Popular Semiconductor Materials: Application Introduction of Gallium Arsenide
Background
Gallium arsenide (GaAs) (Item No.:G119227) is a compound made of two elements, gallium and arsenic, which are important group IIIA and VA semiconductor materials. Therefore, GaAs is also an important compound semiconductor material, GaAs has a bright gray appearance, metallic luster, brittle and hard. It is stable at room temperature and does not react with hydrochloric acid, sulfuric acid and hydrofluoric acid, but can react with concentrated nitric acid and also with hot hydrochloric acid(Item No.:H399545) and sulfuric acid(Item No.:S399850). When it is heated to 873K, the appearance begins to generate oxides and form oxide films. In addition, GaAs also has better electronic properties, such as higher saturation electron rate and electron mobility, faster switching speed, resistance to natural radiation and a series of unique properties.
GaAs is naturally scarce and is usually obtained by direct gallium and arsenic synthesis, of which horizontal zone melting is a common method. Single crystals can be obtained by regional purification. GaAs can also be obtained by indirect methods, such as GaCl(Item No.:G345285) reduction by arsenic vapor(Item No.:A110123) (Eq. 1), or GaAs by thermal decomposition of Ga(CH3) and AsH3 at a certain temperature (Eq. 2).
4GaCl + 2H2 + As4 → 4GaAs + 4HCl (i)
Ga (CH3)3 + AsH3 → GaAs + 3CH4 (ii)
Applications
GaAs has many excellent characteristics and its applications are very broad, which can be broadly divided into four major areas: RF (radio frequency), PHOTONICS (optoelectronics), LED (light emitting diode) and PV (photovoltaic power generation).
RF Devices
The main function of RF devices is to achieve signal transmission and reception, by the power amplifier (Power Amplifier, PA), RF switches, filters, digital-to-analog/analog- to-digital converters and other devices. GaAs is used in the field of RF, the main link is the PA. after the PA amplified signal, and finally emitted from the device, belongs to the communication equipment high energy link.
Recently, Nguyen et al. [1] designed a stacked field-effect transistor PA with a harmonic tuned output matching network using 0.15 μm GaAs. the prepared PA has 28.5 dBm output power, 12 dB gain, and 38.4% power-added efficiency (PAE). This is the first time that stacked field-effect transistor technology is combined with a harmonic tuned output network to achieve high PAE and highly power density in a GaAs PA.
Figure 1: Power amplifier chip photo (1.1 mm × 0.8 mm)[1]
In addition, GaAs also occupies a dominant position in the field of 5G cell
phone PA. GaAs has higher saturation electron rate and electron mobility, which
makes it suitable for application in high frequency scenarios and has lower
noise in high frequency operation; at the same time, because GaAs has higher
breakdown voltage than Si, so GaAs is more suitable for application in high
power situations. Because of these characteristics, GaAs in the 5G era, will
still be the main material for power amplifiers and RF switches and other cell
phone RF devices.
Optical Devices
Another advantage of GaAs is its direct energy gap, which gives it a better
optoelectronic performance and can be used to make optoelectronic devices.
Infrared lasers and sensors made using GaAs substrates have received a lot of
attention because of their highly power density, low energy consumption, high
temperature resistance, high luminescence efficiency, high breakdown voltage
and other characteristics.
Efficient photovoltaic conversion is a relentlessly pursued goal, and is of great importance in promoting the development and application of new energy and information fields. Photonic power converters or photoelectric sensors can absorb the infrared laser power transmitted through a multimode fiber and convert it to electrical power for remote use. To convert this power into a useful voltage, Hinzer et al. [2] designed and fabricated a GaAs photovoltaic photovoltaic sensor that uses a single, lattice-matched, vertically stacked single-cell device to generate >5 V, thereby eliminating complex fabrication and assembly steps. Experimental measurements also show conversion efficiencies of up to 60.1% at a wavelength of 835 nm and a light intensity of 11 W/cm2.
Figure 2: Schematic diagram of the experimental setup [2]
LED devices
Light-emitting diode (LED) is a solid light-emitting device composed of compound semiconductors (GaAs, GaN, etc.), which can convert electrical energy into light energy. LEDs made of different materials emit different wavelengths and colors of light. LEDs can be distinguished into conventional LEDs, Mini LEDs, Micro LEDs and other types according to chip size, among which Mini LEDs and Micro LEDs are used in the new generation of displays.
Electroluminescence (electron to photon conversion in LEDs) can be used as a refrigeration mechanism provided that the LEDs have a high quantum efficiency. Xiao et al. [3] investigated the practical application of electroluminescence in refrigeration by optimizing GaAs/GaInP double hetero-structured LEDs. The study firstly developed a design model based on fine equilibrium physics and statistical ray optics methods, and predicted an external luminescence efficiency 97.7% at 263 K. Second, to improve the performance of the cooling factor, the researchers further paired cooled LED with a photovoltaic cell that converts part of the emitted light energy into electrical energy. For applications near room temperature and moderate power density (1.0-10mW/cm2), the electroluminescent cooler can operate with a higher performance factor (predicted to be 1.7 times higher) using the material mass in the existing GaAs device.
GaAs is a III-V compound semiconductor material with a suitable energy gap to match the solar spectrum and can withstand high temperatures. Compared with silicon solar cells, GaAs solar cells have better performance.
As shown in Figure 4, Sheng and colleagues [4] prepared a miniature thin-film double junction GaAs photodiode device and investigated its photon and carrier transport behavior under different wavelengths and intensities of excitation light. The experimental tests show that the photon recycling effect is closely related to the excitation light wavelength and power, and the photocurrent and excitation light power of the double-junction cell show super linear and linear characteristics under blue-violet light (400-480 nm) and near-infrared light (~800 nm) irradiation, respectively. Meanwhile, the photon recycling effect can significantly improve the current matching between sub-cells under high-intensity excitation light irradiation to achieve a broad-band, high-efficiency photovoltaic response (wavelength 400~800 nm, external quantum efficiency close to 50%).
Figure 4: Schematic diagram of the optical process inside a GaAs double-junction photodiode under 475 nm illumination [4]
Figure 5: Schematic diagram of PV/T heterojunction: (a) Separate channel system;
(b) Dual channel system[5]
In terms of commercial applications, due to the high manufacturing cost of GaAs, terrestrial PV plants are rarely used. However, the current new growth technology has greatly shortened the time to make solar cells, which is expected to bring down the process cost significantly and make the large-scale commercial use of GaAs cells possible.
References
2. Valdivia C E, Wilkins M M, Bouzazi B, et al. Five-volt vertically-stacked, single-cell GaAs photonic power converter[C]//Physics, Simulation, and Photonic Engineering of Photovoltaic Devices IV. SPIE, 2015, 9358: 48-55. https://doi.org/10.1117/12.2079824
3. Xiao T P, Chen K, Santhanam P, et al. Electroluminescent refrigeration by ultra-efficient GaAs light-emitting diodes[J]. Journal of Applied Physics, 2018, 123(17): 173104. https://doi.org/10.1063/1.5019764
4. Ding H, Hong H, Cheng D, et al. Power-and spectral-dependent photon-recycling effects in a double-junction gallium arsenide photodiode[J]. ACS Photonics, 2019, 6(1): 59-65. https://doi.org/10.1021/acsphotonics.8b01404
5. Hassani S, Taylor R A, Mekhilef S, et al. A cascade nanofluid-based PV/T system with optimized optical and thermal properties[J]. Energy, 2016, 112: 963-975. https://doi.org/10.1016/j.energy.2016.06.142