AlGaAs-CMOS Technology

• AlGaAs-CMOS technology is the integration of AlGaAs compound semiconductor heterostructures with standard CMOS processes, enabling high tunability and robust performance.
• Advanced gate architectures and precise epitaxial growth allow for controlled quantum well formation and quantized conduction, essential for spin-based quantum and photonic applications.
• Innovative device designs, such as triple mesa Geiger-mode photodiodes, enhance radiation tolerance and photon detection efficiency for applications in high-energy physics and medical imaging.

AlGaAs-CMOS technology integrates aluminum gallium arsenide (AlGaAs) compound semiconductor heterostructures with complementary metal-oxide-semiconductor (CMOS) processing, targeting tunable, efficient, and radiation-tolerant nanoelectronic and optoelectronic devices. Leveraging high-mobility quantum wells, precise gate engineering, and advanced lithography, this technology supports the fabrication of quantum point contacts, Geiger-mode photodiodes, and lateral p–n junction light-emitting diodes, while ensuring compatibility with standard CMOS integration strategies. AlGaAs-CMOS platforms are foundational for applications that require high tunability, low noise, and robust operation under radiation exposure, and are positioned as key enabling technologies for future spin-based quantum information and photonic systems.

1. Material Engineering and Heterostructure Design

AlGaAs-CMOS architectures utilize epitaxial layers of GaAs and AlAs (or Al$_{x}$Ga$_{1-x}$As alloys) to produce heterostructures with controlled electronic properties. The GaAs layer features a direct bandgap of 1.424 eV, ensuring efficient photon absorption, while the higher-bandgap AlAs layer (≈2.168 eV) serves as an optical window or barrier for carrier confinement within quantum wells. The lattice constants of GaAs (≈5.65 Å) and AlAs (≈5.66 Å) facilitate coherent heterointerface formation, minimizing defect states and interface-induced leakage currents, particularly under radiation stress (Downing et al., 13 Feb 2024).

Carbon doping in p-type GaAs/AlGaAs heterostructures enables shallow two-dimensional hole systems, critical for fabricating spin-coherent nanostructures. The incorporation of quantum wells, formed by modulation doping and precise compositional control, sets the foundation for device elements such as quantum point contacts and lateral p–n junctions with tailored carrier densities and spin-orbit interaction strengths (Csontos et al., 2010, Dobney et al., 15 Aug 2024).

2. Advanced Gate Architectures and Tunability

Device tunability in AlGaAs-CMOS relies on the synergistic use of intrinsic in-plane gates and evaporated metallic top-gates. In-plane gates are patterned by local anodic oxidation lithography using an atomic force microscope (AFM) tip, directly modulating the electronic width and confinement potential of quantum point contacts (QPCs). Evaporated top-gates, typically separated by a high-quality gate insulator (e.g., 20 nm HfO$_{2}$ via atomic layer deposition), independently control the device’s electrochemical potential (Csontos et al., 2010).

These complementary gates afford high versatility in electronic tuning. Device conductance ($G$) is precisely controlled through applied voltages $V_{\rm tg}$ (top-gate) and $V_{\rm G1}, V_{\rm G2}$ (in-plane gates), supporting robust quantized conductance and stable operation. Improved leakage performance is achieved by engineering the insulator oxide properties. This methodology is extensible to the integration of high-density CMOS circuits with quantum nanoelectronic elements.

3. Radiation Tolerance and Compact Photodiode Design

AlGaAs-based Geiger-mode photodiodes provide substantial radiation tolerance via layered bandgap engineering and device miniaturization. Devices with sub-micrometer active thicknesses (<1 μm) exhibit attenuated cross-sections for neutron/gamma interactions, in contrast to silicon photodiodes. For instance, the photon attenuation length at 400 nm in GaAs (≈15 nm) is much lower than in silicon, supporting enhanced robustness in radiation fields (Downing et al., 13 Feb 2024).

The triple mesa structure is a critical design innovation, splitting the device into nested mesa regions (top/middle/bottom) and concentrating the highest electric fields within the device center. This configuration yields peak central fields of ≈4 × 10$^{7}$ V/m—3–6× larger than at corners/surfaces—mitigating peripheral breakdown and leakage:

$$E(y, r) \approx E_{\mathrm{bulk}} \cdot \exp\left[-\alpha(r-r_{\mathrm{center}})^{2}\right]$$

Field modeling demonstrates that breakdown is confined and avalanche gain is maximized, enabling solid-state photomultiplier arrays (SPADs/SSPMs) with quantum efficiencies up to 52% (experimentally) and 61% (simulated) at 500 nm. This establishes AlGaAs-CMOS as preferential for sensor deployments in high-energy physics, medical imaging, and space environments.

4. Fabrication Workflows and CMOS Compatibility

Fabrication of AlGaAs-CMOS structures employs standard semiconductor processing with adaptations for compound material systems. Key steps include:

• Wet chemical etching: Selective removal of donor/acceptor layers to define regions of n-type or p-type conductivity (Dobney et al., 15 Aug 2024).
• Local anodic oxidation lithography (AFM): Precise patterning of nanoelectronic structures, e.g., QPCs (Csontos et al., 2010).
• Electron-beam lithography: Sub-100 nm definition of inducing gates for p–n junctions and single-electron devices.
• Atomic layer deposition (ALD): Deposition of insulators such as HfO$_{2}$ (20 nm) or Al$_{2}$O$_{3}$ (100 nm) for gate isolation.
• Thermal evaporation and alloyed contacts: AuGeNi for n-type; AuBe for p-type ohmic contact formation.

These steps retain full compatibility with conventional CMOS workflows, optimizing the integration of quantum devices and optoelectronic elements without disruption to established lithographic and process protocols (Dobney et al., 15 Aug 2024). This suggests direct path to hybrid quantum-classical integrated circuits.

5. Quantum Devices and Optoelectronic Phenomena

AlGaAs-CMOS platforms support the formation of lateral p–n junctions and light-emitting diodes (LEDs) on n-type high-mobility GaAs/Al$_{0.33}$Ga$_{0.67}$As heterostructures (Dobney et al., 15 Aug 2024). Key processes include donor layer removal and gate-induced hole generation to create two-dimensional electron and hole gases adjacent to each other. Controlled electroluminescence is observed from the GaAs quantum well, with:

• Emission peak centered at ≈812 nm, FWHM ≈8 nm, indicative of neutral exciton recombination.
• Diode current follows Shockley relation:

$I = I_0 \left( e^{\frac{qV}{k_BT}} - 1 \right)$

• Radiative recombination rate proportional to carrier densities:

$R_{\mathrm{rad}} \propto n\,p$

Lithographic definition accuracy (≤100 nm) supports the direct integration of single-electron pumps adjacent to p–n junctions, forming deterministic single-photon sources. This facilitates applications in quantum communications, single-photon imaging, and scalable quantum device arrays.

6. Applications and Functional Impact

AlGaAs-CMOS technology enables key advances in several fields:

Application Area	Key AlGaAs-CMOS Features	Significance
Spin-based Quantum Information	Tunable QPCs via hybrid gating	Long spin relaxation, suppressed hyperfine coupling
Radiation-tolerant Photodetectors	Thin triple-mesa design	Low dark current, longevity in harsh environments
Quantum Light Sources	Lateral p–n junction LEDs, e-pumps	On-demand single-photon emission
Many-body Quantum Phenomena	Strong spin-orbit and Coulomb effects	Studies of reduced-dimensional interactions

Accurate gating and robust material engineering support stable low-power operation, essential for future quantum computation and multi-modal sensing architectures (Csontos et al., 2010, Downing et al., 13 Feb 2024, Dobney et al., 15 Aug 2024).

7. Future Directions and Integration Prospects

AlGaAs-CMOS technologies are positioned for extending classical CMOS capabilities into quantum and photonic domains. Anticipated developments include:

• Larger-scale SPAD arrays for scientific/medical instrumentation leveraging high radiation tolerance and low-noise characteristics.
• Integrated quantum processing chips combining spin-coherent elements with classical control circuitry, enabled by hybrid gate and doping architectures.
• Enhanced optoelectronic device integration, such as single-photon sources and modulators, directly compatible with standard fabrication and packaging protocols.
• Potential improvement in emission peak spectral width by optimizing induced hole densities and quantum well configurations.

A plausible implication is that continued advancement in lithographic precision and oxide engineering will further suppress leakage currents and enhance operational reliability, consolidating AlGaAs-CMOS as a platform for next-generation quantum information and photonics systems.