Thin Film AlGaInP LED with Same-Side Contacts
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Solution Overview
Problem
Conventional AlGaInP light emitting diodes (LEDs) face challenges due to thick semiconductor layers, which lead to tradeoffs between light absorption, electrical, and thermal resistivity, and require complex processing and substrate handling, limiting efficiency and reliability.
Innovation Solution
A thin film AlGaInP light emitting device is developed with a semiconductor structure where the growth substrate is removed, and n- and p-contacts are formed on the same side, utilizing a thin n-layer for lateral current distribution and a highly doped, thin p-type contact layer for vertical current conduction, eliminating the need for a thick transparent substrate and allowing for non-alloyed metal contacts with improved reflectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If thick semiconductor layers are used, then light absorption is improved, but electrical and thermal resistivity increase
Solution Approach 1:
The patent transitions from a conventional vertical LED structure with thick semiconductor layers to a planar flip-chip structure where contacts are formed on the same side. This dimensional reconfiguration allows current to spread laterally through a thin semiconductor layer, reducing vertical current path length and associated resistance while maintaining adequate light absorption through optimized lateral current distribution and enhanced light extraction geometry.
Solution Approach 2:
The patent changes the thickness parameter of the semiconductor layer from thick to thin, and reconfigures the contact geometry from opposite-side vertical injection to same-side planar contacts. This parameter change reduces the vertical current path length, thereby reducing electrical resistance and improving thermal conduction while maintaining device functionality through optimized lateral current spreading.
2Ease of operation
If thick transparent substrate is used, then current spreading is improved, but device complexity and processing difficulty increase
Solution Approach 1:
The patent extracts and eliminates the thick transparent substrate from the device structure, replacing it with a thin semiconductor layer that provides adequate current spreading through lateral current distribution. This extraction simplifies the device structure, reduces processing steps, and eliminates the need for substrate bonding while maintaining effective current spreading through optimized contact geometry and lateral current paths.
Solution Approach 2:
The patent employs a thin semiconductor film instead of a thick transparent substrate, utilizing the thin film's lateral current spreading capability to achieve effective current distribution. The thin film structure reduces device complexity, simplifies processing, and enables more efficient thermal and electrical performance while maintaining adequate current spreading through optimized contact configuration.
3Reliability
If conventional metal contacts are used, then electrical connection is achieved, but optical reflectivity is reduced due to alloying
Solution Approach 1:
The patent introduces a highly doped semiconductor contact layer as an intermediary between the metal contact and the active region. This intermediary layer provides excellent electrical connection through high doping concentration while maintaining high optical reflectivity by preventing direct alloying between the metal contact and the active semiconductor region, thereby preserving light extraction efficiency.
Solution Approach 2:
The patent changes the doping concentration parameter of the contact layer to be highly doped, which provides low electrical resistance for good electrical connection. Simultaneously, the thin thickness parameter of the contact layer is optimized to maintain high optical reflectivity by minimizing absorption while providing adequate electrical connection, thus resolving the trade-off between electrical performance and optical reflectivity.
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
This configuration reduces series resistance, minimizes absorption losses, enhances optical reflectivity, and simplifies fabrication, resulting in improved light extraction efficiency and thermal management while avoiding issues associated with wafer-level bonding and vertical injection structures.
Implementation Method 1
the interface between the p-type contact layer and the p-contact may be configured such that when the device is forward biased, carriers tunnel through the interface
Implementation Method 2
The top side of the semiconductor structure may be textured, roughened, or patterned
Data Source
AI summary
An AlGaInP light emitting device is formed as a thin, flip chip device. The device includes a semiconductor structure comprising an AlGaInP light emitting layer disposed between an n-type region and a p-type region. N- and p-contacts electrically connected to the n- and p-type regions are both formed on the same side of the semiconductor structure. The semiconductor structure is connected to a mount via the contacts. A growth substrate is removed from the semiconductor structure and a thick transparent substrate is omitted, such that the total thickness of semiconductor layers in the device is less than 15μm some embodiments, less than 10 μm in some embodiments. The top side of the semiconductor structure may be textured.