GaN HEMT Hole Extraction via Localized Rear Electrode
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Solution Overview
Problem
In AlGaN/GaN high electron mobility transistors (HEMTs), the accumulation of holes generated by impact ionization in the electron transit layer leads to reduced withstand voltage and the Kink effect, which is difficult to address due to the challenge of effectively extracting holes from the layer without degrading high-frequency performance and increasing capacitance.
Innovation Solution
A compound semiconductor device is designed with a substrate having an opening from the rear side, a compound semiconductor layer with a local p-type region exposed at the end of the opening, and a rear electrode connected to the p-type region, allowing for effective extraction of holes generated by impact ionization without increasing capacitance or chip area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a hole extraction electrode is provided on the rear surface of the p-type GaN layer, then holes can be extracted from the electron transit layer, but the entire rear surface is covered with conductive layer which generates capacitance and degrades high-frequency performance
Solution Approach 1:
The patent applies local quality by forming a p-type region only in the peripheral area of the electron transit layer rather than uniformly across the entire layer. This localized p-type doping creates a specific region for hole extraction while leaving the central area intact, thereby extracting holes effectively without covering the entire rear surface with conductive material, thus avoiding excessive capacitance generation and maintaining high-frequency performance.
2Reliability
If a hole extraction electrode is provided on the rear surface, then holes can be extracted, but a high electric field is applied between the drain electrode and the hole extraction electrode which reduces withstand voltage
Solution Approach 1:
The patent localizes the hole extraction function to the peripheral region through selective p-type doping, separating the hole extraction path from the main current path between drain and source. This spatial separation allows hole extraction without creating a high electric field across the entire device structure, thereby maintaining withstand voltage while still effectively removing accumulated holes.
3Reliability
If the electron transit layer is made thinner to facilitate hole extraction, then holes can be removed more easily, but the piezoelectric polarization effect is reduced which decreases 2DEG concentration
Solution Approach 1:
The patent maintains the optimal thickness of the electron transit layer for generating strong piezoelectric polarization and high 2DEG concentration in the central region, while locally modifying only the peripheral area with p-type doping. This approach preserves the polarization effect and electron gas concentration where needed while facilitating hole extraction in the doped peripheral region, avoiding the trade-off between thickness and polarization.
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 solution enables reliable extraction and discharge of holes, maintaining high withstand voltage and high-frequency performance while preventing capacitance-induced breakdowns, thus enhancing the reliability and efficiency of the AlGaN/GaN HEMTs.
Implementation Method 1
holes generated by impact ionization in a high-electric field
Implementation Method 2
distortion occurs in the AlGaN layer due to the difference in lattice constant between GaN and AlGaN. This causes piezoelectric polarization
Implementation Method 3
a high-concentration two-dimensional electron gas (2DEG) is produced by the piezoelectric polarization and AlGaN spontaneous polarization
Data Source
AI summary
A compound semiconductor device includes a substrate having an opening formed from the rear side thereof; a compound semiconductor layer disposed over the surface of the substrate; a local p-type region in the compound semiconductor layer, partially exposed at the end of the substrate opening; and a rear electrode made of a conductive material, disposed in the substrate opening so as to be connected to the local p-type region.