MQW Infrared Sensor on Silicon via Lattice Matching
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Solution Overview
Problem
Current infrared light detection technologies face challenges in mass production and cost-effectiveness due to limitations in substrate size and lattice mismatch ratios, making them unsuitable for widespread use in applications requiring sensitivity to near-infrared to mid-infrared wavelengths.
Innovation Solution
A solid-state imaging device utilizing a Multi-Quantum Wells (MQW) structure with a non-Group IV lattice matching-based compound semiconductor on a silicon substrate, featuring a Type II hetero interface and strain management through composition control, along with electron and hole barrier layers, to enhance sensitivity and reduce production costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an InP substrate is used for InGaAsSb based material MQW structure, then sensitivity to infrared light is achieved, but the substrate size is limited to 2-3 inches and cost increases to tens of thousands of yen per substrate
Solution Approach 1:
The patent changes the substrate material parameter from InP to Si, and adjusts the MQW material composition (InGaAsSb, InGaAs, GaAsSb) to achieve lattice matching with Si substrate. This parameter change enables use of large-size Si substrates for mass production while maintaining IR sensitivity through controlled material composition and quantum well structure design.
Solution Approach 2:
The patent introduces an InAlAs intermediate layer between the InGaAsSb MQW structure and the Si substrate. This intermediary layer serves as a buffer to accommodate lattice mismatch and dislocation reduction, enabling the integration of III-V compound semiconductor MQW structures onto Si substrates while maintaining both IR sensitivity and mass production capability.
2Productivity
If SiGe based material is used on Si substrate, then substrate area can be increased at low cost, but the lattice mismatch ratio is several percent which prevents thickening of the photoelectric conversion section
Solution Approach 1:
The patent employs composite material structures including InAlAs buffer layers, InGaAsSb MQW active layers, and InGaAs contact layers on Si substrates. This composite approach allows each layer to be optimized for its specific function while collectively managing the lattice mismatch issue, enabling both large substrate area utilization and controlled photoelectric conversion section thickness.
3Manufacturing precision
If compound semiconductor with lattice matching to Si substrate is used, then lattice mismatch ratio is reduced to less than 1%, but the band gap becomes wide (0.95 eV to 3.8 eV) which is not suitable for long wavelength infrared spectroscopy of 1.2 μm or more
Solution Approach 1:
The patent changes the band gap parameter by using quantum confinement effects in thin MQW structures. Although the bulk materials have wide band gaps suitable for lattice matching with Si, the quantum well confinement in nanoscale thickness (tens of nanometers) modifies the electronic structure to enable absorption at longer infrared wavelengths (1.2 μm and beyond) while maintaining lattice matching precision.
Solution Approach 2:
The patent transitions from bulk three-dimensional semiconductor materials to two-dimensional quantum well structures. This dimensional reduction creates quantized energy levels that adjust the optical absorption characteristics, allowing long-wavelength IR sensitivity despite the wide band gap of the lattice-matched materials on Si substrate.
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 solution enables sensitivity to infrared light across a wide wavelength range, from near-infrared to mid-infrared, while facilitating mass production and reducing costs by using a silicon substrate with a lattice mismatch ratio less than 1%, thereby improving the efficiency and affordability of infrared light detection.
Implementation Method 1
The MQW structure may have a Type II hetero interface and a thickness of each layer is set so as to form an inter-sub-band transition.
Implementation Method 2
there is a sensor with a photoelectric conversion section where an InGaAsSb based material is set to a Multi-Quantum Wells (MQW) structure on an InP substrate
Implementation Method 3
The hetero interface may apply compressive strain to ZnS1-X2SeX2 or CuIn1-Y2GaY2 (S1-X3SeX3)2 by controlling a Se composition or may apply compressive strain to GaP1-X4NX4 by controlling the N composition so as to cancel out tensile strain of FeS2 or Fe(S1-X1SeX1)2.
Data Source
AI summary
A solid-state imaging device includes a Multi-Quantum Wells (MQW) structure which combines and uses a non-Group IV lattice matching-based compound semiconductor with an absolute value of a mismatch ratio of less than 1% on a silicon substrate so as to have sensitivity to at least infrared light.