Preparation and ultraviolet detection performance of Cu doped <i>β</i>-Ga<sub>2</sub>O<sub>3</sub> thin films
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2023-01-01 |
| Journal | Acta Physica Sinica |
| Authors | Wei Liu, Qiu-Ju Feng, Ziqi Yi, Yu Chen, Shuo Wang |
| Citations | 2 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Cu-Doped $\beta$-Ga2O3 Thin Films for Solar-Blind UV Detection
Section titled “Technical Documentation & Analysis: Cu-Doped $\beta$-Ga2O3 Thin Films for Solar-Blind UV Detection”Executive Summary
Section titled “Executive Summary”This research successfully demonstrates the fabrication and characterization of p-type Cu-doped $\beta$-Ga2O3$ thin films grown on sapphire via Chemical Vapor Deposition (CVD) for high-performance Solar-Blind UV Photodetectors (SBPs).
- P-Type Achievement: Successful realization of p-type conductivity in $\beta$-Ga2O3$ through Cu doping, achieving hole concentrations up to $1.69 \times 10^{16}$ cm-3.
- High Sensitivity: The optimized device (2.4% Cu content) exhibited a high photo-to-dark current ratio (Ip/Id) of $3.81 \times 10^{2}$ under 254 nm illumination at 10 V bias.
- Rapid Response: The photodetector demonstrated fast switching speeds, with rise and decay times measured at 0.11 s and 0.13 s, respectively.
- Efficiency Metrics: Peak responsivity ($R$) reached 1.72 A/W, and External Quantum Efficiency (EQE) reached 841% at a low light intensity of 64 µW/cm2.
- Structural Confirmation: X-ray Diffraction (XRD) confirmed that Cu2+ successfully substitutes Ga3+ within the $\beta$-Ga2O3$ lattice, causing a shift in the (201) diffraction peak toward lower angles.
- Device Structure: A Metal-Semiconductor-Metal (MSM) structure was fabricated using thermally evaporated Au interdigitated electrodes.
Technical Specifications
Section titled “Technical Specifications”The following table summarizes the key performance metrics extracted from the optimized Cu-doped $\beta$-Ga2O3$ photodetector (Device C).
| Parameter | Value | Unit | Context | | :--- | :--- | :--- | :--- | | Target Wavelength | 254 | nm | Solar-Blind UV Illumination | | Operating Bias | 10 | V | Applied Voltage | | Max Photo-to-Dark Ratio (Ip/Id) | $3.81 \times 10^{2}$ | Ratio | Device C (2.4% Cu content) | | Peak Responsivity ($R$) | 1.72 | A/W | At 64 µW/cm2 light intensity | | External Quantum Efficiency (EQE) | 841 | % | At 64 µW/cm2 light intensity | | Rise Time ($\tau_{r}$) | 0.11 | s | Response Speed | | Decay Time ($\tau_{d}$) | 0.13 | s | Recovery Speed | | Hole Concentration ($p$) | $1.69 \times 10^{16}$ | cm-3 | Device C (Hall Measurement) | | Hall Mobility ($\mu$) | 4.52 | cm2/(V·s) | Device C | | Optical Bandgap ($E_{g}$) | 4.80 | eV | Device C (Tauc Plot) | | Electrode Material | Au | N/A | Electron Beam Evaporation | | Electrode Dimensions | 20 / 20 | µm | Width / Spacing of Interdigitated Electrodes |
Key Methodologies
Section titled “Key Methodologies”The Cu-doped $\beta$-Ga2O3$ thin films were synthesized using a cost-effective Chemical Vapor Deposition (CVD) method on sapphire substrates.
- Substrate Preparation: Sapphire (Al2O3) substrates were cleaned via ultrasonic agitation using acetone, ethanol, and deionized water.
- Precursor Formulation: High-purity Ga2O3 powder (99.99%), CuO powder (99.99%), and Carbon powder (99.99%, acting as a reducing agent) were uniformly mixed and ground.
- CVD Setup: The mixed powder was placed in an alumina boat, and the polished sapphire substrate was positioned directly above the source material.
- Growth Parameters (Optimized Sample C):
- Growth Temperature: 1000 °C
- Reaction Time: 30 min
- Precursor Ratio (Ga2O3/CuO): 25:3 (by mass)
- Gas Flow Rates:
- Carrier Gas (Ar): 200 mL·min-1
- Reaction Gas (O2): 50 mL·min-1
- Device Fabrication: Au interdigitated electrodes were deposited onto the resulting thin film using electron beam evaporation to create the Metal-Semiconductor-Metal (MSM) photodetector structure.
6CCVD Solutions & Capabilities
Section titled “6CCVD Solutions & Capabilities”While this research focuses on $\beta$-Ga2O3$, the application—high-performance Solar-Blind UV detection—is a core strength of diamond technology. Diamond, with its ultra-wide bandgap (5.5 eV) and superior material properties, offers significant advantages over Ga2O3 (4.9 eV) for next-generation SBPs, especially those requiring extreme speed, high temperature operation, or radiation hardness.
6CCVD provides the foundational MPCVD materials necessary to replicate or significantly exceed the performance demonstrated in this study.
Applicable Materials for Advanced UV Detection
Section titled “Applicable Materials for Advanced UV Detection”| 6CCVD Material | Application Relevance | Key Advantage over $\beta$-Ga2O3$ | | :--- | :--- | :--- | | Optical Grade SCD | High-sensitivity, low-noise SBPs, UV optics, and windows. | Higher Bandgap (5.5 eV): Provides superior intrinsic solar-blindness and lower dark current. | | Boron-Doped Diamond (BDD) | P-type wide-bandgap semiconductors, high-speed detectors, and high-power electronics. | Superior P-Type Performance: BDD offers vastly higher hole mobility and thermal conductivity (2000 W/m·K vs. Ga2O3’s ~10 W/m·K), crucial for high-flux detection and thermal management. | | Polycrystalline Diamond (PCD) | Large-area UV detectors, thermal spreaders, and robust sensor platforms. | Large Area Capability: 6CCVD offers PCD plates up to 125mm, enabling scalable device manufacturing far beyond typical SCD or Ga2O3 limits. |
Customization Potential for Device Replication and Extension
Section titled “Customization Potential for Device Replication and Extension”The fabrication of high-performance photodetectors requires precise material engineering and integration, capabilities where 6CCVD excels:
- Custom Dimensions and Substrates: While the paper used sapphire, 6CCVD can supply SCD and PCD plates/wafers up to 125mm in diameter, suitable for large-scale device arrays or integration onto complex systems. We offer custom laser cutting for unique shapes and dimensions.
- Precision Polishing: The performance of thin-film devices is highly dependent on surface quality. 6CCVD guarantees ultra-smooth surfaces:
- SCD: Ra < 1nm
- PCD (Inch-size): Ra < 5nm
- Integrated Metalization Services: The research utilized Au electrodes. 6CCVD offers comprehensive in-house metalization capabilities, including:
- Standard Contacts: Au, Pt, Pd, Ti, W, Cu.
- Custom Stacks: We can deposit multi-layer stacks (e.g., Ti/Pt/Au) optimized for ohmic contact formation on wide-bandgap materials like BDD, ensuring low contact resistance critical for high-speed MSM devices.
Engineering Support
Section titled “Engineering Support”The successful p-type doping of $\beta$-Ga2O3 is a significant material science challenge. Similarly, achieving optimal doping and crystal quality in diamond requires specialized expertise.
- Doping Optimization: 6CCVD’s in-house PhD team specializes in controlling doping profiles (Boron, Nitrogen) in MPCVD diamond. We can assist researchers transitioning from Ga2O3 to BDD for Solar-Blind UV Photodetector projects, ensuring optimal carrier concentration and mobility for superior device performance.
- Thermal Management: Diamond’s unparalleled thermal conductivity is essential for high-power or high-flux UV applications where Ga2O3’s poor thermal properties lead to self-heating effects (as noted in the paper, causing responsivity degradation). 6CCVD materials provide the necessary thermal platform.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Solar-blind UV photodetectors (SBPs) have attracted great attention because they are widely used in missile tracking, fire detection, biochemical analysis, astronomical observations, space-to-space communications, etc. At present, it is found that wide bandgap semiconductor materials such as Al<sub><i>x</i></sub>Ga<sub>1-<i>x</i></sub>N, Mg<sub>1</sub>Zn<sub>1-<i>x</i></sub>O, diamond and <i>β</i>-Ga<sub>2</sub>O<sub>3</sub> are ideal semiconductor materials for developing high-performance SBPs. The ultra-wide band gap semiconductor material, <i>β</i>-Ga<sub>2</sub>O<sub>3</sub>, has a large band gap width of 4.9 eV, strong breakdown electric field, absorption edge located in the solar blind ultraviolet band (200-280 nm), and it also has high transmittance in the near ultraviolet and the whole visible band. Therefore, <i>β</i>-Ga<sub>2</sub>O<sub>3</sub> is a very suitable material for making solar blind UV photodetectors. However, the p-type <i>β</i>-Ga<sub>2</sub>O<sub>3</sub> is difficult to dope, which limits the further development of <i>β</i>-Ga<sub>2</sub>O<sub>3</sub> devices. In this work, the <i>β</i>-Ga<sub>2</sub>O<sub>3</sub> thin films with different Cu doping content are grown on sapphire substrates by chemical vapor deposition method, and the morphology, crystal structure and optical properties of <i>β</i>-Ga<sub>2</sub>O<sub>3</sub> films are measured. The test results show that the surfaces of <i>β</i>-Ga<sub>2</sub>O<sub>3</sub> films with different Cu content are relatively smooth, and the (<inline-formula><tex-math id=“M2”>\begin{document}$ \bar 201 $\end{document}</tex-math><alternatives><graphic xmlns:xlink=“http://www.w3.org/1999/xlink” xlink:href=“19-20230971_M2.jpg”/><graphic xmlns:xlink=“http://www.w3.org/1999/xlink” xlink:href=“19-20230971_M2.png”/></alternatives></inline-formula>) diffraction peak positions shift toward the lower degree side with the increase of Cu content, which indicates that Cu<sup>2+</sup> replaces Ga<sup>3+</sup> and enters into the <i>β</i>-Ga<sub>2</sub>O<sub>3</sub> lattice. The optical absorption spectrum measurement indicates that the energy gaps of samples are evidently narrowed with the increase of Cu doping concentration. Hall measurements indicate that the Cu doped <i>β</i>-Ga<sub>2</sub>O<sub>3</sub> thin films have a p-type conductivity with a hole concentration of 7.36 × 10<sup>14</sup>, 4.83 × 10<sup>15</sup> and 1.69 × 10<sup>16 </sup>cm<sup>-3</sup>, respectively. In addition, a photoconductive UV detector with metal-semiconductor-metal structure is prepared by evaporating Au on a Cu-doped <i>β</i>-Ga<sub>2</sub>O<sub>3</sub> thin film, and its UV detection performance is studied. The results show that the photocurrent value of the device increases with Cu content increasing. The photo-to-dark current ratio (<i>I</i><sub>l</sub>/<i>I</i><sub>d</sub>) is about 3.8×10<sup>2</sup> of 2.4% Cu content device under 254 nm-wavelength light at 10 V. The rise time and decay time are 0.11 s and 0.13 s, respectively. Furthermore, the responsivity and external quantum efficiency can reach 1.72 A/W and 841% under 254 nm-wavelength light with a light intensity of 64 μW/cm<sup>2</sup>.