Nitride Semiconductor HEMT Trap Layer for Short-Channel Effect
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Solution Overview
Problem
High electron mobility transistors (HEMTs) suffer from a short-channel effect and current collapse phenomenon due to the generation of electron traps in the back barrier layer, which reduces their output and amplification capabilities, especially when the gate length is shortened below 120 nm.
Innovation Solution
A compound semiconductor device is designed with an electron transit layer doped with an impurity to form a trap level, preventing holes generated by collision ionization from reaching the deep portion of the layer, thereby suppressing the short-channel effect and current collapse phenomenon by using a specific doping concentration profile and layer structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the gate length is shortened to increase output and frequency, then higher output and frequency are achieved, but the short-channel effect occurs causing threshold voltage decrease and drain leakage current
Solution Approach 1:
The patent applies local quality by creating a non-uniform doping concentration profile within the electron transit layer. The doping concentration is set to be higher in the deep portion (near the back barrier layer) and lower in the upper portion, allowing different regions to serve different functions: the high-doping region suppresses short-channel effects and traps holes, while the low-doping region maintains high electron mobility in the channel region.
Solution Approach 2:
The patent introduces an intermediary mechanism by using a specifically doped region (with impurity forming trap levels) as a mediator between the back barrier layer and the channel. This intermediary region captures holes generated by collision ionization before they can reach the deep portion, thereby suppressing the short-channel effect without requiring a longer gate length.
2Speed
If the gate length is shortened to increase frequency, then higher frequency is achieved, but drain leakage current increases due to short-channel effect
Solution Approach 1:
The patent converts the harmful effect of collision ionization into a beneficial one by intentionally introducing impurities that form trap levels in the deep portion of the electron transit layer. These trap levels capture the holes generated by collision ionization, preventing them from causing drain leakage current. Thus, the harmful hole generation is transformed into a useful hole trapping mechanism that suppresses leakage.
Solution Approach 2:
The doping concentration is locally optimized in the deep portion of the electron transit layer to specifically address the leakage problem near the drain, while maintaining low doping in the upper portion to preserve electron mobility. This localized quality enhancement allows short gate lengths to be used without suffering from increased drain leakage.
3Quantity of substance
If AlGaN layer with different lattice constant is formed to induce two-dimensional electron gas, then polarization is induced and electron gas is generated, but distortion is generated in the AlGaN layer due to lattice constant difference
Solution Approach 1:
The patent changes the physical parameters of the electron transit layer by introducing controlled impurity doping with specific concentrations. This parameter change allows the layer to accommodate the lattice mismatch distortion through controlled trap level formation, while still maintaining the polarization-induced two-dimensional electron gas. The doping concentration is carefully optimized to balance distortion accommodation with electron gas generation.
4Reliability
If doping concentration is increased to suppress short-channel effect, then short-channel effect is suppressed, but electron mobility decreases
Solution Approach 1:
The patent resolves this contradiction by applying local quality with a spatially varying doping concentration profile. The doping concentration is high in the deep portion (near the back barrier) to suppress short-channel effects and trap holes, but low in the upper portion (channel region) to maintain high electron mobility. This localized differentiation allows both requirements to be satisfied simultaneously in different regions.
Solution Approach 2:
The patent transitions from a uniform one-dimensional doping approach to a graded or non-uniform doping profile across the depth of the electron transit layer. By introducing depth-dependent doping concentration, the solution operates in an additional dimensional space (depth profile), allowing simultaneous optimization of short-channel suppression and electron mobility that cannot be achieved with uniform doping.
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 effectively suppresses the short-channel effect and current collapse phenomenon, enhancing the pinch-off characteristic and amplification factor of the HEMT, particularly at gate lengths equal to or shorter than 120 nm, while maintaining electron mobility.
Implementation Method 1
an electron transit layer formed on the substrate and made of nitride semiconductor doped with an impurity that forms a trap level
Implementation Method 2
holes generated by collision ionization
Implementation Method 3
by piezoelectric polarization in the AlGaN layer generated due to this distortion
Implementation Method 4
by spontaneous polarization of the AlGaN itself
Data Source
AI summary
A compound semiconductor device disclosed herein includes: a substrate; an electron transit layer formed on the substrate and made of nitride semiconductor doped with an impurity that forms a trap level; a barrier layer formed on the electron transit layer; and a source electrode, a drain electrode, and a gate electrode formed over the electron transit layer at a distance from one another, wherein the electron transit layer includes: a first conductivity type region; a second conductivity type region located over the first conductivity region, where the second conductivity type region having an electron concentration higher than an electron concentration of the first conductivity type region; and a third conductivity type region located over the second conductivity type region, where the third conductivity type region having an electron concentration lower than a concentration of the impurity and being in contact with an upper surface of the electron transit layer.