Lateral Ge PIN Photodiode for High Bandwidth Low Voltage Operation
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Solution Overview
Problem
Current Ge-PIN photodiodes face challenges in achieving high optical bandwidth and sensitivity simultaneously at low operating voltages, with existing solutions either requiring high voltages for high sensitivity and bandwidth or compromising on bandwidth for sensitivity.
Innovation Solution
A Ge PIN photodiode with a lateral arrangement of n-doped, intrinsic, and p-doped germanium regions, where the doping fronts are parallel and extend to the waveguide, and homogeneously doped silicon or silicon-germanium extensions cover the germanium region laterally, enabling a straight electric field profile and reducing metal-germanium contact, thus optimizing bandwidth and sensitivity at low voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If direct metal contact with highly doped Ge regions is used, then ease of manufacture is improved, but sensitivity deteriorates due to light absorption losses
Solution Approach 1:
The patent introduces an intrinsic Ge region as an intermediary between the metal contact and the light-sensitive intrinsic Ge region. This intermediary structure allows metal contact to be made through doped Ge regions without direct contact between metal and the light-sensitive area, thereby maintaining ease of manufacture while preventing light absorption losses that would reduce sensitivity.
2Productivity
If high operating voltage is applied, then bandwidth and sensitivity are improved, but dark current increases and circuitry complexity worsens
Solution Approach 1:
The patent changes the structural parameters of the Ge region by creating a lateral arrangement with specific doping profiles and extending doped regions to the waveguide interface. This structural parameter change enables the diode to achieve high bandwidth and sensitivity at lower operating voltages, thereby reducing dark current and simplifying circuitry requirements without sacrificing performance.
3Productivity
If intrinsic region width is reduced to increase bandwidth, then bandwidth is improved, but sensitivity deteriorates
Solution Approach 1:
The patent transitions from a vertical optimization approach to a lateral arrangement, extending doped Ge regions laterally to the waveguide interface. This dimensional change allows the intrinsic region to maintain sufficient width for high sensitivity while achieving high bandwidth through the lateral field distribution and reduced depletion region curvature, decoupling the trade-off between these two parameters.
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 solution allows for high optical bandwidth and sensitivity at acceptably low operating voltages, avoiding the limitations of previous designs by maintaining a non-curved electric field profile and minimizing light absorption losses.
Implementation Method 1
Modern photo detectors use germanium (Ge) as a detector material due to its significantly better absorption capacity than silicon in the wavelength range used for optical communication
Implementation Method 2
losses due to light absorption by free charge carriers in the doped Ge regions
Data Source
Figure 1
Figure 2
Figure 2a
AI summary
A diode is described comprising a photosensitive germanium region (5) located on a silicon or silicon-germanium waveguide (2). The diode has lateral dimensions that are identical to, or at most 20 nm shorter per side than, the waveguide in a direction perpendicular to the direction of light propagation in the waveguide. The germanium region of the diode contains a lateral arrangement of an N-doped (5b), an intrisic (5), and a P-doped (5a) germanium region. Furthermore, the P- and N-doped regions (5a, 5b) within the germanium region are laterally connected to additional homogeneously doped extensions (6a, 6b) of silicon or silicon-germanium, which extend vertically at least to a level equal to the highest point of the germanium region (5) in the vertical direction.