Sep 21, 2015


A quantum well is a potential well with only discrete energy values.
One technology to create a quantum well is to confine particles, which were originally free to move in three dimensions, to two dimensions, by forcing them to occupy a planar region. The effects of quantum confinement take place when the quantum well thickness becomes comparable to the de Broglie wavelengthof the carriers (generally electrons and holes), leading to energy levels called "energy subbands", i.e., the carriers can only have discrete energy values.
Quantum wells are formed in semiconductors by having a material, like gallium arsenide sandwiched between two layers of a material with a wider bandgap, likealuminium arsenide. (Other example: layer of indium gallium nitride sandwiched between two layers of gallium nitride.) These structures can be grown by molecular beam epitaxy or chemical vapor deposition with control of the layer thickness down to monolayers.

Thin metal films can also support quantum well states, in particular, metallic thin overlayers grown in metal and semiconductor surfaces. The electron (or hole) is confined by the vacuum-metal interface in one side, and in general, by an absolute gap with semiconductor substrates, or by a projected band gap with metal substrates.

For blue or green LED wafer, the structure is grown on sapphire substrate by MOCVD, which is called hetero epitaxy. Though homoepitaxy on Gallium Nitride substrate is more efficient, few manufacturers perform it due to high cost of substrate. Its quantum wells is composed of InGaN/GaN to adopt to mitigate the QCSE. and the quantity should be 6-12 pairs, and the structure should be as the following:

Structure layers
InGaN/GaN(active area)
u- GaN
Al2O3 (Substrate)

In conven However, this inevitably increases the carrier density in quantum wells, which in turn aggravates the Auger recombination, since the Auger recombination scales with the third power of the carrier density. As a result, the efficiency droop of the Auger recombination severely limits the LED performance. Here, we proposed and showed wide InGaN quantum wells with the InN composition linearly grading along the growth orientation in LED structures suppressing the Auger recombination and the QCSE simultaneously. Theoretically, the physical mechanisms behind the Auger recombination suppression are also revealed. The proposed LED structure has experimentally demonstrated significant improvement in optical output power and efficiency droop, proving to be an effective solution to this important problem of Auger recombination.

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