Quantum Cascade Laser Recess Electrode Current Spreading
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Solution Overview
Problem
Quantum cascade lasers with a ridge-type waveguide structure face challenges in achieving uniform electric field distribution due to non-uniform current spreading, which affects their performance and characteristics.
Innovation Solution
Incorporating a recess on the substrate's surface corresponding to the ridge portion, with a second electrode placed within the recess, reduces current spreading outside the ridge waveguide region, enhancing the uniformity of the electric field applied to the core layer by concentrating current flow within the ridge waveguide region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a ridge-type waveguide structure is used, then the device can be compact and low-cost, but the electric field distribution becomes non-uniform due to current spreading
Solution Approach 1:
a recess (50) which penetrates the back surface (10b) of the semiconductor substrate (10) in a region corresponding to the ridge waveguide region
Solution Approach 2:
The patent addresses the two-dimensional current spreading problem by introducing a solution in the vertical dimension (depth direction). By etching a recess into the substrate bottom surface, the invention creates a three-dimensional current path that guides carriers vertically into the ridge region, effectively controlling lateral current spreading through vertical structural modification
2Area of stationary object
If current is allowed to spread freely, then the active area is increased, but the electric field uniformity in the core layer deteriorates
Solution Approach 1:
The recess structure creates localized low-resistance regions specifically under the ridge waveguide, while the surrounding substrate maintains higher resistance. This spatially differentiated resistance distribution ensures current concentrates where needed (in the ridge region) without excessive spreading, achieving both adequate current conduction area and uniform electric field distribution
Solution Approach 2:
The recess acts as an intermediary structure that mediates between the electrode and the core layer. By providing a controlled low-resistance path through the recess, the invention intermediates the current flow to achieve uniform distribution in the core layer without direct contact between the electrode and the substrate surface
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 design improves the uniformity of the electric field, leading to better oscillation characteristics, reduced threshold current, and increased output, while also reducing end-facet leakage and enhancing mechanical strength and heat dissipation.
Implementation Method 1
The electrical resistance (hereinafter, referred to as the 'resistance') between the first electrode and the second electrode in the portion where the recess is provided is smaller than that in the portion where the recess is not provided
Data Source
AI summary
A quantum cascade laser includes a substrate having a first surface, a second surface opposite the first surface, and a recess provided in the second surface; a semiconductor region provided on the first surface of the substrate; a ridge portion extending in one direction on the semiconductor region; a first electrode provided along the ridge portion; and a second electrode provided on the second surface of the substrate. Furthermore, the semiconductor region includes a first cladding layer of n-type, a core layer, and a second cladding layer of n-type stacked in that order. The recess is provided at a position corresponding to the ridge portion in the second surface of the substrate, and the second electrode is provided in the recess.