Nitride Semiconductor Laser P-Side Optical Guide Layer Design
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Solution Overview
Problem
Nitride semiconductor lasers face issues with increased threshold current, light leakage, and decreased internal quantum efficiency due to incomplete optical confinement and carrier overflow, leading to poor laser characteristics and high operating voltage.
Innovation Solution
A nitride semiconductor laser element with a structure that includes an n-type semiconductor layer, a p-type semiconductor layer, and an active layer with multiple well layers and barrier layers, where the p-side optical guide layer has regions with band gap energies lower and higher than the n-side optical guide layer, effectively reducing carrier concentration and non-radiative recombination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the p-side barrier layer thickness is increased to improve carrier confinement, then carrier overflow is reduced, but the operating voltage increases
Solution Approach 1:
The p-side optical guide layer is divided into multiple regions with different band gap energies: a first region adjacent to the active layer with lower band gap energy for voltage reduction, and a second region adjacent to the electron barrier layer with higher band gap energy for carrier confinement. This segmentation allows simultaneous optimization of both conflicting requirements.
Solution Approach 2:
Different regions of the p-side optical guide layer are assigned different local properties (band gap energies) to perform different functions: the first region provides low voltage operation while the second region provides strong carrier confinement. This local differentiation resolves the contradiction between voltage and confinement.
2Reliability
If the well layer thickness is increased to improve carrier confinement, then carrier overflow is reduced, but strain and piezoelectric polarization increase causing crystallinity deterioration
Solution Approach 1:
The invention optimizes the well layer thickness to 3 nm or less and adjusts the In composition ratio to 0.03 or more, maintaining the product relationship within specific ranges. These parameter changes enable sufficient carrier confinement while restraining strain accumulation and preserving crystallinity.
3Stability of the object's composition
If a composition graded layer is used in the n-side semiconductor layer to reduce strain, then crystallinity is improved, but voltage increases
Solution Approach 1:
The invention extracts the composition grading function from the n-side semiconductor layer and relocates it to the p-side optical guide layer. This allows the n-side layer to maintain uniform composition for low voltage operation, while strain management is handled by the graded regions in the p-side layer.
4Adaptability or versatility
If the In composition ratio in the well layer is increased to achieve longer oscillation wavelength, then oscillation wavelength extends toward green region, but strain and piezoelectric polarization increase causing internal quantum efficiency decrease
Solution Approach 1:
The invention establishes specific parameter ranges: In composition ratio of 0.03 or more, well layer thickness of 3 nm or less, and their product relationship. These parameter changes enable extension of oscillation wavelength toward the green region while restraining strain and piezoelectric polarization to maintain internal quantum efficiency.
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 structure enhances internal quantum efficiency and lowers operating voltage by reducing non-radiative recombination and improving optical confinement, resulting in improved laser characteristics and performance.
Implementation Method 1
The p-side optical guide layer includes: a first region that is disposed on a side of the final well layer and has band gap energy lower than that of the n-side optical guide layer, and a second region that is disposed on a side of the electron barrier layer and has band gap energy higher than that of the n-side optical guide layer
Implementation Method 2
carrier concentration in regions other than the well layer increases due to an increase of overflow of the carrier from the well layer, thus causing light absorption, non-radiative recombination (Shockley Read-Hall (SRH) recombination, non-radiative Auger recombination) or a radiative recombination not contributing to oscillation
Implementation Method 3
it has become possible for a nitride semiconductor laser as a nitride semiconductor element to perform oscillation in a wide wavelength range from an ultraviolet region to green
Data Source
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AI summary
To realize a nitride semiconductor laser element having improved internal quantum efficiency. The nitride semiconductor laser element includes an n-type semiconductor layer, a p-type semiconductor layer, and an active layer between the n-type semiconductor layer and the p-type semiconductor layer; wherein the n-type semiconductor layer includes an n-side optical guide layer; wherein the active layer includes two or more well layers, and at least one barrier layer provided between the well layers; wherein the barrier layer includes a barrier layer having band gap energy higher than that of the n-side optical guide layer; wherein the p-type semiconductor layer includes: an electron barrier layer having band gap energy higher than that of all barrier layers included in the active layer, and a p-side optical guide layer provided between a final well layer, that is a well layer nearest to the p-type semiconductor layer of the two or more well layer, and the electron barrier layer; and wherein the p-side optical guide layer includes: a first region that is disposed on a side of the final well layer and has band gap energy lower than that of the n-side optical guide layer, and a second region that is disposed on a side of the electron barrier layer and has band gap energy higher than that of the n-side optical guide layer.