Asymmetric MSM Photodetectors for Low Dark Current Sensing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional MSM photodetectors face challenges in achieving low dark current densities, especially when using low bandgap semiconductor layers for long-wavelength light absorption, limiting their sensitivity and speed for optical communication systems.
Innovation Solution
The design incorporates an asymmetric metal-semiconductor-metal structure with different semiconductor materials for electron and hole Schottky junctions, allowing independent control of electron and hole current densities, and the use of graded semiconductor heterostructures to optimize Schottky barrier heights and reduce parasitic potential barriers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional symmetric MSM photodetectors use low bandgap semiconductor layers for long-wavelength light absorption, then sensitivity to long-wavelength light is improved, but dark current density increases significantly
Solution Approach 1:
The patent applies asymmetry by using different semiconductor materials for the n-type and p-type layers. Specifically, the n-type layer uses a material with a first bandgap while the p-type layer uses a material with a second bandgap, creating asymmetric Schottky barriers that independently control electron and hole injection. This asymmetric structure allows the detector to maintain high sensitivity to long-wavelength light while suppressing dark current through optimized barrier heights at each interface.
Solution Approach 2:
The patent implements local quality by tailoring the semiconductor material properties at different locations within the detector structure. The n-type and p-type layers use different semiconductor materials with specifically selected bandgaps to create locally optimized Schottky barriers. This local optimization allows independent control of electron and hole current densities, reducing overall dark current while maintaining sensitivity.
2Measurement precision
If conventional MSM photodetectors increase sensitivity through material selection, then detection capability is improved, but speed performance deteriorates
Solution Approach 1:
The patent applies parameter changes by systematically varying the bandgap parameters of the semiconductor materials used in the n-type and p-type layers. By selecting materials with specific bandgap values and adjusting the Schottky barrier heights through material composition control, the patent optimizes both sensitivity and speed parameters simultaneously. The independent control of electron and hole barriers allows tuning of carrier injection rates, directly affecting response speed while maintaining detection sensitivity.
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 approach significantly reduces dark current density and enhances sensitivity, achieving better performance than conventional MSM photodetectors, with a 28-fold reduction in dark current density compared to symmetric detectors, while maintaining high sensitivity and speed for optical communication applications.
Implementation Method 1
The semiconductor layer 10 has a bandgap small enough to absorb incident light in an operating spectral range, thereby exciting for each absorbed photon an electron from the valence band to the conduction band. A pair of free carriers is thus created: an electron in the conduction band and a hole in the valence band.
Implementation Method 2
In MSM photodetectors, the metal electrodes together with the semiconductor layer are configured to form Schottky junctions. A Schottky junction, also referred to as Schottky barrier or Schottky contact in the present description, is a potential barrier for electrons or for holes, formed at a metal-semiconductor interface.
Implementation Method 3
Schottky barriers have rectifying characteristics, suitable for use as a diode. Therefore, in a Schottky junction, for a positive bias voltage, the current increases exponentially with the voltage, while for a negative bias voltage, the current is almost constant with the voltage, provided the bias voltage is larger than a few k B T (thermal energy).
Data Source
Figure 1A~1B
Figure 2A~2B
Figure 3A~3B
AI summary
The present disclosure relates to a photodetector configured to detect incident light in a given range of wavelengths comprising: an absorbing semiconductor layer (325); a first semiconductor layer (321) made of a first semiconductor material and in electrical contact with said absorbing semiconductor layer; a first metal electrode (340) in electrical contact with the first semiconductor layer (321), configured to produce with the first semiconductor layer (321), an electron Schottky junction, wherein the first semiconductor layer is arranged between said first metal electrode and the absorbing semiconductor layer; a second semiconductor layer (322) made of a second semiconductor material different from the first semiconductor material, in electrical contact with said absorbing semiconductor layer; a second metal electrode (330) in electrical contact with the second semiconductor layer configured to produce with the second semiconductor layer, a hole Schottky junction, wherein the second semiconductor layer is arranged between said second metal electrode and the absorbing semiconductor layer.