Epitaxial Substrate Buffer Design for Leakage Current and Withstand Voltage
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing epitaxial substrates for HEMT devices face challenges in reducing lateral leakage current while maintaining good lateral and vertical withstand voltage, particularly when operated at high frequencies, due to issues like substrate contamination and inadequate buffer layer design.
Innovation Solution
A Si single crystal substrate with a buffer layer and a main laminated body of epitaxially grown group III nitride layers, featuring an AlN initially grown layer and a superlattice laminate with specific carbon concentrations, is used to enhance both lateral and vertical withstand voltage, and reduce lateral leakage current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a GaN-based low temperature buffer layer is employed on Si substrate, then lateral leakage current is reduced, but through-defects such as pits are generated due to reaction between Si and Ga, deteriorating vertical withstand voltage
Solution Approach 1:
An AlN layer is introduced as an intermediary between the Si substrate and the GaN buffer layer. This AlN layer prevents direct contact and reaction between Si and Ga, eliminating the formation of through-defects and pits, while still allowing the GaN buffer layer to effectively reduce lateral leakage current.
Solution Approach 2:
The buffer layer structure is segmented into multiple functional layers: AlN layer (preventive function), GaN buffer layer (leakage current reduction function), and carbon-containing layers (withstand voltage enhancement function). Each layer performs a specific function to collectively solve the contradiction.
2Object-generated harmful factors
If carbon concentration is increased in the buffer layer to reduce lateral leakage current, then lateral withstand voltage is enhanced, but vertical withstand voltage deteriorates due to insufficient consideration of vertical direction properties
Solution Approach 1:
Carbon is selectively added to specific layers (GaN buffer layer and channel layer) rather than uniformly distributed. The carbon concentration is locally optimized in each layer to simultaneously achieve lateral leakage current reduction and maintain vertical withstand voltage properties.
Solution Approach 2:
The carbon concentration is precisely controlled within specific ranges (1×10^18 to 1×10^20 atoms/cm³ in buffer layer, 1×10^18 to 1×10^21 atoms/cm³ in channel layer) to optimize both lateral and vertical electrical properties without causing detrimental effects.
3Ease of manufacture
If Si substrate is used to reduce cost, then manufacturing cost decreases, but substrate contamination by impurities occurs, increasing loss at high frequencies
Solution Approach 1:
An AlN layer is formed on the Si substrate surface before depositing the GaN buffer layer. This preliminary AlN layer acts as a barrier that prevents Si impurities from contaminating the GaN layers during growth, thereby reducing high-frequency losses while maintaining cost-effectiveness of Si substrate.
Solution Approach 2:
The AlN layer serves as an intermediary barrier between the Si substrate and GaN epitaxial layers, preventing impurity diffusion and contamination, thus enabling high-frequency operation with minimal energy loss while using inexpensive Si substrates.
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 proposed structure effectively decreases lateral leakage current, enhances withstand voltage in both directions, and minimizes losses when the device is operated at high frequencies by optimizing the substrate's resistivity and impurity concentrations.
Implementation Method 1
a superlattice laminate formed by alternate lamination of a first layer made of a Ba1Alb1Gac1Ind1N material and a second layer made of a Ba2Alb2Gac2Ind2N material having a band gap different from that of the first layer
Implementation Method 2
both of the superlattice laminate and a portion, on the buffer side, of the main laminated body has carbon concentration of 1×10^18 to 1×10^20[atoms/cm³]
Implementation Method 3
a main laminated body formed by plural group III nitride layers epitaxially grown on the buffer
Data Source
Figure 1~2
Figure 3(a)~3(c)
Figure 4(a)~4(c)
AI summary
An object of the present invention is to provide an epitaxial substrate for an electronic device capable of making decrease in lateral leakage current and achievement of good properties of withstand voltage in a lateral direction compatible and enhancing withstand voltage in the vertical direction, as well as a method of producing said epitaxial substrate. Specifically, the present invention provides an epitaxial substrate for an electronic device having a Si single crystal substrate, a buffer as an insulating layer formed on the Si single crystal substrate, and a main laminated body formed by plural group III nitride layers epitaxially grown on the buffer, wherein a lateral direction of the epitaxial substrate is defined as an electric current conducting direction, characterized in that: the buffer includes at least an initially grown layer in contact with the Si single crystal substrate and a superlattice laminate constituted of a superlattice multilayer structure on the initially grown layer; the initially grown layer is made of an AlN material; the superlattice laminate is formed by alternate lamination of a first layer made of a Ba1Alb1Gac1Ind1 N (0 ≤ a1 ≤ 1, 0 ≤ b1 ≤ 1, 0 ≤ c1 ≤ 1, 0 ≤ d1 ≤ 1, a1 + b1 + c1 + d1 = 1) material and a second layer made of a Ba2Alb2Gac2Ind2N (0 ≤ a2 ≤ 1, 0 ≤ b2 ≤ 1, 0 ≤ c2 ≤ 1, 0 ≤ d2 ≤ 1, a2 + b2 + c2 + d2 = 1) material having a band gap different from that of the first layer; and both of the superlattice laminate and a portion, on the buffer side, of the main laminated body has carbon concentration of 1 × 1018/cm3 or higher.