• Kamaldeep Singh

Gallium Nitride: Is it the new Silicon?

A MOSFET (Metal-Oxide-Semiconductor Field-Effect transistor) turns ON when there is a current flow from the source to the drain. The channel creates a so-called gateway for the current. The gate voltage is used to establish a channel only after which the current flow can happen. Reducing the size of the transistor reduces the channel length over which an electron has to travel under the applied electric field which leads to Quantum Tunneling wherein the electron can cross the channel even in the absence of the field or no voltage at the gate terminal. Scientists and researchers are constantly working on new materials to complement if not replace Silicon as the building block of our current technology. One such latest find is Gallium Nitride (GaN). So what makes GaN the successor to Si? GaN is an ultra-wide band gap semiconductor with a band gap of 3.6eV, much higher than Si, which makes GaN suitable for higher voltages than Si can survive. GaN can conduct electrons 1000 times more efficiently than Si making GaN far more energy efficient than any Si predecessors. Because GaN transistors are tolerant to higher temperatures (~400 °C), they make ideal Power Amplifiers at microwave frequencies. Also, the need for large heat sinks is abridged and more compact designs can be constructed using GaN.

Figure 1: GaN FETs have less overshoot or produce a stable result quickly than Si based MOSFET GaN manufactured devices are smaller than the Si counterparts, hence more GaN devices can be placed on a given chip area with an increase in the performance parameter. GaN has low resistance resulting in low conductance losses and draws less power. Because of less switching times and switching losses GaN has a future in switching applications. Major application of GaN can be in the microwave radio-frequency applications such as microwave ovens as a microwave source.

Figure 2: eGaN FET GaN isn’t that new. It is widely used in Light-Emitting Diodes since the 90s. Violet LASER diodes make use of GaN substrate. GaN LEDs are also one of the few devices which can be used as a blue LASER device.

Market Scenario With the advent of GaN a huge opening has been created in the patent space. “The future GaN power devices market is also depending on the global patent landscape and coming mergers and acquisitions,” explained Dr. Nicolas Baron, CEO of Knowmade, a partner of Yole. Samsung holds the maximum number of patents for GaN as per reports by patentinsightpro.com. Dominant players of the current GaN market include the likes of Samsung, NXP Semiconductors, Fujitsu Ltd., Texas Instruments, GaN Systems, Inc., Efficient Power Conversion Corporation, Inc and Toshiba Corporation. Efficient Power Conversion Corporation has been developing numerous products ranging from FETs to development boards with GaN and is the leader of the market with 19.2% share in the market. Numbers of start-ups are also working on the technology and are looking for ways to implement GaN in commercial products. Power efficient behavior of the GaN finds a great use in smart vehicles for increasing the range of the vehicles of the future. Related Patents As soon as researchers found out the capabilities of gallium nitride, numerous patents were filed worldwide by various research institutes and companies concerning fabrication of GaN based semiconductors and optical devices. Some of the earliest patents include: Gallium nitride compound semiconductor light-emitting device (US 5,905,275) Toshiba and Kawasaki, Japan filed a patent explaining a method for fabricating a GaN LED using sapphire substrate as a support. Light emitting device includes formation of a buffer layer using materials having lattice constants close to GaN semiconductor compound (e.g. ZnO, GaN, AlN, GaAlN, LiAlO, LiGaO, MgAl-O, or SiC) on the sapphire substrate on which n and p layers of GaN are formed. The n- and p-type electrodes are formed such that they are on the top and bottom surfaces. Earlier LEDs using sapphire had electrodes on the same surface which posed a problem as it is difficult to form holes in the substrate leading to increased chip size. Such devices had high resistance in turn reducing light emission efficiency.

Figure 3: Describing the trench with 2 side walls This particular invention aimed at solving these problems of a decrease in the yield of devices and degradation of the device characteristics. The fabrication process involved forming a trench with 2 side wall surfaces which extends from the top to the bottom surface and inclined so as to converge downwards. Further, depositing a buffer layer onto which gallium nitride compound semiconductor is deposited using MBE or MOCVD. The substrate from the bottom is then polished until the buffer layer is exposed, a portion of which is wet etched to expose the n-type electrode. A SiO2 protective layer is formed on the stacked gallium nitride compound semiconductor and a p-type electrode is formed by creating a contact hole.

Method of fabricating a gallium nitride based semiconductor device with an aluminum and nitrogen containing intermediate layer (US 5,389,571) This patent by Pioneer Electronics describes a method for fabricating a gallium nitride type semiconductor device comprising of a Silicon substrate, an intermediate layer consisting of a compound containing at least Aluminum and Nitrogen on a part or entirety of the single crystal substrate of Si. The method also involves the formation of at least one layer of a single crystal of (Ga1-x Al) 1-yInN. More particularly, the invention is a method to form on a silicon (Si) substrate a high-quality (Ga1-x Al) 1-yInN single crystal, a material for emitting or detecting light with a wavelength of 200 to 700 nm.

Figure 4: Describing the structure of the device The invention featured the use of AIN as an intermediate layer to grow the GaN layer on a Si substrate. The use of AIN can yield a single crystal of (Ga1-x Al) 1-yInN with very high quality and considerably excellent flatness as compared with the one obtained by direct growth of GaN on a Si substrate. The invention results in high current injection, thereby resulting in a gallium nitride type semiconductor device, particularly a semiconductor laser diode. Aluminum gallium nitride laser (US 5,146,465)

The invention aims at creating a high purity single crystal gallium nitride layers over sapphire substrates, which will be used to fabricate a family of optical devices such as LASERs. It features construction of a solid state ultraviolet laser, thereby providing an efficient, compact, rugged and lightweight alternative to the existing ultraviolet laser devices.

Figure 5: Aluminum gallium nitride laser The invention uses the fact that adding materials like Zinc to GaN improves the material's electrical, optical and physical properties and points out how coating a sapphire substrate with aluminum nitride can improve growth of GaN on the substrate using better lattice match between gallium nitride and aluminum nitride. Is the industry ready for GaN? GaN tech is new and is relatively on the expensive end when compared to Si devices owing to increased manufacturing costs of GaN. We have been working with Si since the inception of semiconductors. We have devised all the manufacturing processes and logics keeping in mind the properties of Si, it is abundantly available, its processing is easy and to replace Si abruptly with GaN will affect how we deal with the electronics. Every new piece of tech needs to be studied and tested constantly for steady behavior so that it can be rolled out to customers. The manufacturing process for GaN is not perfect yet and can cause defects impairing its performance. Though, some are trying to grow GaN on Si by making use of the existing technology. One way to tackle the price problem in case of GaN is mass production but again there is no accurate method for the same as of now. Researchers are on a constant pursuit to find new materials which can cross ‘the limit’ and GaN is one of such materials. Enter Gallium Oxide, GaO has a much higher band gap than GaN and can become the needed change in power electronics by eliminating the need for bulky cooling systems and reducing power consumption. But it will take a lot of R&D needed change in power electronics by eliminating the need for bulky cooling systems and reducing power consumption. But it will take a lot of R&D before it can dominate the electronics arena. Still it’s a long way to go before we can see these new materials replace Si in its entirety. References

[1] Gallium nitride compound semiconductor light-emitting device. https://patents.google.com/patent/US5905275A/en?oq=US+5%2c905%2c275 [2] Method of fabricating a gallium nitride based semiconductor device with an aluminum and nitrogen containing intermediate layer. https://patents.google.com/patent/US5389571A/en?oq=5%2c389%2c571 [3] Aluminum gallium nitride laser. https://patents.google.com/patent/US5146465A/en?oq=5%2c146%2c465 [4] https://epc-co.com/epc [5] https://epc co.com/epc/cn/GaN%E6%8A%80%E6%9C%AF%E6%9D%82%E8%B0%88/Post/13752/Gallium-Nitride-Brings-Sound-Quality-and-Efficiency-to-Class-D-Audio (Efficient Power Conversion Corporation) [6] Gallium Oxide Could Challenge Si, GaN, and SiC in Power Applications. https://www.powerelectronics.com/alternative-energy/gallium-oxide-could-challenge-si-gan-and-sic-power-applications [7] Gallium nitride https://en.wikipedia.org/wiki/Gallium_nitride [8] What is GaN? https://epc-co.com/epc/GalliumNitride/WhatisGaN.asp

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