Gallium Arsenide (Finally) Contends With GaN and SiC in One Regard: Space Applications
GaAs has long been the bridesmaid but never the bride. However, because of its resistance to radiation, it is still the go-to choice for space-based applications.
Like gallium nitride (GaN) and silicon carbide (SiC), gallium arsenide (GaAS) is a wide-bandgap semiconductor material, (WBG) but the similarities largely end there. Unlike its siblings, GaAs is not a technology that is specifically keyed at handling large amounts of power.
The gallium arsenide compound. Brown represents gallium atoms and purple represents arsenic. Image courtesy of Shandirai Malven Tunhuma from the University of Pretoria
Long the bridesmaid but never the bride, gallium-arsenide (GaAs) is costly, toxic, and difficult to work with. However, because of its resistance to radiation, it is still the go-to choice for space-based applications.
It also offers the key advantages of low noise and low power consumption. For that reason, GaAs power amplifiers are a popular choice for cell phone OEMs to use in their transmit circuits.
GaAs for Solar Cells
GaAs is one of the most common materials used for photovoltaics. An article by Alta Devices explains the efficacy of GaAs in the fabrication of solar cells.
The most important feature is the high-efficiency GaAs solar cells offer over their silicon counterparts. Alta Devices claims the advantage is almost two to one, which means a lot less land has to be covered with solar cells to garner a given amount of electricity. The company claims the world’s efficiency record of 29.1%.
Thin, flexible, lightweight GaAs solar cell. Image used courtesy of Alta Devices
In addition, the power output of all solar cells decreases with ambient temperature. GaAs solar cells lose very little electrical output, even in high heat.
Manufacturers Honing In on GaAs Amplifiers
GaAs virtues lie in its speed, UV-resistance, and high electron mobility, making it especially useful in aerospace applications. But because of the difficulty of manufacturing GaAs amplifiers, there are relatively few manufacturers active in this field. Analog Devices is one exception.
Exploiting these key advantages, Analog Devices has recently introduced its ADH519S, a low-noise amplifier for aerospace. Because this device is so new, details are scarce; but we can definitively say that it is a GaAs-based, low-noise amplifier operating over a 17.5 GHz to 31.5 GHz bandwidth.
When operating over 17.5 GHz to 28 GHz, the ADH519S has a noise figure of 4.0 dB and a gain of 11.4 dB. Over the 28 GHz to 31.5 GHz range, the corresponding figures are 6.9 dB and 9.5 dB.
Analog Devices is one of the few players that has been in the GaAs business for a long time.
For example, its HMC7950 operates from 2 GHz to 28 GHz. From 2 GHz to 5 GHz, the typical gain and noise figures are 15.5 dB and 3.0 dB, respectively. From 5 GHz to 18 GHz, the figures are 15 dB and 2.0 dB, and from 18 GHz to 28 GHz, the figures are 16.5 dB and 2.8 dB.
Typical application circuit using HMC7950. Image used courtesy of Analog Devices
ADI also has produced the HMC392A, which operates a 3.5 GHz to 7.0 GHz range, features a gain of 17.2 dB with a noise figure of 1.7 dB.
The device uses a 5 V power supply and comes in a 1.3 mm x 1.0 mm x 0.1 mm package.
Devices of this type can be characterized as an MMIC, or a monolithic microwave integrated circuit. More specifically, it is a pHEMT or pseudomorphic high electron mobility transistor, a device described in more detail in NXP's whitepaper on practical considerations for low noise amplifier design. In a nutshell, what that means is that the PN junction consists not only of GaAs but also of other materials such as AlGaAs. It is this structure that contributes to the low noise characteristic of GaAs devices.
WIN Semiconductor, Qorvo, and Macom
Representation of GaAs amplifiers beyond Analog Devices is surprisingly sparse. A few companies that are delving into the WBG material is WIN Semiconductor, Qorvo, and Macom.
WIN Semiconductor is a large, Taiwanese semiconductor foundry that specializes in producing GaAs wafers for OEMs. It offers its PIH1-10 platform for 5G front ends operating way up in the 24 GHz to 45 GHz bands. Its ƒt, the frequency at which gain is zero, is fully 100 GHz. Tx power can be as high as 30 dBm, and most importantly, the Rx noise figure is only 2.5 dB at millimeter-wave frequencies.
Qorvo is also a producer of GaAs devices, and it offers foundry services. Qorvo features an entire page of discrete transistor components that use the company's "ultra-low-noise 0.15 µm pHEMT and 0.25 µm E-pHEMT processes," which in turn gives developers more control when designing low-noise amplifier circuits.
Macom, too, is active in this field. Macom claims to be the "first pseudomorphic High Electron Mobility Transistors (pHEMT) supporting high volume components required for commercial applications." The company asserts that its advances in GaAs have allowed them to produce:
- Discrete devices
- Control components
- Mixed-signal processing and converters
- Driver amplifiers
- CATV amplifiers
- Low-noise amplifiers (LNAs)
- Power amplifiers as single-purpose and multi-function MMICs
What's Next for GaAs?
What does the future have in store for GaAs? One company, Lumentum, has indicated some promise in employing GaAs in other ways; they have implemented GaAs in its new portfolio of datacom laser chips for data centers and 5G wireless applications.
While it's evident that GaAs is especially useful in aerospace applications and solar cells, the question lingers whether GaAs will find its niche long term.
Are you one of the rare few that has hands-on experience with GaAs components? Share your experiences in the comments below.