MSM Heterojunction Diode for >100 THz Cut-off Frequency
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Solution Overview
Problem
Current diodes have limitations in cut-off frequency, typically below 10 THz, which restricts their operational speed and nonlinearity, making them unsuitable for high-speed applications such as optical frequency operations and energy conversion.
Innovation Solution
A metal-semiconductor-metal (MSM) heterojunction diode with a crystalline semiconductor layer thickness comparable to the mean free path of charge carriers, enabling near ballistic carrier transport and exceptionally high thermionic emission current density, along with degenerate doping for ohmic contacts, resulting in a cut-off frequency exceeding 100 THz.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a conventional diode structure is used, then the device is easy to manufacture, but the cut-off frequency is limited to below 10 THz
Solution Approach 1:
The patent changes the physical parameters of the semiconductor layer, specifically reducing its thickness to be comparable to or less than the mean free path of charge carriers (e.g., 1-100 nm range). This parameter change enables near-ballistic transport and dramatically increases the cut-off frequency from conventional <10 THz to >100 THz, while maintaining the basic MSM diode structure for ease of manufacture
Solution Approach 2:
The patent employs heterojunction structures combining different semiconductor materials (e.g., Si/SiO2, GaAs/AlGaAs, InP/InGaAs) with distinct band gaps and effective masses. This composite material approach optimizes carrier transport properties and enables high cut-off frequencies while maintaining structural simplicity and manufacturability
2Speed
If the semiconductor layer thickness is reduced to enable ballistic transport, then the cut-off frequency increases, but the current density must be maintained
Solution Approach 1:
The patent applies local quality by creating asymmetric doping profiles within the semiconductor layer, with different doping concentrations at opposite interfaces. This local variation in doping quality optimizes carrier injection at one interface while maintaining efficient collection at the other, ensuring high current density is maintained despite the reduced thickness enabling ballistic transport
Solution Approach 2:
The patent changes multiple parameters simultaneously: semiconductor layer thickness (to enable ballistic transport), doping concentration (to control carrier density), and material composition (to optimize effective mass and mobility). These coordinated parameter changes ensure that current density is maintained or enhanced while achieving the high carrier transport speeds necessary for >100 THz operation
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 MSM diode achieves exceptionally high cut-off frequencies, exceeding 100 THz, with low series resistance and excellent nonlinearity, facilitating efficient rectification and energy conversion at optical frequencies.
Implementation Method 1
A thickness of a crystalline semiconductor layer of an MSM diode is less than or comparable to a mean free path of charge carriers emitted into a semiconductor layer of the MSM diode, which can result in near ballistic carrier transport across the semiconductor layer
Implementation Method 2
near ballistic carrier transport across the semiconductor layer and lead to an exceptionally high thermionic emission current density
Implementation Method 3
exhibiting excellent nonlinearity and rectification
Implementation Method 4
forming a first metal layer overlying a first side of the crystalline semiconductor layer, forming a second metal layer overlying a second side of the crystalline semiconductor layer
Data Source
Figure 1~2d
Figure 3
Figure 4(a)~4(f)
AI summary
In one aspect, a diode comprises: a semiconductor layer having a first side and a second side opposite the first side, the semiconductor layer having a thickness between the first side and the second side, the thickness of the semiconductor layer being based on a mean free path of a charge carrier emitted into the semiconductor layer; a first metal layer deposited on the first side of the semiconductor layer; and a second metal layer deposited on the second side of the semiconductor layer.