Asymmetric DBR Layer Thickness for Optical Output Stability
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Solution Overview
Problem
The variability in crystal growth temperature leads to inconsistent DBR reflectance and optical output in optical semiconductor elements due to variations in the wavelength at which DBR reflectance becomes maximum, causing lot-to-lot variations in in-plane optical output.
Innovation Solution
The optical semiconductor element incorporates a distributed Bragg reflector with a pair of layers, where the first layer (AlxGa1-xAs) has a thickness larger than a quarter wavelength and the second layer (Inz(AlyGa1-y)1-zP) has a thickness smaller than a quarter wavelength, ensuring a phase difference of 180° at the center wavelength, which stabilizes the optical output by reducing film thickness variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a DBR with two layers of equal thickness (quarter wavelength each) is used, then the structure is simple and easy to manufacture, but the reflectance wavelength shifts significantly when crystal growth temperature varies, causing large lot-to-lot variations in optical output
Solution Approach 1:
The patent applies asymmetry by making the first layer thickness different from the second layer thickness. Specifically, the first layer has thickness d1 > λ0/(4n1) and the second layer has thickness d2 < λ0/(4n2), creating an asymmetric structure that compensates for temperature-induced wavelength shifts and reduces lot-to-lot variations in optical output.
2Reliability
If the DBR layer thicknesses are adjusted to compensate for temperature variation, then the optical output stability improves, but the manufacturing process becomes more complex and difficult to control
Solution Approach 1:
The patent applies parameter changes by modifying the thickness parameters of the DBR layers. The first layer thickness d1 is set greater than λ0/(4n1) and the second layer thickness d2 is set less than λ0/(4n2), where λ0 is the center wavelength. This parameter adjustment compensates for temperature variations during crystal growth and stabilizes the optical output without requiring complex additional structures.
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 the variation in relative reflectance and optical output across different lots, enabling stable production of optical semiconductors with reduced fluctuations in optical output characteristics.
Implementation Method 1
When a distribute Bragg reflector (DBR) is provided between a light emitting layer and a substrate, light directed from the light emitting layer toward the substrate can be reflected and high power infrared light can be emitted upward.
Implementation Method 2
A pair of a first layer and a second layer is periodically stacked in the distributed Bragg reflector. The first layer has a thickness larger than a quarter wavelength and the second layer has a thickness smaller than a quarter wavelength, ensuring a phase difference of 180° at the center wavelength
Data Source
AI summary
According to one embodiment, an optical semiconductor element includes a substrate, a light emitting layer, and a distributed Bragg reflector. The light emitting layer includes an AlGaAs multi quantum well layer. The distributed Bragg reflector is provided between the substrate and the light emitting layer. A pair of a first layer and a second layer is periodically stacked in the distributed Bragg reflector. The first layer includes AlxGa1-xAs. The second layer includes Inz(AlyGa1-y)1-zP. A refractive index n1 of the first layer is higher than a refractive index n2 of the second layer. The first layer has a thickness larger than λ0/(4n1) where λ0 is a center wavelength of a band on wavelength distribution of a reflectivity of the distributed Bragg reflector. The second layer has a thickness smaller than λ0/(4n2).