Semiconductor Light-Receiving Element With Graded Carrier Concentration
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Solution Overview
Problem
Semiconductor light-receiving elements face challenges in achieving a large depletion area and low capacitance for high-speed responsiveness, especially when using undoped absorption layers with unintentional carrier concentrations, which limit the thickness of the depletion layer and require higher bias voltages for sufficient depletion.
Innovation Solution
The semiconductor light-receiving element incorporates high-concentration and low-concentration layers of specific conductivity types, with carrier concentrations optimized to ensure depletion across the entire absorption layer, allowing for a larger depletion area and reduced capacitance, even at lower voltages, by forming a PN junction interface with low-concentration n-type and p-type InGaAs absorption layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If an undoped absorption layer is thickened to reduce PN junction capacitance, then the element capacitance decreases and high-speed responsiveness improves, but the actual depletion layer becomes thinner when the entire layer cannot be depleted at the applied bias voltage
Solution Approach 1:
The absorption layer is divided into multiple regions with different carrier concentrations: a first region with lower carrier concentration (1×10^15 to 1×10^16/cm³) and a second region with higher carrier concentration (1×10^16 to 1×10^17/cm³). This local differentiation allows the first region to be fully depleted for capacitance reduction while the second region provides sufficient carriers for practical operation, resolving the contradiction between depletion thickness and operational effectiveness.
Solution Approach 2:
The carrier concentration parameter is changed from uniform (traditional undoped or doped) to graded/non-uniform distribution within the absorption layer. By controlling the spatial distribution of carrier concentrations, the patent achieves both sufficient depletion in low-concentration regions for high-speed response and adequate carrier supply in high-concentration regions for practical operation.
2Area of stationary object
If the bias voltage is increased to deplete a larger area and reduce capacitance, then the depletion area increases and capacitance decreases, but the power consumption increases and the available voltage is limited
Solution Approach 1:
By creating regions with different carrier concentrations within the absorption layer, the patent enables different depletion characteristics in different areas. The low-concentration region depletes easily at low voltages, providing large depletion area and low capacitance without requiring high bias voltage, thus reducing power consumption while maintaining practical operability through the high-concentration region.
3Area of stationary object
If an undoped absorption layer with low carrier concentration is used to achieve large depletion area, then the capacitance is reduced, but the area that can be depleted is limited by the background carrier concentration
Solution Approach 1:
The absorption layer is structured with a first region having low carrier concentration (1×10^15 to 1×10^16/cm³) that can be fully depleted for large depletion area and low capacitance, and a second region with higher carrier concentration (1×10^16 to 1×10^17/cm³) that ensures sufficient carriers for reliable operation. This spatial differentiation of carrier concentrations resolves the contradiction between achieving large depletion area and ensuring depletion sufficiency.
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 enables a semiconductor light-receiving element with enhanced high-speed responsiveness and reduced power consumption, as the entire absorption layer can be depleted at a lower voltage, achieving a balance between large depletion area and low capacitance.
Implementation Method 1
a low-concentration layer of a second conductivity type configured to form a PN junction interface together with the low-concentration layer of the first conductivity type
Implementation Method 2
an undoped semiconductor layer, which is depleted when a bias voltage is applied under a use state and that serves as an absorption layer for an optical signal from an optical fiber
Data Source
AI summary
A semiconductor light-receiving element, includes: a semiconductor substrate; a high-concentration layer of a first conductivity type formed on the semiconductor substrate; a low-concentration layer of the first conductivity type formed on the high-concentration layer of the first conductivity type and in contact with the high-concentration layer of the first conductivity type; a low-concentration layer of a second conductivity type configured to form a PN junction interface together with the low-concentration layer of the first conductivity type; and a high-concentration layer of the second conductivity type formed on the low-concentration layer of the second conductivity type and in contact with the low-concentration layer of the second conductivity type. The low-concentration layers have a carrier concentration of less than 1×1016/cm3. The high-concentration layers have a carrier concentration of 1×1017/cm3 or more. At least one of the low-concentration layers includes an absorption layer with a band gap that absorbs incident light.