Germanium Photodiode and JFET Structure for Low Dark Current
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing optical image sensors face challenges with high dark current and low optical fill factor due to poor interfaces and surface quality between semiconductor layers, which affect their performance and reliability.
Innovation Solution
The development of germanium-based photosensitive devices with a doped silicon layer between the germanium layer and the silicon substrate, along with a junction field effect transistor (JFET) and pinned photodiode passivation layer, reduces leakage current and improves optical fill factor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional optical image sensors are used, then manufacturing is simpler, but dark current is high and optical fill factor is low
Solution Approach 1:
An intermediate layer structure is introduced between the germanium photodiode and silicon substrate, consisting of a first interface layer (e.g., silicon oxide or silicon nitride) and a second interface layer (e.g., germanium sulfide or germanium selenide). This intermediary structure passivates interface states and reduces dark current by preventing direct contact between incompatible semiconductor materials, thereby resolving the contradiction between simplified manufacturing and improved dark current performance.
Solution Approach 2:
The patent employs composite material structures at the interface, combining multiple dielectric and semiconductor layers with different properties. The first interface layer provides basic passivation, while the second interface layer enhances optical coupling and further reduces interface states. This composite approach enables simultaneous improvement in dark current performance and optical fill factor without requiring complete redesign of the manufacturing process.
2Ease of manufacture
If germanium layer is directly contacted with silicon substrate, then manufacturing is easier, but interface quality is poor resulting in high leakage current
Solution Approach 1:
The first interface layer acts as an intermediary between the germanium layer and silicon substrate, providing a transition zone that maintains manufacturing simplicity while dramatically improving interface quality. This layer can be formed using standard deposition techniques and provides effective passivation of interface states that would otherwise cause high leakage current.
Solution Approach 2:
The patent modifies interface properties by introducing layers with different electrical and optical parameters. The first interface layer changes the electrical interface characteristics to reduce leakage, while the second interface layer optimizes optical parameters to improve fill factor. These parameter changes are achieved through controlled deposition processes that are compatible with existing manufacturing workflows.
3Reliability
If interface quality between semiconductor layers is poor, then manufacturing is simpler, but optical fill factor is low
Solution Approach 1:
The second interface layer is designed as a composite structure that addresses both optical and electrical requirements. Materials such as germanium sulfide or germanium selenide provide excellent optical matching between germanium and silicon, improving light coupling and fill factor. Simultaneously, this layer provides additional electrical passivation, maintaining low leakage current performance.
Solution Approach 2:
The interface structure is optimized locally at the germanium-silicon boundary where the most critical issues occur. The first and second interface layers are positioned specifically at this interface to provide targeted passivation and optical coupling enhancement, rather than requiring complex modifications throughout the entire device structure. This localized approach improves fill factor without excessive complexity.
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 significantly reduces leakage current, enhances optical fill factor, and improves conversion gain and noise performance, leading to better sensitivity and reliability in optical image sensors.
Implementation Method 1
a doped silicon layer disposed between the silicon substrate and the germanium layer
Implementation Method 2
a junction field effect transistor (JFET)
Implementation Method 3
pinned photodiode passivation layer
Data Source
AI summary
Germanium-based sensors are disclosed herein. An exemplary germanium-based sensor includes a germanium photodiode and a junction field effect transistor (JFET) formed from a germanium layer disposed on and/or in a silicon substrate. A doped silicon layer, which can be formed by in-situ doping epitaxially grown silicon, is disposed between the germanium layer and the silicon substrate. In embodiments where the germanium layer is on the silicon substrate, the doped silicon layer is disposed between the germanium layer and an oxide layer. The JFET has a doped polysilicon gate, and in some embodiments, a gate diffusion region is disposed in the germanium layer under the doped polysilicon gate. In some embodiments, a pinned photodiode passivation layer is disposed in the germanium layer. In some embodiments, a pair of doped regions in the germanium layer is configured as an e-lens of the germanium-based sensor.