the quantum well structure can be thinner, resulting in further confinement of carriers, which is more conducive to efficiency. It has been found that the A1InGap double heterojunction LED with an emission wavelength of 565 nm has the highest light efficiency when the thickness of the active layer is in the range of 0.15 to 0.75 nm; when it exceeds this range, the light effect is drastically lowered, because the active layer is too Thin, it is easy to cause the carrier tunnel to penetrate outside the active layer; if the active layer is too thick, the carrier recombination efficiency will decrease. The quantum well structure is one of the widely used energy band structures of HBLED.

The following table lists the structure of the luminescent layer used in high-brightness LEDs currently used and their external quantum efficiency .