Surface-Emitting Laser Current-Spreading Structure for Single-Mode Stability
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Solution Overview
Problem
Existing surface-emitting lasers using GaN-based materials face challenges in achieving uniform current injection density due to the high resistance of indium tin oxide (ITO) and p-GaN, leading to non-uniform gain distribution and instability in single-mode operation.
Innovation Solution
The surface-emitting laser incorporates a resonator with a first p-type semiconductor layer and a second p-type semiconductor layer with a larger band gap, along with a conductive layer that injects current into the active layer. The conductive layer contacts the first layer's surface and the interface between the first and second layers, facilitating uniform current distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a thin ITO layer is used to reduce light absorption, then light transmission is improved, but current injection uniformity deteriorates due to high lateral resistance
Solution Approach 1:
The patent transitions from two-dimensional current injection (through the thin ITO layer only) to three-dimensional current injection by adding vertical contact holes that penetrate through the ITO layer and p-GaN layer. This allows current to be injected from both the top surface and the bottom surface of the aperture region, achieving uniform current distribution without requiring a thicker ITO layer that would increase light absorption.
Solution Approach 2:
The patent introduces n-type semiconductor layers as intermediary conductive paths between the ITO layer and the active layer. These n-type layers with higher carrier concentration serve as mediators to facilitate uniform current distribution from the high-resistance ITO layer to the active layer, compensating for the lateral resistance of the thin ITO layer.
2Object-affected harmful factors
If ITO with high lateral resistance is used for current injection, then light absorption is reduced, but current spreads poorly in the lateral direction causing non-uniform current density
Solution Approach 1:
The patent segments the current injection path into multiple independent channels: (1) current injection through the ITO layer from the top, (2) current injection through the vertical contact holes from the bottom, and (3) current spreading through the n-type semiconductor layers. This segmentation allows each path to contribute to uniform current distribution without requiring any single path to have low resistance, thus maintaining both low light absorption and high current injection stability.
Solution Approach 2:
The patent creates a composite current injection structure combining transparent conductive oxide (ITO), highly doped n-type semiconductor layers, and vertical contact holes. This composite structure leverages the optical transparency of ITO and the high electrical conductivity of the n-type semiconductor layers to achieve both low light absorption and uniform current distribution.
3Power
If a large aperture diameter is used to increase output power, then more current is required, but non-uniform current density increases making single-mode operation difficult
Solution Approach 1:
The patent uses vertical contact holes to inject current from the bottom surface in addition to the top surface, creating a three-dimensional current injection pattern. This allows large aperture diameters to be used for high output power while maintaining uniform current density through the thickness of the laser structure, preventing the peripheral high-density/central low-density distribution that occurs with top-only injection.
Solution Approach 2:
The patent changes the electrical parameters of the semiconductor layers by introducing highly doped n-type layers with carrier concentrations of 1×10^19 to 1×10^21 atoms/cm³. This parameter change in carrier concentration creates low-resistance current paths that enable uniform current distribution across large aperture areas, allowing high output power with maintained single-mode operation.
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 achieves higher uniformity of current injection density within the resonator, reducing electrical resistance and enhancing single-mode properties by confining light laterally and lowering diffraction losses.
Implementation Method 1
a conductive layer through which a current is injected into the active layer of the resonator
Implementation Method 2
a resonator between the first reflector and the second reflector, the resonator including an active layer
Implementation Method 3
a second layer including a second p-type semiconductor layer having a second band gap larger than the first band gap, the second layer between the first layer and the active layer
Data Source
AI summary
A surface emitting laser includes: a first reflector; a second reflector; a resonator between the first reflector and the second reflector, the resonator including an active layer; and a conductive layer. The resonator further includes: a first layer including a first p-type semiconductor layer having a first band gap, the first layer having a first face contacting the conductive layer and a second face opposite to the first face; and a second layer including a second p-type semiconductor layer having a second band gap larger than the first band gap, the second layer between the first layer and the active layer. The second p-type semiconductor layer contacts the second face of the first layer. The conductive layer contacts at least a part of the first face of the first layer and an interface between the first layer and the second layer.