GaN HBT Structure for Low-Resistance Base Contact
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Solution Overview
Problem
In GaN-based HBT structures with N polarity as the principal plane orientation, achieving good ohmic contact between the base layer and the base electrode is challenging due to the high resistance of the emitter layer, which is necessary for generating a two-dimensional hole gas, and complete removal of the emitter layer leads to a reduction in the two-dimensional hole gas concentration.
Innovation Solution
A bipolar transistor structure with a sub-collector layer of n-type nitride semiconductor, a collector layer of InGaN, a base layer of GaN, and an emitter layer of Al-containing nitride semiconductor, where the principal surfaces are Group V polar planes, facilitating the formation of a two-dimensional hole gas and improving ohmic contact between the base layer and the base electrode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the emitter layer is kept to generate two-dimensional hole gas, then the hole gas concentration is maintained, but the ohmic contact resistance between base layer and base electrode increases due to high resistance of the emitter layer
Solution Approach 1:
The emitter layer is divided into two functional regions: a first emitter layer region that contacts the base electrode to provide low resistance ohmic contact, and a second emitter layer region that generates and maintains the two-dimensional hole gas. This segmentation allows each region to optimize its function independently, resolving the contradiction between maintaining hole gas concentration and reducing contact resistance.
Solution Approach 2:
Different portions of the emitter layer are given different properties: the first emitter layer region has properties optimized for electrical contact (lower resistance), while the second emitter layer region has properties optimized for hole gas generation (higher Al content, specific thickness). This local differentiation of properties allows the structure to simultaneously achieve low contact resistance and high hole gas concentration.
2Object-affected harmful factors
If the emitter layer is partially or completely removed to reduce contact resistance, then the ohmic contact improves, but the two-dimensional hole gas concentration is reduced
Solution Approach 1:
The emitter layer is segmented into two distinct regions with different functions. The first region serves as the contact region with reduced thickness or modified properties for low resistance, while the second region maintains the optimal structure for hole gas generation. This segmentation resolves the contradiction by allowing removal or modification of only the contact portion while preserving the hole gas generation portion.
Solution Approach 2:
The first emitter layer region acts as an intermediary between the base electrode and the second emitter layer region. It provides a low-resistance electrical pathway while the second region continues to generate the two-dimensional hole gas. This intermediary structure allows the system to achieve both low contact resistance and high hole gas concentration simultaneously.
3Quantity of substance
If p-type doping is attempted in GaN to increase hole concentration, then the hole concentration should increase, but the dopant is inactivated by hydrogen and the hole concentration cannot be increased
Solution Approach 1:
The patent replaces the chemical doping mechanism (which fails due to hydrogen inactivation) with a physical mechanism based on polarization effects. By using AlGaN/GaN heterostructures with specific compositions and the piezoelectric effect, the system generates two-dimensional hole gas without relying on p-type dopants, thereby avoiding the hydrogen inactivation problem entirely.
Solution Approach 2:
The invention changes the fundamental parameter for achieving high hole concentration from dopant concentration to polarization-induced carrier accumulation. By controlling the Al content, layer thickness, and structural configuration of the AlGaN/GaN heterostructure, the system achieves high hole concentration through polarization effects rather than chemical doping, bypassing the dopant inactivation issue.
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 configuration allows for good ohmic contact between the base layer and the base electrode, maintaining high two-dimensional hole gas concentration and reducing base contact resistance, even if the emitter layer is partially or completely removed, thereby enhancing the high-frequency characteristics of the HBT.
Implementation Method 1
the nitride semiconductor is a material having polarization in a c-axis direction, and generally crystal growth is carried out in the (+c-axis direction) plane orientation called a Group III polar plane to manufacture a device. In the case of a Group III polar plane, when AlGaN is grown on GaN, the band is bent by an electric field due to a difference in magnitude of spontaneous polarization between materials and a polarization electric field generated by distortion generated in an AlGaN layer, and a two-dimensional electron gas is generated at an interface between AlGaN and GaN.
Implementation Method 2
the band is bent by an electric field due to a difference in magnitude of spontaneous polarization between materials and a polarization electric field generated by distortion generated in an AlGaN layer
Implementation Method 3
A bipolar transistor structure with a sub-collector layer of n-type nitride semiconductor, a collector layer of InGaN, a base layer of GaN, and an emitter layer of Al-containing nitride semiconductor, where the principal surfaces are Group V polar planes, facilitating the formation of a two-dimensional hole gas and improving ohmic contact between the base layer and the base electrode.
Data Source
AI summary
A hetero-junction bipolar transistor includes an n-type collector layer made of InGaN, a base layer formed on the collector layer and made of GaN, and an emitter layer formed on the base layer and made of a nitride semiconductor containing Al, in which the collector layer, the base layer, and the emitter layer are formed in a state in which the principal surface is a group V polar plane. The base electrode can be formed in contact with the upper part of the base layer around the emitter layer formed in a mesa shape.