Semiconductor Photodiode Internal Electric Field Optimization
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Solution Overview
Problem
Existing semiconductor photodiodes face inaccuracies in calculating the ratio of p-type absorption layers for maximizing response rate while maintaining light receiving sensitivity, due to assumptions about electron and hole drift velocities, especially under low reverse bias voltage and varying undoped absorption layer thickness.
Innovation Solution
A semiconductor photodiode design with a first undoped absorption layer and a p-type doped absorption layer of the same composition, where the first layer is depleted under reverse bias, and the second layer maintains electric charge neutrality, with a thickness ratio between 0.47 and 0.9, and optionally includes a semiconductor electron transit layer and field control layer to enhance carrier transit times.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the ratio of the p-type absorption layer is calculated using the general diffusion coefficient assumption, then the calculation is simplified, but the response rate optimization becomes inaccurate
Solution Approach 1:
The patent changes the parameter from using a general diffusion coefficient (De = 200 cm²/s) to using an effective diffusion coefficient that accounts for the internal electric field effect. This parameter modification allows the calculation to reflect the actual enhanced electron drift velocity caused by the internal electric field generated by hole-electron separation, thereby improving the accuracy of response rate optimization while maintaining the p-type absorption layer ratio calculation approach.
2Reliability
If the undoped absorption layer is made thick to improve light receiving sensitivity, then the drift velocity of holes decreases below saturation velocity, but the calculation accuracy deteriorates
Solution Approach 1:
The patent modifies the calculation approach by introducing the internal electric field effect into the drift velocity calculation. Instead of assuming constant saturation velocity (5×10⁶ cm/s), the patent calculates drift velocity as a function of the internal electric field strength, which varies with undoped layer thickness. This allows accurate determination of drift velocity even when it falls below saturation velocity, enabling optimal thickness design that maintains both sensitivity and calculation accuracy.
3Productivity
If the p-type absorption layer ratio is increased to maximize response rate, then the light receiving sensitivity is maintained, but the internal electric field effect becomes more significant
Solution Approach 1:
The patent incorporates the internal electric field effect into the response rate calculation framework by modifying the effective diffusion coefficient. This allows the calculation to automatically account for the enhanced electron transport caused by the internal electric field that arises when the p-type absorption layer ratio is increased. The modified calculation method captures the complex physical effects without requiring separate complex modeling, thus achieving accurate response rate prediction while considering the internal electric field.
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 achieves a higher response rate with maintained light receiving sensitivity by accurately accounting for internal electric field effects on hole drift velocity, leading to improved 3 dB cutoff frequencies and increased bandwidth.
Implementation Method 1
a light absorption layer which absorbs input light is disposed between a p-type contact layer connected to a p-type electrode and an n-type contact layer connected to an n-type electrode
Implementation Method 2
electrons generated in the p-type absorption layer are drifted to the undoped absorption layer through diffusion
Implementation Method 3
an internal electric field generated between the holes remaining within the undoped absorption layer and the electrons of the p-type absorption layer
Implementation Method 4
The electrons of the p-type absorption layer reach the inside of the undoped absorption layer at a velocity higher than a drift velocity calculated from the general diffusion coefficient De of the electrons by an internal electric field
Data Source
AI summary
Provided are a semiconductor photodiode which achieves a higher response rate in a state in which light receiving sensitivity is maintained. The semiconductor photodiode includes a p-type semiconductor contact layer, an n-type semiconductor contact layer, and a light absorption layer. The light absorption layer includes a first semiconductor absorption layer having a thickness Wd and a p-type second semiconductor absorption layer having a thickness Wp. The first semiconductor absorption layer and the second absorption layer are made of the same composition. The first semiconductor absorption layer is depleted, and the second semiconductor absorption layer maintains an electric charge neutral condition except for a region near an interface with the first semiconductor absorption layer. A relationship between the thickness Wd and the thickness Wp satisfies 0.47≤Wp/(Wp+Wd)≤0.9.