Ge PIN Photodetector Layout for Fast, High-Responsivity Detection
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Solution Overview
Problem
Photodetectors with heterojunction and homojunction structures face issues such as photocarrier accumulation at energy band discontinuities, leading to reduced response speed and optical responsivity, especially under high light intensity, due to ineffective absorption and weakened electric fields.
Innovation Solution
A photodetector design with a homojunction PIN structure that minimizes ineffective absorption by confining light between electrical polarity regions using a recess or protrusion in the light absorption layer, combined with a strong electric field application through biased electrodes, ensuring efficient photocurrent extraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a heterojunction structure with Si/Ge interface is used to achieve good light absorption in Ge photodetector, then optical responsivity is improved, but photocarrier accumulation occurs at the heterointerface causing response speed deterioration
Solution Approach 1:
The Ge light absorption layer is divided into three distinct regions along the light propagation direction: a Ge-n region with n-type doping, a Ge-i undoped region, and a Ge-p region with p-type doping. This segmentation allows the light absorption function to be separated from the charge carrier extraction function, preventing photocarrier accumulation at interfaces while maintaining effective light absorption in the undoped Ge-i region.
Solution Approach 2:
The undoped Ge-i region acts as an intermediary layer between the Ge-n and Ge-p regions. This intermediate undoped region prevents direct contact between oppositely doped regions, eliminating the formation of depletion layers at their interfaces and preventing photocarrier accumulation that would otherwise occur at heterojunction or homojunction interfaces.
2Reliability
If high concentration doping is used in Ge photodetector to enhance electrical conductivity, then carrier extraction efficiency is improved, but light absorption efficiency decreases due to free carrier absorption
Solution Approach 1:
Different regions of the Ge light absorption layer are assigned different doping characteristics tailored to their specific functions: the Ge-n and Ge-p regions have high doping concentrations optimized for carrier extraction and electric field formation, while the Ge-i undoped region has zero doping concentration optimized for light absorption. This local differentiation allows each region to excel at its designated function without compromising the other.
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 design achieves high optical responsivity and response speed by suppressing ineffective absorption and maintaining a strong electric field, thereby enhancing the photodetector's performance under varying light intensities.
Implementation Method 1
photodetectors that convert light into electric currents need to have an optical property of good light absorption
Implementation Method 2
Separation of the photocarriers, that is electrons and holes, is achieved by doping p-type impurities in the Si waveguide (Si-WG) connected to the Ge photodetector (Ge-PD) and by doping n-type impurities in the upper part of the Ge-PD
Implementation Method 3
This configuration is called a heterojunction vertical PIN structure because it has a heterointerface between Si and Ge
Implementation Method 4
The light absorption layer has a region having an effective refractive index higher than the rest of the light absorption layer between the first region and the second region
Data Source
AI summary
A photodetector has a substrate, a light input layer formed as a first semiconductor over the substrate, the first semiconductor being transparent to a wavelength being used, and a light absorption layer formed as a second semiconductor on the light input layer, the second semiconductor having a bandgap smaller than that of the first semiconductor. The light absorption layer has a first region doped with a first conductivity-type impurity, a second region doped with a second conductive-type impurity different from the first conductive-type impurity, and an undoped region between the first region and the second region. The first region, the undoped region and the second region are arranged in a direction parallel to the substrate. The light absorption layer has a region having an effective refractive index higher than the rest of the light absorption layer between the first region and the second region.