Hybrid Mirror VCSEL Structure for High Reflectivity and Lower Threshold
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Solution Overview
Problem
Current vertical cavity surface emitting lasers (VCSELs) face challenges in achieving high reflectivity, leading to increased threshold gain and current density due to the limitations of traditional distributed Bragg reflector (DBR) designs, particularly in reducing optical absorption loss and enhancing reflectivity across various semiconductor materials like GaAs, GaN, and InP.
Innovation Solution
A multi-junction bottom emitting VCSEL with a hybrid metal-semiconductor mirror structure, comprising a p-type semiconductor DBR, phase matching layer, and metallic reflector, is developed to increase reflectivity and reduce optical absorption loss, using materials such as Indium aluminum gallium arsenide on GaAs, GaN, and Indium phosphide substrates, thereby decreasing threshold current density and enhancing differential quantum efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional distributed Bragg reflector (DBR) designs are used, then the VCSEL structure is simple, but the reflectivity cannot reach greater than 99.9%, leading to increased threshold gain
Solution Approach 1:
The patent applies composite materials by combining metal reflector layers with semiconductor DBR layers to create a hybrid mirror structure. This composite approach achieves greater than 99.9% reflectivity by leveraging the high reflectivity of metals at specific wavelengths while using fewer total layers compared to pure semiconductor DBR designs, thereby resolving the contradiction between achieving high reflectivity and maintaining structural simplicity.
2Reliability
If more DBR pairs are used to increase reflectivity, then the reflectance increases, but the optical absorption loss increases and threshold current density increases
Solution Approach 1:
The patent changes the material composition parameter of the mirror structure by introducing metal layers with specific optical properties into the DBR stack. This parameter change allows achieving the required reflectance level with fewer total layers, thereby reducing the cumulative optical absorption loss that would occur in thicker pure semiconductor DBR structures, and consequently lowering the threshold current density.
3Reliability
If metal mirror is used as reflector, then the reflectivity can reach greater than 99.9%, but the threshold current density increases due to optical absorption
Solution Approach 1:
The patent segments the mirror function across multiple layers with different materials (metal layers and semiconductor DBR layers) rather than relying on a single material type. This segmentation allows each layer to contribute differently to the overall reflectivity while distributing the optical absorption characteristics, achieving high reflectivity with optimized current density performance.
Solution Approach 2:
By creating a composite hybrid mirror structure combining metal and semiconductor materials, the patent achieves superior optical performance where the metal provides high reflectivity at specific wavelengths and the semiconductor DBR layers provide broadband reflection and reduced absorption, collectively lowering the threshold current density compared to pure metal or pure semiconductor mirrors.
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 hybrid metal-semiconductor mirror structure achieves high reflectivity, reducing optical absorption loss and threshold current density while increasing output power and differential quantum efficiency across a broader range of semiconductor materials, addressing the limitations of traditional DBR designs.
Implementation Method 1
a hybrid metal-semiconductor reflector (110) disposed on the laser cavity... achieving high reflectivity, reducing optical absorption loss
Implementation Method 2
a n-type semiconductor distributed Bragg reflector (nDBR) (106) including a first plurality of layers of semiconductor material... a p-type semiconductor distributed Bragg reflector (pDBR) (110a) including a second plurality of layers of semiconductor material
Implementation Method 3
a phase matching layer (110b) disposed on the pDBR... achieving high reflectivity
Data Source
AI summary
Disclosed is a multi junction bottom emitting vertical cavity surface emitting laser (VC SEL) including: an electrical n-contact layer; a semiconductor substrate disposed on the electrical n-contact layer; an etch-stop layer disposed on the semiconductor substrate; a n-type semiconductor distributed Bragg reflector (nDBR) including a first plurality of layers of semiconductor material disposed on the etch-stop layer; a laser cavity having a plurality of active region disposed on the nDBR; a hybrid metal-semiconductor reflector disposed on the laser cavity; wherein the hybrid metal-semiconductor reflector is a p-type semiconductor distributed Bragg reflector (pDBR) including a second plurality of layers of semiconductor material, a phase matching layer disposed on the pDBR and a metallic reflector disposed on the phase matching layer; and an electrical p-contact layer formed on the hybrid metal-semiconductor reflector.