Back-Gated Quantum Well Heterostructure for Vertical Field Control
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Solution Overview
Problem
Existing semiconductor heterostructure designs for quantum computation are limited by a restricted vertical electric field range, which impairs performance due to poor valley splitting and other quantum dot properties, as they cannot exceed the threshold for surface accumulation under the supply gate, typically limiting the vertical field to less than 1 mV/nm to 2 mV/nm.
Innovation Solution
A semiconductor device design incorporating a back gate with a forward-biased 'halo' p-n junction to prevent leakage and allow independent control of vertical electric fields, utilizing a dielectric layer with conductive elements like dot gates, ohmic contacts, and a halo contact to tune electron wave functions over a wider range, enabling vertical fields of 5 mV/nm to 10 mV/nm.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional heterostructure design is used, then the device structure is simple, but the vertical electric field is limited to less than 1 mV/nm to 2 mV/nm due to surface accumulation under the supply gate
Solution Approach 1:
The device is segmented into distinct doped regions: a first doped region extending through the device quantum well layer, a second doped region in the buffer layer, and a third doped region extending from the top layer to the second doped region. This segmentation allows independent control of vertical electric fields in different spatial zones, enabling the quantum well region to achieve high vertical fields (5-10 mV/nm) while the supply gate region maintains lower fields to prevent surface accumulation.
Solution Approach 2:
Different doped regions are assigned different conductivity types and doping concentrations tailored to their specific functions. The first doped region (n-type) provides electron supply, the second doped region (p-type) creates a pn junction barrier, and the third doped region (p-type) forms the halo structure. This local differentiation of electrical properties enables simultaneous optimization of quantum dot performance and supply gate stability.
2Reliability
If a forward-biased halo p-n junction is added to prevent leakage, then leakage is reduced and vertical field control is improved, but the device complexity increases
Solution Approach 1:
The halo p-n junction structure acts as an intermediary barrier between the supply gate region and the quantum well region. The second doped region (p-type) and third doped region (p-type) create a pn junction that provides a potential barrier to prevent carrier leakage while allowing the vertical electric field to be independently controlled in the quantum well region, thus mediating between the conflicting requirements of leakage prevention and field control.
Solution Approach 2:
The doping concentration in the second doped region is set to be sufficiently great to avoid freeze-out of carriers at temperatures less than 5 K (at least 10^18/cm³), while the first doped region has a peak dopant concentration of at least 10^19/cm³. These parameter changes ensure reliable leakage prevention through the pn junction while maintaining the desired electrical properties for quantum dot operation.
3Adaptability or versatility
If the vertical electric field is increased to 5 mV/nm to 10 mV/nm, then valley splitting and quantum dot properties are improved, but surface accumulation under the supply gate occurs
Solution Approach 1:
The vertical electric field control is segmented into independent zones: the quantum well region can sustain high vertical fields (5-10 mV/nm) for improved valley splitting, while the supply gate region is protected by the halo p-n junction structure that prevents surface accumulation. This spatial segmentation allows each region to operate at its optimal field strength without adversely affecting the other.
Solution Approach 2:
The halo p-n junction structure is designed in advance to counteract the harmful effect of surface accumulation before it can occur. The second and third doped regions create a potential barrier that preemptively prevents carrier accumulation at the supply gate interface, allowing high vertical fields to be applied to the quantum well without triggering the harmful accumulation effect.
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 design enhances the dynamic range of achievable vertical electric fields, improving valley splitting and other quantum dot properties by preventing leakage and allowing independent control of the vertical electric field, thereby increasing the performance of semiconductor devices.
Implementation Method 1
A forward-biased 'halo' p-n junction is utilized to prevent leakage and unwanted accumulation in the ohmic and supply gate regions
Implementation Method 2
A semiconductor device design is described that enables back gating of heterostructures with a larger dynamic range of allowable electric fields
Implementation Method 3
a dielectric layer with conductive elements like dot gates, ohmic contacts, and a halo contact to tune electron wave functions
Data Source
AI summary
A semiconductor device. In some embodiments, the semiconductor device includes a back gate layer; a buffer layer, on the back gate layer; a device quantum well layer, on the buffer layer; a cap layer, on the device quantum well layer; a top layer, on the cap layer; a first doped region of a first conductivity type, extending at least part-way through the device quantum well layer; a second doped region, of a second conductivity type, within the buffer layer; and a third doped region, of the second conductivity type extending from the top layer to the second doped region. The top layer may include a dielectric layer, and, in the dielectric layer, a plurality of conductive elements, including one or more dot gates, an ohmic contact, a bath gate, a supply gate, and a halo contact.