Light Detection Element with Dynamic Depletion Layer Control
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Solution Overview
Problem
Distance image sensors using silicon semiconductor substrates lack sensitivity to light with a wavelength of approximately 1.5 μm, and forming photogate and transfer electrodes on compound semiconductor substrates is challenging, while CMOS signal control is insufficient for high-speed indirect TOF schemes.
Innovation Solution
A light detection element with a semiconductor substrate, a light absorbing layer, a cap layer, and semiconductor regions forming a pn junction, where the depletion layer does not reach the light absorbing layer without bias but exceeds 50% of its thickness with a 20 V reverse bias, enabling high-speed signal output control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a silicon semiconductor substrate is used, then the device can be manufactured with existing processes, but sensitivity to light with a wavelength of approximately 1.5 μm is insufficient
Solution Approach 1:
The patent uses a compound semiconductor substrate (such as InGaAs or InP) that combines different semiconductor materials to achieve both high sensitivity to 1.5 μm light and compatibility with manufacturing processes. The composite structure allows the substrate to detect longer wavelengths while maintaining manufacturability through established semiconductor fabrication techniques.
Solution Approach 2:
The patent changes the material parameters of the semiconductor substrate by selecting compound semiconductors with appropriate bandgap energies that match the 1.5 μm wavelength detection requirement. This parameter change enables the substrate to absorb and detect infrared light at the target wavelength while still allowing for practical device fabrication.
2Reliability
If photogate and transfer electrodes are formed on compound semiconductor substrate, then sensitivity to 1.5 μm light is improved, but device complexity increases
Solution Approach 1:
The patent introduces an insulating layer as an intermediary between the compound semiconductor substrate and the photogate/transfer electrodes. This intermediate layer simplifies the electrode formation process by providing a suitable interface for depositing metallic electrodes on the compound semiconductor, reducing direct complexity while maintaining the sensitivity benefits of the compound material.
Solution Approach 2:
The patent divides the device into distinct functional layers including the compound semiconductor substrate, insulating layer, and electrode structures. This segmentation allows each component to be optimized independently - the compound substrate for sensitivity and the layered structure for manageable complexity in electrode formation and device fabrication.
3Device complexity
If CMOS is used for signal control, then integration is simplified, but control speed is insufficient for indirect TOF scheme
Solution Approach 1:
The patent implements dynamic control of the photogate electrode voltage to achieve high-speed signal output control required for indirect TOF schemes. By dynamically adjusting the photogate voltage in synchronization with the modulated light signal, the system achieves nanosecond-level control speed while maintaining the integration benefits of having the control circuitry integrated with the detector array.
Solution Approach 2:
The patent uses periodic modulation of the photogate electrode voltage at the same frequency as the transmitted light signal. This periodic action enables high-speed control by synchronizing the detection window with each modulation cycle, achieving the required control speed for indirect TOF while using integrated circuitry that can be implemented with CMOS-compatible processes.
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
Enables high-speed detection signal output with a simple configuration, improving sensitivity and responsiveness, particularly effective for detecting light with a wavelength of 1.5 μm, such as in fog or smoke environments.
Implementation Method 1
a depletion layer formed around the semiconductor region does not reach the light absorbing layer in a case where a reverse bias is not applied to the pn junction, and exceeds a position amounting to 50% of a thickness of the light absorbing layer from the cap layer side in a case where a reverse bias of 20 V is applied to the pn junction
Implementation Method 2
a light absorbing layer of a first conductivity type formed on the semiconductor substrate
Data Source
AI summary
A light detection element includes a semiconductor substrate, a light absorbing layer of a first conductivity type formed on the semiconductor substrate, a cap layer of a first conductivity type formed on the light absorbing layer, and a semiconductor region of a second conductivity type formed within the cap layer and forming a pn junction with the cap layer. A depletion layer formed around the semiconductor region does not reach the light absorbing layer in a case where a reverse bias is not applied to the pn junction, and exceeds a position amounting to 50% of a thickness of the light absorbing layer from the cap layer side in a case where a reverse bias of 20 V is applied to the pn junction.