Predisposed HEMT Continuous Cap Layer State Selection
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Solution Overview
Problem
The fabrication of high electron mobility transistors (HEMTs) requires cost-effective and simple methods, as traditional FETs face challenges with impurity-induced carrier slowdowns due to doped channels, which are avoided in HEMTs using non-doped channels and two-dimensional electron gas sub-layers, but complex segmentation of cap layers is necessary for state selection.
Innovation Solution
A predisposed HEMT structure with a buffer layer, HEMT channel layer, and HEMT cap layer having a continuous surface, where bandgap and polarization differences between layers select the ON or OFF state without the need for segmenting the cap layer, simplifying fabrication by allowing the cap layer to maintain a continuous surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the HEMT cap layer is segmented to select ON or OFF state, then the state selection control is improved, but the fabrication complexity increases
Solution Approach 1:
The patent changes the electrical parameters (doping type and concentration) of different regions within the continuous HEMT cap layer to create predisposed states. The gate region has different doping characteristics than the source and drain regions, allowing electrical state selection without physical segmentation. This resolves the contradiction by maintaining fabrication simplicity while achieving operational control through parameter variation rather than structural division.
2Quantity of substance
If traditional doped channels are used to provide carriers, then the carrier provision is improved, but the electron mobility decreases due to impurity collisions
Solution Approach 1:
The patent introduces an intermediary mechanism where the HEMT cap layer with its specific doping structure creates a two-dimensional electron gas at the interface with the channel layer. This 2DEG serves as the carrier source, mediating between the doped cap layer and the non-doped channel to provide high carrier concentration without impurity scattering in the channel itself, thus resolving the contradiction between carrier provision and electron mobility.
Solution Approach 2:
The patent applies local quality by concentrating the doping in the HEMT cap layer while keeping the channel layer non-doped. This creates a localized carrier generation region that supplies electrons to the channel without contaminating it with impurities. The spatial separation of doping function (in cap layer) from conduction function (in channel layer) resolves the contradiction between needing carriers and maintaining high mobility.
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 simplifies the fabrication process by eliminating the need for complex cap layer segmentation, enabling reliable and cost-effective production of both normally ON and OFF HEMTs with high electron mobility.
Implementation Method 1
a bandgap difference and a polarization difference between the HEMT channel layer and the first HEMT barrier layer attracts available carriers, such as electrons, in the first HEMT barrier layer into the HEMT channel layer
Implementation Method 2
a bandgap difference and a polarization difference between the HEMT channel layer and the first HEMT barrier layer attracts available carriers, such as electrons, in the first HEMT barrier layer into the HEMT channel layer
Implementation Method 3
when the gate region depletes the available carriers from the HEMT channel layer, the HEMT channel layer is starved of carriers, thereby selecting the OFF state of the normally OFF HEMT
Data Source
AI summary
A predisposed high electron mobility transistor (HEMT) is disclosed. The predisposed HEMT includes a buffer layer, a HEMT channel layer on the buffer layer, a first HEMT barrier layer over the HEMT channel layer, and a HEMT cap layer on the first HEMT barrier layer. The HEMT cap layer has a drain region, a source region, and a gate region. Further, the HEMT cap layer has a continuous surface on the drain region, the source region, and the gate region. When no external voltage is applied between the source region and the gate region, the gate region either depletes carriers from the HEMT channel layer or provides carriers to the HEMT channel layer, thereby selecting a predisposed state of the predisposed HEMT.