Diamond Semiconductor Device with Mixed Electrode Contacts
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Solution Overview
Problem
Diamond semiconductors have a deep energy level for conductive impurities, resulting in low carrier density and high resistance, making it difficult to achieve high current density through pn junction elements, which is lower than other semiconductor materials like silicon carbide by two orders of magnitude.
Innovation Solution
A semiconductor device structure with a first semiconductor layer of one conductivity type and a second semiconductor layer of a different conductivity type with higher impurity concentration, where one electrode is in ohmic contact and the other in Schottky contact, allowing for a higher impurity concentration and lower resistance, enabling higher current density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If diamond semiconductor is used with conventional pn junction structure, then material properties (wide bandgap, high breakdown voltage) are achieved, but current density is extremely low due to high resistance
Solution Approach 1:
The patent applies local quality by creating a multi-layer structure where different regions have different impurity concentrations. Specifically, it uses a low-impurity diamond layer adjacent to the pn junction for high breakdown voltage, while using high-impurity diamond layers for electrodes to reduce contact resistance and enable high current density. This spatial variation in impurity concentration resolves the contradiction between reliability and productivity.
Solution Approach 2:
The patent employs composite materials by combining diamond layers with different impurity concentrations (low-impurity and high-impurity regions) within a single device structure. The high-impurity diamond regions serve as electrode contact layers with low resistance, while the low-impurity region maintains the intrinsic high breakdown voltage properties of diamond, creating a composite structure that achieves both high reliability and high current density.
2Productivity
If high impurity concentration is used in diamond semiconductor, then resistance decreases and current density increases, but the deep energy level of impurities prevents effective carrier generation
Solution Approach 1:
The patent segments the diamond semiconductor structure into distinct functional regions: high-impurity diamond layers for electrode contact (providing low resistance and high current density) and low-impurity diamond layer for the pn junction region (maintaining high breakdown voltage). This segmentation allows each region to be optimized for its specific function without compromise.
Solution Approach 2:
The patent implements local quality by varying impurity concentration in different spatial regions of the diamond device. The high-impurity regions localized at electrode interfaces provide low contact resistance, while the low-impurity bulk region maintains the high breakdown voltage characteristics, resolving the contradiction between carrier density and breakdown voltage.
3Reliability
If conventional pn junction diode structure is used in diamond, then rectifying function is achieved, but switching speed is limited due to high resistance and low carrier density
Solution Approach 1:
The patent changes the impurity concentration parameter in different regions of the diamond structure. By introducing high-impurity diamond layers at the electrode interfaces, it reduces contact resistance and enables faster carrier injection and extraction, thereby improving switching speed while maintaining the rectifying function in the low-impurity pn junction region.
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 device achieves a significantly higher current density compared to conventional diamond pn diodes, with current densities up to 1000 times higher, and reduces switching loss by allowing fast transition between conductive and non-conductive states.
Implementation Method 1
a first electrode is formed to be in rectifying contact with the first semiconductor layer
Implementation Method 2
a second electrode is formed to be in ohmic contact with the second semiconductor layer
Data Source
AI summary
In this junction element 1, when a forward voltage is applied, a depletion layer is formed in a semiconductor layer 2, prohibiting electrons present in an electrode layer 4 to move into the semiconductor layer 2. For this reason, a majority of holes in a semiconductor layer 3 do not disappear by recombination with conduction electrons in the semiconductor layer 2, but reach the electrode layer 4 while diffusing into the semiconductor layer 2. Accordingly, the junction element 1 can serve as a good conductor for holes, while avoiding the influence of a resistance value, and allows a current to flow therethrough at a level equal to or more than that achieved by a semiconductor element formed of a Si or SiC semiconductor. The present invention is applicable to any semiconductor material in which at least one of a donor level and an acceptor level is located at a sufficiently deep position beyond a thermal excitation energy at an operating temperature, such as diamond, zinc oxide (ZnO), aluminum nitride (AlN), or boron nitride (BN). The present invention is also applicable to even a material having a shallow impurity level at room temperature, such as silicon (Si), silicon carbide (SiC), gallium nitride (GaN), gallium arsenide (GaAs), or germanium (Ge), as long as operation is performed at such a low temperature that the thermal excitation energy can be sufficiently small.