Lateral Bipolar Transistor with Interdigitated Contacts for GaAs Integration
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Solution Overview
Problem
Current bipolar transistor technologies in GaAs HEMT and BiFET technologies face challenges in efficiently integrating pnp transistors with high mobility and low resistance, particularly in forming effective contacts and adapting crystal lattices for enhanced performance.
Innovation Solution
A bipolar transistor design featuring a semiconductor substrate with a high-mobility layer and a donor layer, where the emitter and collector terminals are interdigitated or partially surround each other, and the base terminal forms an ohmic or Schottky contact with a doped base contact region, allowing for integration with HEMT technology and enabling efficient carrier transport.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a lateral pnp transistor is implemented on GaAs substrate, then integration with HEMT technology is achieved, but forming effective ohmic contacts becomes difficult due to material properties
Solution Approach 1:
The patent changes the doping concentration parameter of the semiconductor layer to achieve ohmic contacts. Specifically, the emitter and collector contacts are formed on highly doped n-type semiconductor regions with doping concentrations of 10^18 to 10^20 atoms/cm³, which transforms the contact characteristics from Schottky barrier to ohmic contact, enabling effective current flow in the lateral pnp transistor structure on GaAs substrate.
2Speed
If pseudomorphic HEMT structure is used, then electron mobility is enhanced through quantum well formation, but crystal lattice mismatch becomes an issue
Solution Approach 1:
The patent employs composite materials by combining GaAs substrate with AlGaAs barrier layers forming a heterostructure. The AlGaAs layer has a wider bandgap and different lattice constant than GaAs, creating a pseudomorphic heterostructure that forms quantum wells for high electron mobility while the graded composition (varying Al content) accommodates lattice mismatch through gradual transition, preventing dislocation formation.
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 design achieves improved current gain and low series resistance, enabling efficient integration of pnp transistors with HEMTs in GaAs technology, while allowing for flexible contact configurations and lattice adaptation, thus enhancing transistor performance.
Implementation Method 1
Electrons supplied by the donor layer diffuse into the quantum well
Implementation Method 2
a quantum well is formed in the undoped semiconductor material in the vicinity of the donor layer. Electrons supplied by the donor layer diffuse into the quantum well. The electrons cannot escape from the quantum well and form a two-dimensional electron gas
Implementation Method 3
Because of the heterojunction between the semiconductor materials of different energy band gaps, a quantum well is formed in the undoped semiconductor material in the vicinity of the donor layer
Implementation Method 4
a base contact region of semiconductor material is arranged between the high-mobility layer and the base terminal. The base contact region is doped so that the base terminal forms an ohmic contact on the base contact region
Implementation Method 5
the emitter contact and/or the collector contact is a Schottky contact
Data Source
AI summary
A bipolar transistor includes a substrate of semiconductor material, a high-mobility layer in the substrate, and a donor layer adjacent to the high-mobility layer. An emitter terminal forms an emitter contact on the donor layer, and a collector terminal forms a collector contact on the donor layer. A base terminal is electrically conductively connected with the high-mobility layer. The transistor can be produced in a HEMT technology or BiFET technology in GaAs.