Carrier Trap Portion in Light Emitting Device
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Solution Overview
Problem
Group-III nitride semiconductor layers used in LEDs suffer from crystal defects like dislocations, which reduce internal quantum efficiency and crystal quality due to lattice and thermal mismatch with heterogeneous substrates, leading to non-radiative centers that trap carriers and hinder light emission.
Innovation Solution
Incorporating a carrier trap portion within the multi-quantum well structure with a band-gap energy decreasing from the periphery to the center, formed in the well layer, and using an aluminum-based barrier layer to generate tensile stress and offset compressive stress, along with an indium evaporation preventing layer to enhance crystal quality and light emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If Group-III nitride semiconductor layers are grown on heterogeneous substrates, then the device can be manufactured, but crystal defects such as dislocations occur due to lattice and thermal expansion coefficient differences
Solution Approach 1:
The patent introduces a buffer layer as an intermediary between the heterogeneous substrate and the Group-III nitride semiconductor layer. This buffer layer mediates the lattice and thermal expansion coefficient differences, reducing dislocation propagation while enabling device manufacturing. The buffer layer acts as a transition zone that protects the semiconductor layer from direct substrate-induced defects.
2Reliability
If a buffer layer is formed to prevent crystal defects, then dislocation propagation is reduced, but the active layer still has high density of crystal defects
Solution Approach 1:
The patent extracts harmful carriers that would otherwise be trapped by dislocations and redirects them to radiative recombination centers. By removing the harmful effect of dislocation-trapped carriers through the carrier trap portion design, the system converts non-radiative centers into radiative centers, improving light emission efficiency despite the presence of crystal defects.
Solution Approach 2:
The patent introduces localized carrier trap portions within the active layer that have specific energy levels tailored to capture carriers that would otherwise be lost to dislocations. These localized structures provide different functional properties at specific positions within the active layer, creating preferential recombination paths that bypass defect regions.
3Loss of energy
If carriers are trapped by dislocations in the active region, then internal quantum efficiency deteriorates, but light emission is hindered
Solution Approach 1:
The patent converts the harmful effect of dislocations into a beneficial mechanism by designing carrier trap portions that actively capture carriers that would otherwise be lost. The dislocation regions, which normally cause non-radiative recombination, are transformed into sites that guide carriers toward radiative recombination through the engineered carrier trap portions, thereby converting energy loss into useful light emission.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The carrier trap portion effectively traps carriers that would otherwise be lost to dislocations, improving internal quantum efficiency and crystal quality by converting non-radiative centers into radiative centers, thereby enhancing light emission efficiency.
Implementation Method 1
at least one carrier trap portion formed therein, the at least one carrier trap portion having a band-gap energy decreasing from a periphery of the carrier trap portion to a center of the carrier trap portion
Implementation Method 2
using an aluminum-based barrier layer to generate tensile stress and offset compressive stress
Implementation Method 3
The active region may have a single quantum well structure having a single well layer or a multi-quantum well structure having multiple wells and barrier layers. The multi-quantum well structure may include InGar-well layers and GaN-barrier layers alternately stacked on top of each other
Data Source
Figure 1~2
Figure 3
Figure 4(a)~4(c)
AI summary
A light emitting device can be used for light emitting diodes and laser diodes. The light emitting device includes a substrate, a first semiconductor layer on the substrate, a second semiconductor layer on the first semiconductor layer, and a multi-quantum well structure including at least one well layer and at least one barrier layer between the first and second semiconductor layers. A carrier trap portion is formed in at least one layer within the multi-quantum well structure. The carrier trap portion has a band-gap energy that gradually decreases from a periphery of the camlet trap portion to a center thereof.