Photodiode Layer Structure for Low-Capacitance High-Speed Detection
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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 the undoped absorption layer contains a low concentration of carriers, limiting the thickness of the depletion layer and requiring higher bias voltages for sufficient depletion.
Innovation Solution
A semiconductor light-receiving element is designed with high-concentration and low-concentration layers of specific conductivity types, forming a PN junction interface, where the low-concentration layers have carrier concentrations less than 1×10^16/cm^3, allowing for a larger depletion area and reduced capacitance when a bias voltage is applied.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If an undoped absorption layer is thickened to reduce PN junction capacitance, then the element capacitance decreases, but the actual depletion layer becomes thinner when the entire layer cannot be depleted at the applied bias voltage
Solution Approach 1:
The patent changes the carrier concentration parameter of the absorption layer from undoped (intrinsic) to low-concentration doped (n-type or p-type with concentration of 1×10^17/cm³ or less). This parameter change allows the absorption layer to be fully depleted at lower bias voltages, ensuring that the entire thickened layer contributes to capacitance reduction without leaving undepleted regions.
2Ease of operation
If an intrinsic semiconductor layer is used as the undoped absorption layer, then it is easy to deplete the entire layer even at low voltage, but the layer actually contains a low concentration of carriers due to unintentional doping during epitaxial growth
Solution Approach 1:
The patent intentionally introduces a low concentration of carriers (n-type or p-type doping with concentration of 1×10^17/cm³ or less) during epitaxial growth to replace the uncontrolled unintentional doping. This controlled low-concentration doping achieves two goals: it maintains ease of depletion like intrinsic material while providing predictable and controllable carrier concentration for reliable device performance.
3Loss of energy
If the bias voltage is increased to increase the depleted area and reduce capacitance, then the capacitance decreases, but the available bias voltage is limited from the viewpoint of power consumption
Solution Approach 1:
The patent changes the carrier concentration parameter to very low levels (1×10^17/cm³ or less), which dramatically reduces the voltage required to deplete the absorption layer. This allows sufficient capacitance reduction to be achieved at low bias voltages, eliminating the need to increase voltage to reduce capacitance and thereby avoiding increased power consumption.
4Area of stationary object
If the carrier concentration in the absorption layer is reduced to increase the depleted area, then the depletion area increases, but the layer becomes more difficult to fully deplete when containing unintentional carriers
Solution Approach 1:
The patent precisely controls the carrier concentration parameter to be 1×10^17/cm³ or less through intentional low-concentration doping during epitaxial growth. This controlled low concentration ensures that the entire absorption layer can be fully depleted at practical bias voltages, achieving both large depletion area and complete depletion reliability, unlike higher concentration undoped layers that leave undepleted regions.
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 a large depletion area, low capacitance, and excellent high-speed responsiveness, even at lower voltages, improving power consumption and performance.
Implementation Method 1
a low-concentration layer of the first conductivity type and a low-concentration layer of a second conductivity type that form a PN junction interface, the low-concentration layer of the first conductivity type and the low-concentration layer of the second conductivity type each having a carrier concentration of less than 1×10^16/cm^3
Implementation Method 2
at least one of the low-concentration layer of the first conductivity type or the low-concentration layer of the second conductivity type including an absorption layer
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.